Should I change to a Tankless Water Heater?

[Danny Jones]

My hot water heater needs to be replaced, and I keep hearing about tankless water heaters, is there anyone here who owns one who could provide me with First hand information, are they a better alternative to tank water heaters?

Thanks in advance for any advice. :)

[Rob Beckers]

Hi Danny,

I'm contemplating the same question. Since my (natural gas tank-type) water heater is a rental, and just paying the rent pays for a new one every two or three years (came with the house we bought). So, I'm looking forward to replies to your question as well.

A little search (http://www.greenpowertalk.org/showthread.php?t=1959&highlight=tankless) shows there are members with experience. Hopefully someone will chime in. There have also been several articles about tankless water heaters in Home Power Magazine. In case you have access to those.

I grew up in The Netherlands, and there always lived with a tankless water heater (most of the years that I lived by myself over there I had a combination tankless water heater plus house heating in one box). My experience has been good with them, they just work, never run out of hot water, with the occasional cleaning needed of the heat-exchanger if you live in a hard-water area (my parents do). Most of Europe seems to use tankless heaters. Other than that you avoid the stand-by losses of a tank-type heater, which can account for 20 - 30% of their energy use if I remember right (depending on your hot water habits). They also last far longer than the average tank-type heater. If you have any plans for solar hot water look for a type that has a variable output heater, so it can handle pre-heated water and add just enough to reach the set temperature.

The part I don't know about is current types, prices, quality, and their pros and cons. Hopefully others will fill this in.

-Rob-

[Paul Bailey]

I dug up this old tankless article of interest.:)

[Ralph Day]

Hey Paul,

Tanks for the article. It is informative and useful, and i've had a tankless for almost 4 years.

ralph

[Wilco Vercoelen]

I would go for the Rinnai 2532 or so. The are a little bit more expensive, but as far as we know it is good quality. I would recommend combine them with a solar hot water system. Make sure it is a modulating tankless unit so it can adjust to the water temperature that is going into the unit. It uses less energy that way and also the flow is larger than if it was colder water going in.
Hope this help.

[Danny Jones]

Thank you everyone for all the great information so far, I'm at the point now where I think we would like to go tankless, does anyone here have a brand name preference?

[Rob Beckers]

The local Costco here is now offering the sale and installation of the Rinnai R85 Plus as a service (they contract with local installers). I'm sorely temped, as I'm still paying every month for a rental tank-type water heater. A little search for this brand/model shows good reviews, efficient, and it's a modulating heater so it can be combined with solar at a later date.

Of course, it all depends on the price they're asking for the unit plus installation. Costco tends to have good prices though! I going to give them a call after the holidays.

-RoB-

[Stewart Corman]

I'll put on my chemical engineer hat today.
I've been reading the posts and recommendations and the link provided.

Off the cuff, I'd say that on demand domestic hot water is the last option I would choose. I am presuming that storage space is NOT a consideration.

Insulation on new 82gal tank heaters are fine ..don't lose 30% ... that is total BS ...and bigger is better (less surface area/volume)

There are two types being discussed ..electric and gas ..ignor oil

gas:
tank units for 50gal <$400
That Rinnai 2532 gas unit costs about $1299 ...HD has other brands for about $1000.
All gas fired units have some losses , usually around 10+%.
The worst thing for a gas fired unit is to turn on and off frequently ...
the faster the heating time, the poorer the efficiency
can't preheat tankless from RE

electric:
82 gal tank heaters <$500
All electric heating is 100% efficient.
The electric ones use 4 x 7KW elements ...that's a lot of wiring cost.
Don't have the capability of using cheaper night rate electric which is 30% right there
Water heat storage for RE is far better than batteries/inverters which have over 30% losses and high investment cost in electronic modules
I estimate my electric domestic water heating bill at $12/mo ...hard to justify an ROI for expensive units ...units last 12+ years, replacement elements cost <$15

BTW, a Watts tempering valve is used to keep tank at 190 degrees heated at night and mixes cold water to deliver 120 (?) degrees to house. Day/night timer costs about $20.

I must be missing something basic here, because I just don't see it!!

Stew Corman from sunny Endicott

[Paul Bailey]

Hi Stew : I'll give you a more detailed reply here when I get more time, and propose a couple scenarios' as to this replacement. Most people that have a tankless seem to really like them and there Capability and or benefits aside from the high purchase price. Oh heres a couple pics of a commercial Kitchen install Vs the 60 gallon that was removed. Oh as well I think there are several members here that are preheating the feed to the tankless with Re ( solar preheat) but they'll have to chip in as we go .... Merry Christmas and Happy New Year to all of you and your families.. It's been a good year of conversation, Paul :)

[Joe Blake]

One of the things not always taken into account, but is VERY important in Australia, is the amount of water consumed. Up until about 18 months ago I was the victim of an electric tankless water system. Admittedly it was a very basic system, without much in the way of sophisticated temperature controls, but I found it dangerous and wasteful of water because as a good water conserving citizen I have a "trickle" shower rather than a "blast" shower, but this stupid piece of electrical dumbery would only activate above a certain water flow, so I'd try and have a trickle shower and find only cold water or I'd increase the flow until I heard the click as the solenoid closed then I'd be parboiled by excessively hot water which I had to cool down by adding more cold water.

Thankfully the heater reached a well deserved demise and the owner of the house fitted a tanked solar hot water system with an electric booster. Ah Bliss! Trickle shower at exactly the right temperature with the minimum water consumption.

So whilst not everybody has the same paranoia about conserving water as the average Australian (especially West Australian) water wastage is still something I would suggest be at least a small factor in considering whether to go to a tankless system.

Joe

[Rob Beckers]

As Joe rightfully notes, I agree that tankless is not for everyone. I've lived with them in Europe for about half my life (before moving to other continents) and never had a complaint about them. It all depends on what you need them for.

Stew, why do you say you can't pre-heat tankless with solar? That's exactly what I have in mind for the future. A modulating tankless water heater (that can modulate the BTU output of its burner) will take input water of any temperature and bring it up to the set output temperature. As a consequence, if the input water is already at the set temperature (from solar pre-heating) the burner of the tankless heater will not come on at all. The current crop of tankless also modulates water flow, so if its burners at full blast can't reach the set output temperature it'll drop water flow. I should mention that not all tankless heaters are suited for solar pre-heating, you pay for the modulating feature.

As for savings from eliminating standby losses, I have no numbers. I have a feeling that Stew is right, in that the tankless manufacturers exaggerate standby losses. What the actual numbers are and how this translates to money I don't know. If anyone has a link to a serious study about this I'm all ears. Bigger is not better though in tank-type, since the absolute heat loss is larger for larger tanks, and that's what you pay for in real dollars.

Cycling burners (and resulting inefficiencies) is more of an issue in tank-type heaters. In them the burner needs to come on regularly to keep the tank at the set temperature (again related to standby losses). Tankless heaters only come on when needed, and their burner then opens up as needed (for a modulating heater). Efficiencies for the models I'm comparing (my current tank-type and the Rinnai R85 tankless) are both in the low 80% range. Mid-efficiency models.

For me it comes down to either buying a tank-type heater to replace the one I'm currently renting, and looking at replacing that once over a 20-year span (even with replacing anodes I've not heard of a tank-type surviving more than 10 years, and I've asked people around here who do replace their anodes). Alternatively I can buy a tankless, with a life expectancy of 20 years. In terms of money, cost of operating plus acquisition, it's likely a wash between the two, when viewed over 20 years.

-RoB-

[Ralph Day]

Happy Holidays everyone

Stew, did you miss the solar pre-heat to tankless water heaters at Les and Gwen's and my place on the tour? I even had a propane-less shower after only 1 full day of sun on the collector...in the first week of December! The fall and spring use the solar preheats the Takagi water just fine, it modulates itself to the temp of the incoming water just fine.

ralph

[Stewart Corman]

Ralph, you made a few goodpoints and I wasn't thinking offgrid to start with in this conversation. OK, let me clarify a few points which may have gone astray.

Firstly, in Paul's response to me with the pics, the point being made was to remove a large bulky tank with a streamline (reads "neat") installation. My comment about preheat was that if you throw out the large tank, you don't have a means to store large BTU volumes ...obviously, if you and Les are using solar panels and have storage capability built in, then a tankless unit for "backup" is the way to go ...then again why spend $1200 for a unit which might only go on ten times a year? I'd buy the smallest gas tank heater for $275 at Sears and use it "on demand" with a manual switch.

Now to take issue with a few comments by Rob:

I got rid of my old 82gal tank heater after 20 years because I got tired of looking at it ..changed the element once , second time it was filling up with 3 inches lime from hard water...didn't even know they had an anode until about two weeks ago. That aerobic filter we had talked about earlier eliminated the lime.

My neighbor never changed his heating element ...he built his house in 1958 ...same tank heater!

Bigger is better ..less surface area/volume ..more efficient heating for gas ( electric irrelevant at 100%)

Efficiency is a bogus argument if my total electric consumption is $144/yr and gas would cost 1/2 that amount, even at today's prices. And where do those inefficient BTUs end up anyway ...warming up the house! Just like the argument a buddy mentioned that I should replace my perfectly good 15 year old frig with a new "high efficiency" model to "save money"...total BS!!

Modulating the pressure? sure invalidates the KISS principle to me ...no wonder they cost $1200!!

BTW, with scrap pipe and fittings around here, a 5KW/220v element, some insulation, and a temp sensor off an old tank heater, I could build a tankless "on demand" for about $50 ( and probably have $30 left over).

Me energy efficient ??? not by a long shot

I will agree that long supply lines are not advantageous ...I used 3/4 copper to feed my bathroom on the other side of the house, so as not to have large pressure drops ...it takes 2 minutes to heat the pipes and water to get that shower hot ..and admittedly they cool off when water is turned off ...

then again, turning on the steam room in that shower for 15 minutes using 5.5KW element isn't exactly energy saving ...did I mention that the 55inch Plasma at 500watts can warm a small room by itself, especially when the 1000 watt surround and 250 watt subwoofer complete the home theatre experience....BUT, my electric bill is under $100/mo (<30KW/day)..... I'd need a hell of a lot of battery banks in off-grid to keep this stuff float'n

But I thought the premise of this thread was tank or tankless and no mention was made of offgrid or as solar backup ..I gave my $.02 comparing the two and tankless comes up short as a standard installation in an ordinary residence ...my cousin drives to the supermarket in her new Escalade, but her old Saturn is more streetwise. Are we talking want or need?

Stew

[Paul Bailey]

BTW, with scrap pipe and fittings around here, a 5KW/220v element, some insulation, and a temp sensor off an old tank heater, I could build a tankless "on demand" for about $50 ( and probably have $30 left over).

Me energy efficient ??? not by a long shot



Hi Stew : Tankless Electric water heaters are sometimes up to 40 or more Kw for capability of heating flowing water for a household., these sequence start similarly to a Gas Tankless unit to maintain output at various flows to maintain temp to within a couple degrees...
Energy Efficency Has been a quest / journey/ an experiment for me to keep my Electrical bills in line for my household over the past 20 years.,I've Had 60 compact flouresant bulbs for close to 20 years, I used to pay 6 cents a Kw now its 15 cents, I've Chased wasted Killowatts way before ( the Green home existed , the Leed homebuilding program, the Government Nrcan, and everykilowatt counts program). I clearly understand the value of an energy dollar and what and where its being wasted, (electrical as well as BTU heating energy) I have worked these numbers back and forth to the detail.. Oh did I mention I'm in an all electric house appliance house...No gas Yet. Since I'm a heavy user I get the quickest payback on justification of any efficiency upgrade where as you may not. Happiness is a 30 to 50 dollar electric bill when my next door neighbor is $175 a month, with a Much small house and less than 1/2 the people . We are all in the same boat here as Gas/fuel /and other energy prices rise ,..Hopefully not as high as Europe ..but thats another story Paul:)

[Stewart Corman]

Paul,
I was remiss in stating that I have a situation here that I cannot fully understand.
We had a utility increase this year that was approx 20%. But my last three bills have been around $85, whereby in previous years bills of $120 were not uncommon and peaked at $135/mo mid winter.

There are a few differences:
1) burning firewood exclusively so far, so no fuel oil injector pump, but hot water circulator runs continuously (20 watts?) and forced hot air fan blower is on 12+ hrs /day (5.2amp rating on motor?)

2) both kids out of house!
above means two less puters on 24/7, TV not used as a night light


BTW, I saw your post on the new frig, and I was surprised at the savings ...but how old was the old fridge?...I would need a "Kill-a-watt" to see how much my frig actually uses and then have to figure out how to compare to new label specs. The old line "figures don't lie, liar's figure"

My chest freezer in cool basement is probably 40+ years old ( was top of the line Sears back then!) ...BTW, I tried the experiment with insulation and then measuring external temp between insulation and freezer and couldn't determine there was any benefit.

Side comment: next door retired neighbor with slightly larger house is all electric and makes no effort to conserve ..inground pool, central air. the works ..a few years ago they claimed that they ran up an $8K electric bill for the year ..want to add the 20% increase ???? And who would they sell the house to eventually with a $800/mo bill?


Stew

[Paul Bailey]

Hi Stew : all my numbers were verified with a Kill A Watt meter for at least 3 months as part of my verification. Oh the fridge was 16 years old. My parents Have 2 25 plus year old fridges and there begining to see some light as there bills are going berzerk but are lacking the knowledge to see just why. I'll give the manufactures alot of credit here as its been a long road here and in order to STAY in business You need to be efficient along with your products or you are not going to last.:)

[Mike Arant]

I am building an earth sheltered concrete home (marant1946.blogspot.com) and have decided to install two separate water heaters. One will be a Takagi T-K3-OS, which is a new model that mounts on an outside wall and runs on either LP or Propane. It has anti freeze protection and the advantage of no fumes or danger to inside spaces. After looking at all the available heaters I think this is the best at this time. With free shipping and 10% off at Homeclick it comes in at close to $700 which I figure is about a 6 year payback with a lifespan of at least 20 years. I have reviewed the installation instructions and believe will not be too bad to install.

The other water heater will be a conventional electrical in the mechanical room. It will primarily serve the guest bathroom and will be turned off when we do not have guests, which will be most of the time.

I also intend to interconnect the systems with a cut-out valve just for redundancy in case we run out of propane or lose power.

[Paul Bailey]

Or You could choose a new stand alone heat pump ( air to air) water heater

[Ralph Day]

Mike
I have a TK-Jr operating in my basement (no problems) on a short out the wall stack (1.5' total). I installed the temperature sensor before going off grid, and the consumption when the temp outside went below freezing was over 2Kw per day. that's only 25 cents if you're buying it but sometimes a significant portion of a day's RE inputs (yesterday .5kw sun, .1kw wind).

Something to think about depending on your geographic location. Takagi's are limited on the block heaters too. They only keep the exchanger and the intake points heated, not the inlet water or outlet water lines. Freeze damage is not warranty covered (installation manual).

I overcame the freeze problem by forcing house air through the unit with a 12watt muffin fan and an old furnace duct boot. This drives house air through the unit (around the heat exchanger) and out the Z-vent. I suppose i could put the vent on a thermostat switch, but i only run it when the outside temp gets below -5 c (ie just haven't got around to it). The workaround also helps with the number of air exchanges the house needs...i heat a little more air, but the winter air quality is better, not so stuffy.

Ralph

[Rob Beckers]

Stew, as for the difference between an old vs. new fridge: I can confirm going from an 18-year old fridge that used 1680 kWh/yr to a brand new LG fridge that uses just around 500 kWh/yr. Both are 25 cu. ft. models. That is an annual savings of 1180 kWh, or at current prices $168/yr. Energy consumption was measured with a Kill-a-Watt meter.

-RoB-

P.S. Costco's tankless installer has contacted me yesterday. He's coming for a visit in the next few days to see what's needed and how much it will cost to get a tankless water heater installed.

[Ralph Day]

Rob,

Don't forget the advantages of RE. Solar Domestic Hot Water has the fastest payback of any RE investment. I'm really happy with my Enerworks system (recently won awards from some building society).

Today i realized after running the genset for several hours, that there's many Kw's of power i'm wasting with space heaters that i may be able to use to heat water. Remember my system has a 60 gallon electric tank as the holding tank for the SDHW, with elements and controls for 240vac...exactly what comes in the house from the genset. After 2 hours of running there's plenty of genset capacity to run the water heater. Imagine, solar hot water, propane flash heater and now diesel hot water!:D Tech question submitted to Enerworks, wating for reply.

Happy new year all

ralph

[Paul Bailey]

Any and all forms of energy storage in the form of mass(BTU's per Lb. or Kg) is always compared to water. This works for heat as well as cooling, I was intrigued by this as a child when I walked into an Ice house in the middle of a 90 deg (32 deg.C) day in July and it was real cold in there, Your can store Both forms a long time with the proper insulation... Oh for those not from this neck of the woods in more temperate climates , This is ice blocks being cut from a lake for refrigeration purposes prior to the 1950's...

[Rob Beckers]

Diesel hot water... Now there's a concept Ralph! ;)
Are you talking about the genset coolant? Running this through a heat-exchanger in your solar hot water tank.

The tankless sales rep visited this afternoon and gave me a price: $1950 plus tax to install a Rinnai RSi75 (he must have gotten the type number wrong, there's no such thing as far as I can tell). That is disappointingly expensive! What's more, when I asked if there was any discount in this for going through Costco the reply was "no". It would not have made any difference if I had contacted his company directly. Seems there's no buying-in-bulk power of Costco behind this, as in getting the hardware cheaper.

As to the needed hardware, a Rinnai R85i can be had for $795. A vent kit with the needed pipe lengths for my case for about $200. A valve kit, to make flushing the unit easier, for $85. That makes for a total of $1,080 plus tax. In addition to this, there will be a little copper water pipe and assorted fittings (the new unit would sit about 3 feet from the current hot water tank, and about 15 feet of 3/4" black iron gas line needs to be run.

My current thinking now leans to do my own install. The only thing I will not touch is the gas hookup, so there will be some expense for that (say around $200). All the other aspects involved are familiar territory. If anyone has experience in installing a Rinnai please let me know. In particular I would like to ask a few questions about the vent kit.

-RoB-

[Paul Bailey]

Hi Stew I did find this on hot water costs a few years ago and Joe will like it since its from down under.:)

[Ralph Day]

No Rob

Not the coolant from the genset but the actual power generated, but not used. During absorb phase of charge there is eventually enough electrical capacity to run the water heater as well as house loads and charging.

To avoid deficit cycling of the batteries i've found it's necessary to do 2-3 hours of absorbing charge when the charge demand might only be less than a kilowatt from the 10 Kw genset...hence the power dump. I don't get enough solar/wind to warrant power dumping to heat water throughout the year. Then there's the SDHW Enerworks system which gets hot water from the sun for 8 months of the year (almost).

ralph

[Rob Beckers]

I've been doing a little more digging into stand-by losses of tank-type water heaters. As it turns out, for gas fired tank-type heaters, which is what I currently have, most of the standby losses occur through the chimney located in the middle of the unit. Additional insulation would make absolutely no difference. It's simply using the heat-exchanger in reverse and siphoning off heat from the water in the tank, to the exhaust stack (creating a chimney effect, drawing air through by itself). This lost heat doesn't even go towards heating the house where it would be useful in winter (ie. staying indoors), it goes up the flue. An electric water tank does not have this problem and is indeed much more efficient. Then again, heating water with electricity is an expensive proposition here (about 2x the price of using gas to heat water).

Standby losses are published in the form of the unit's "energy factor" (EF). While the Rheem tank that I have lists an efficiency of 82% (the fraction of energy available in natural gas that gets turned into hot water), it has an energy factor of 0.64, or 64%. My understanding is that the EF is measured by heating once and letting the tank stand over a 24 hour period. That means my gas fired water heater looses about 18% of its heat every 24 hours. By the way, the tank-type heater I have is a fairly high-end Rheem.

EFs for electrical tank-type heaters are typically around 0.80 - 0.85. For on-demand tankless gas water heaters it's around 0.80 - 0.84.

Now, how to put a money figure on the standby losses of a tank-type gas water heater?

Heating up my 50 gallon tank from 45F to 115F takes: 400lbs * (115-45) = 28,000 BTU.

Assuming 10% (out of that 18%) goes up the flue every 24 hours (conservative estimate), that makes for a loss of 2,800 BTU/day.

For a year that is 365.25 * 2,800 = 1,022,700 BTU/year.

At an average of around 1050 BTU/ft^3 that makes for 974 cubic feet of natural gas, or 27.6 cubic meter per year.

The current differential rate for a cubic meter of gas in my neck of the woods is $0.428. That makes for a cost of around $12 per year due to standby losses. Assuming gas prices stay where they are (yeah, right!), that makes for $240 over the 20-year life of a tankless water heater.

Comments welcome!

-RoB-

[Paul Bailey]

Ok Rob ..Good analysis. On the Rheem tank Forget the Efficiency for now. The Energy factor is your real world Number for comparison. The standby loss is factored into this as stated. So the big picture states that you are only utilizing 64% of every dollar ( Or 64% of every cubic/Meter of gas) that you are using in this appliance. This Kinda washes out most of your Math and back to the drawing board but a nice refresher to challenge me on something that I Used to Know .( don't get to washed up in the Math) Anyway the Tankless dominates by far since it starts at 85% burn with no EF losses so ends up at 85% EF. What is striking about this is your not alone here with an appliance that appears to be OK but is wasteing 35% up the stack and millions like you and I and most of North Americans need some re-education an whats real Vs perceived with Energy and Efficiency. Comments Welcome again ..I hope this helps. Paul:)

[Rob Beckers]

I've received some off-line feedback on my calculations indicating the intent of what I was trying to calculate wasn't very clear. It was an attempt to quantify the amount of energy going up the flue due to standby losses of a tank-type heater, and it assumed the rest of the standby losses would go towards heating the house (in my house the water heater is in the basement, within the thermal envelope of the house).

I've also found that the definition of energy factor I used was not entirely correct. With that in mind here is a second attempt at quantifying standby losses. This time I'll try to calculate a number that represent all of the standby losses in a typical tank-type gas heater (using the Rheem I have as an example), even if some of the lost heat goes towards heating the house it still needs to be replaced to reheat the water in the tank. I've also found the formal definition of the energy factor for water heaters (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=e52d7132accea00e5f38bf1cc8705803&rgn=div9&view=text&node=10:3.0.1.4.16.2.9.9.5&idno=10), not an easy one to find.

The test procedure for finding the energy factor goes roughly as follows: A water heater is allowed to heat up its contents to 135F (for a tank-type). Then six hot water draws are made over a 24-hour period, totalling 64.3 gallons. After each draw the water heater is allowed to recover. At the end of the 24-hour test the total energy consumption is measured and compared to the amount of energy that was taken out in the form of hot water. The input (cold) water has a temperature of 58F. Natural gas is assumed to have an energy content of 1,025 BTU/cu. ft.

To tease out standby losses from the energy factor vs. efficiency for my hot water tank I simplify a few things, hopefully the result is still in the ballpark. I'm sure y'all will help me point out the deficiencies of my calculations! ;)

Over a 24-hour period the water heater has to heat up 64.3 gallons of cold water from 58F to 135F, a differential of 77F. Doing so takes: (64.3 * 8.33)lbs * 77F = 41,243 BTU

The EF for this tank is 0.64, so this takes: 41,243 / 0.64 =64,442 BTU in burned natural gas to do.

Without standby losses this water tank is 82% efficient. Heating the same amount of water would therefore take: 41,243 / 0.82 = 50,296 BTU in natural gas.

The difference is what's lost in standby losses: 64,442 - 50,296 = 14,146 BTU per 24-hours.

Per year this is: 365.25 * 14,146 = 5,166,827 BTU

That takes: 5,166,827 / 1,025 = 5,041 cu. ft. or 142.7 cu. meter of natural gas per year.

At my current cost of $0.428 per cubic meter, this works out to $61 per year, or $1,220 over the 20-year life span of a tankless heater. As before, the numbers are for my current 50-gallon Rheem natural gas water heater, for other water heaters it'll be somewhat different. Also keep in mind that if gas prices go up, so will these cost numbers.

As before, comments welcome!

-RoB-

P.S. Paul, there's an easy way to spell-check messages: If you're using Firefox you can simply right-click on the edit window and select "spell check this field". If that doesn't work in your Web browser, you can use the forum's spell checker by selecting the little "abc" icon at the upper right corner of the edit window.

[Stewart Corman]

Rob,
you are trying too hard!
I'll make it easier for you"
http://www.rheemtankless.com/content/documents/Fuel%20Cost%20Calculator.htm

(will only run on IE)

report back what you conclude on orig example
looking more carefully, it may not cover the ground you were attempting?

BTW ...anyone know how you create a spreadsheet which is accessible as an htm like above link??

Stew

[Rob Beckers]

Thanks Stew, interesting and useful link!
The online calculator is a bit different animal. It doesn't isolate standby losses, which is what I was trying to do. It is useful for verification though, if I set the water volume the same as in my calculations and change EFs, I get the same BTU results. When I set the cost of natural gas, I also see the same $61/yr difference. Directly comparing the results for the tankless and tank-type in the online calculator is hard, because one is for natural gas, the other for propane. You'd have to recalc prices based on energy content to compare the two.

In any event, when set properly the online calculator verifies my calculations. So I seem to be on the right track.

-RoB-

[Stewart Corman]

Just caught an anomaly on that calculator.

An electric tank unit is listed as EF= .94
We know that electricity is 100% heating efficient, so the only loss has to be standing losses ( which go into the house anyway).
and they didn't specify 40 or 82gal tank size??
BUT ..this amounts to ONLY total 6% loss

I can't believe that a tank gas unit can be 20% loss ( 0.82 vs 0.62)..
doesn't make sense, they way the newer units are packed with 2"/R16 foam insulation

just found this comment on tankless which supports my position:
http://www.consumersearch.com/www/house_and_home/water-heaters/review.html

Downsides include the high cost -- twice or more of what you'd pay for a traditional tank-style water heater. Editors at Consumer Reports say you're unlikely to make up the extra expense in energy savings. Installation can be tricky, and gas units may require wider-than-usual vents and larger gas pipes running to the meter, adding another $500 to $1,000 to the initial installation cost. Pipe and vent issues also make installing a tankless water heater in an older home more difficult, and hot water may take longer to reach remote rooms.BTW, AO Smith makes the Sears and 12yr/40gal is the sweet spot <$400
power vent costs $250 premium and I don't know why you'd need it for conventional installation ..I had never even heard of it before this conversation

Stew

[Rob Beckers]

Just caught an anomaly on that calculator.

An electric tank unit is listed as EF= .94
We know that electricity is 100% heating efficient, so the only loss has to be standing losses ( which go into the house anyway).

Even with that heat going into the house, it's only useful in winter, and you still need to make up for it by heating more water. Extra tank insulation will not make much difference for this heat loss.

and they didn't specify 40 or 82gal tank size??

You can specify the tank size by changing the number on the left side of the calculator (gray field).

BUT ..this amounts to ONLY total 6% loss

I can't believe that a tank gas unit can be 20% loss ( 0.82 vs 0.62)..
doesn't make sense, they way the newer units are packed with 2"/R16 foam insulation

As mentioned, for gas-fired units most of the standby losses is heat going up the (central) flue. That's gone to outside, doesn't help heat the house either.

just found this comment on tankless which supports my position:
http://www.consumersearch.com/www/house_and_home/water-heaters/review.html
BTW, AO Smith makes the Sears and 12yr/40gal is the sweet spot <$400

Agreed. The install or retrofit costs make it a dubious ROI. As mentioned before, the installer essentially wanted a $900+ installation fee (more if you consider they buy wholesale and get the tankless units for less than what I can buy them for).

power vent costs $250 premium and I don't know why you'd need it for conventional installation ..I had never even heard of it before this conversation

Stew

Don't know why either, for some reason all the water heaters I see around here (at friends places) are power vented. The 50-gallon Rheem tank I have in my basement lists for around $800, probably more in Canada as that's a US Internet price.

-RoB-

[Paul Bailey]

Hi Rob And Stew; Good job on the numbers this round. I didn't check them but the $ 60 is real close . Now the 20 year number really jumps out and can direct you in the right path for a tankless decision. ( we may need another forum to discuss Efficient Heating or whatever). For those that are curious as to what I do I will repost shortly with a new topic on this,For my hot water. . Now back to this again I think most consumers are misled or simply not told at all what the real cost of ownership , then the yearly operating costs for X number of years is. More to follow , are you suprised as to the numbers Now?????:)

[Paul Bailey]

Robs Tankless Vs Gas water comparison really brings to light why the Government has implemented the Energuide Program for appliance Eff./ operating Cost Ratings. This is so important for the consumer/end user of whatever for an reasonably honest comparison.

[Ralph Day]

Rob

I think the power venting is used to preclude any backdrafting of products of combustion. When my TkJr is firing for high flow and cold input temp, it will fire with probably 140,000btu's. The average gas fireplace is 30,000 btu's. In order to get the fumes up and out the flue you need to help them along, especially if you're using house air (ie not direct vented as some are). The TKjr's spec sheet gives a max btu's of 180,ooobtu's maximum...that's about 7 litres of propane per hour at max.

To add something completely different, some folks i know locally installed a tankless ventless water heater! it's loaded with sensors (CO i presume) and such, but i even run my kitchen range hood when the oven is on i'm so paranoid about CO in the house (plus it keeps the smoke detector from screaming, usually).

ralph

[Paul Bailey]

The swinging door syndrome keeps my house vented (Kids). All Joking aside Indoor air quality is in Question these days with tighter building envelopes/constuction methods. As Ralph states a good CO detector is a must in gas/propane applications.,If not already manditory by some insurance companies:)

[Rob Beckers]

Yeah, I saw the vent-less models (to my surprise). I suppose in theory a natural gas fired unit produces mostly water vapor with just a tiny bit of NO2 thrown in for good measure. With the fairly large BTU ratings and air-tight homes of these days I'm not sure I would want all that water vapor inside my house. Then again, with my leaky house it would probably help humidify the air a bit in winter! ;)

Seriously though, I don't think it's a good idea to go vent-less. In fact I rather like the idea of drawing both the combustion air from outside and venting gases outside. For units that get their combustion air from inside it means they draw in the same amount of air from the outside through cracks and leaks to make up for the exhaust. That makeup air needs to be heated up again by your home's furnace.

As to CO detectors: I have a combination unit smoke-CO detector in my basement and another one on the main floor. Those combination units make it easy to be safe.

-RoB-

[Ralph Day]

Rob,
I found with the small Z-vent stack on my TKjr, i needed to force warm air through the unit/around and through the exchanger, to keep the temp from freezing the unit (cold air would flow down the vent plus conduction from the outside termination...nice aluminum heat sink). If you're using outside air for combustion source, then the cold outside air will be exposed to the exchanger in the combustion unit (big copper chimney is what the exchanger looks like). You'll likely have to have the block heaters activated all the time below freezing temps outside. 2kw per day for mine (I don't use them, the air keeps everything ok).

The longer the z-vent stack is, the less likely the chance of freezing, but probably the less efficient the venting...6 of one 1/2 dozen of another.

ralph

[Paul Bailey]

The longer the z-vent stack is, the less likely the chance of freezing, but probably the less efficient the venting.

I think your right Ralph: even an extra few feet of venting in room temp is ( or maybe ) just enought heat to stop this reverse flow in below freezing temps, As some of those in this group are doing.. Higher vent /tankless installed location can stop this as well since the air naturally wants to backdraft everywhere below Neutral balance. With concentric vent (see photo) the vent and unit are considered Sealed and this "river of airflow" would be greatly reduced and may be a non-issue at all.,I'm not the engineer but this is my veiw. This is a pic of 3 inch I.D. and 5 inch outside diameter concentric Pipe 1 Meter long so you's can see what this vent is.. Paul :)

[Ralph Day]

Paul
The pics on your Dec 24 post look like an inlet and an outlet stack. I've got a propane stove with pipe within pipe, but i;ve not seen tankless water heater venting like that, hence my concern about cold air (really cold air) in and around the exchanger. The Takagi install manual states quite emphatically that freezing of the heat exchanger is NOT a warranty issue, your mistake? your fix!

I ran my genset again today and all i could think about was how to get that 4.5kw from my genset to my 60gallon holding tank! For at least 2 hours of the charge run i could have been heating water. The Enerworks control unit is wired to the high limit on the tank, just wondering if 240vac applied to the tank terminals will affect the Enerworks controls. Any ideas?

rlap;h

[Rob Beckers]

Hi Ralph,

The Rinnai tankless units use coaxial vents (pipe within a pipe). They don't use Z-vent.

-RoB-

[Paul Bailey]

A peak inside an instant//Tankless water heater for those that are wondering.:)

[Mark Parsons]

Gentlemen,

My $0.02 worth of tankless experience to date.

I installed one of these Excel America Ventless LPG 1.6GPM units at my cottage this summer. Unit cost $300. So far it has done a good job.
http://cgi.ebay.ca/1-6-gpm-LPG-VENT-FREE-tankless-gas-water-heater-10002P1_W0QQitemZ290193022399QQihZ019QQcategoryZ11 5967QQcmdZViewItem

Yes, it adds some humidity to the air. No problem this time of year. Also adds some BTU's to the air. Again, no problem this time of year. At 38,000 BTUH, it is less than having all 4 stovetop burners on while cooking.

I will be feeding it with solar warmed water later this year. Unfortunately, it doesn't automatically modulate. I will be installing an anti-scald valve downstream that mixes cold water with the overheated hot. Will advise any difficulties with my set-up.

Regards,
Mark

[Steve White]

Gentlemen,

My $0.02 worth of tankless experience to date.

I installed one of these Excel America Ventless LPG 1.6GPM units at my cottage this summer. Unit cost $300. So far it has done a good job.
http://cgi.ebay.ca/1-6-gpm-LPG-VENT-FREE-tankless-gas-water-heater-10002P1_W0QQitemZ290193022399QQihZ019QQcategoryZ11 5967QQcmdZViewItem
As I was reading this thread I was wondering if anyone had noticed the flood of cheap tankless units recently. There are 5 or 6 brands that between them have a couple of dozen models, mostly gas but some electric, that are under $500...well under in some cases.

There is no question that I will be going solar preheater tankless in the new house. I have seriously considered retrofitting this house as the water wasted while I wait for hot water to make it from the utility room to my main bathroom is a constant irritant.

[Brian Knight]

My first post and I am already jumping in hot water..Ha!

This is such a great debate for Green Power because there are so many products, opinions, and strategies available for the second biggest energy user in most homes.

Great posts above. Some new details I learned form Mike's .doc. I will restate what has been implied already: Every situation is different and a compelling case can be made for virtually any product and configuration.

Generally, with existing homes its best not to change existing infrastructure and simply upgrading in efficiency when its time for replacement makes the most sense.

Iam surprised no one here has blasted tankless electric yet, allow me.. Tankless Electric is a bad choice for all but the smallest of demands. NOT green. Not cost effective. Gas/Propane tankless is the only way to go and considering the high costs of propane, I cant imagine anyone picking it over Gas if they had the choice.

The two main advantages of tankless gas: Less space used in floorplan. Less standby losses. I dont say better efficiency here because some people (certainly not in this forum) actually end up burning more energy due to the endless supply of hot water.

Perhaps a tank heater's greatest virtue: encourages conservation.

The biggest disadvantage of tankless is the high cost. Rob, I wonder if a water softener is in costco's bid because you better plan for on. This touches on the higher maintenance costs associated with them. You will need to descale the heat exchanger eventually. Ive seen some studies that suggest a MUCH shorter life span with no softeners added which is why most companies require them for warranty. Also, some manufacturers require descaling yearly with a softener. We seem to be drifting from KISS here..

Other Disadvantages of Tankless: Cold water sandwiches, most dont work with low flow fixtures, most arent suited to Solar Water backup, units with pilot flames save no energy, loss of supply during power outages, dependency on an unrenewable resource which many energy efficiency experts feel is better suited to transportation.

Newer models are addressing the low flow and solar backup problems. The only model I know of approved for solar backup is the Bosch AquaStar Model 1600PS.

Back to the issue of cost. Most Independent studies are coming to the conclusion that they are not cost-effective and are showing paybacks of 20 years or more for tankless which is longer than most warranties.
http://www.state.mn.us/mn/externalDocs/Commerce/CARD_Natural_Gas_Tankless_Water_Heater_Study_10051 0053932_DomesticWaterHeatingReport.pdf
Consumer reports take (http://http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/water-heaters/tankless-water-heaters/overview/tankless-water-heaters-ov.htm)

I would also like to eliminate atmospherically vented heaters from anyone's choices. I really hope that readers of this forum have air sealed their homes to the point that these appliances are dangerous. If not, get to work!

The Air to Water Heat Pump is the future of water heating. They are already about the same price as efficient gas units and with efficiencies of 125-300% they are going to make solar water very tough to justify. They certainly are not right for every situation..yet. Soon they will be making split Heat Pump Water Heaters, which should overcome many geographic hurdles. These still face some questions for durability, maintenance and upfront costs. Perhaps its time for a new thread on this..

[Rob Beckers]

Brian, welcome to the forum!

We've had a tankless natural gas water heater for 3 years now (plus about half my life while I was growing up in The Netherlands). You can read about my DIY install in another thread (http://www.greenpowertalk.org/showthread.php?t=5912).

It has worked flawlessly to date. Couldn't be happier with it. There has not been a need for any maintenance on it either. The unit has sensors that will indicate scale build-up, nothing so far. We do have a water softener, since we have very hard well water. Undoubtedly that helps. Though from my time in The Netherlands where we had on-demand water heaters, very hard water, and no softeners, I know that can work just fine too. Every year or two we flushed the unit out with acid, no big deal, cleaned out the heat-exchanger and it would be good to go again. Those units lasted 20 years too.

I agree with your statement regarding finances: The good tankless units (I'm talking gas, the electrical ones are a joke) are too expensive, and installation prices are a down-right ripoff here (Sorry Brian, I know you make your living as a contractor). The savings are small, if you can keep hot water use in check. In my case, I spent around $1,200 doing the job myself. Then got $600 back from ecoEnergy rebates that we had going on at the time. So net cost was only around $600. At the same time I was paying $25 a month or thereabouts for a rental tank-type heater ('inhered' it with the house when we bought the place). Between that and the savings in stand-by losses this water heater has already paid for itself. I recognize though that my situation is somewhat unique, and this won't work for most.

-RoB-

[Paul Bailey]

A Recent article

http://plumbingandhvac.ca/features.cfm?intDocID=1574

[Dave Turpin]

I am considering replacing both my HWH and my furnace with a tankless HWH and a hydronic furnace. It should work; the heaters rated to do this (the Rheem EcoSense 9.4 and the Rinnai condensing) are both 190 kBTu, more than double the current output of my current furnace.

Also, both units will work with solar, since they are designed to only input as much heat as is needed to either provide DHW or to heat the air handler coils to the appropriate temperature.

I am worried about having a single-point-of-failure, however, and DIY seems out of the question because it seems you can't buy the parts from anyone except a certified installer. Also, the electronics involved worry me. These things are not KISS.

[Rob Beckers]

Hi Dave,

DIY works to a point; obviously you can't do much inside these water heaters, but installation can certainly be done yourself. See the link 3 posts before this one of my own HWH install, that too is a Rinnai rated at 190,000 BTU. Saved me a small fortune doing it myself. Be aware though that manufacturers have different versions of their units for space heating and different warranties (at least when I looked at it). They are not all that much different from the regular units, but they run much more often and possibly at higher temperatures vs. just for hot water production.

I hear you regarding the single point of failure. You should know though that this combined use by a single unit is very common in Europe, failures are rare, these things normally last a long long time. Either way, when something happens and you don't have hot water, or heating, combined or separate, you want it fixed fast. As long as you have a good place to call for service that shouldn't be an issue.

-RoB-

[Paul Bailey]

Hi Dave : What is your design heat load/Loss. :idea:

[Dale Sheler]

As kind of an offshoot of Paul's ice house post, I have always wondered what would happen if a guy were to dig a big ole hole, just for kicks say a 40K gallon hole then line it with about 24 inches of styrofoam sides and bottom then use epdm roofing rubber to seal it all up.
You could run a serpentine "duct" of DWV PVC pipe through the "Tank", fill it up in the fall and let it freeze into a solid block, you could use your pvc duct to circulate the outside air through it to ensure it would freeze solid.
After it freezes solid you would super insulate the top, then when the dog days of summer roll around you could simply circulate air through your pvc duct into the house.
In this part of Michigan there are usually four to six weeks when you need air conditioning.
I know of several ponds in the area that are five to six feet deep that regularly freeze to the bottom.
Crackpot or not?

[Dave Turpin]

Sorry I have been out of touch for a while, but work and other projects have kept me very, very busy.

We now have triple-pane windows and R19 Airkrete insulation in all the walls, and our basement is now a master suite.

After our tax return this year, though, we have decided to go ahead with the Tankless/Hydronic furnace installation.

I have not done intensive engineering and heat load calculations, but my current furnace is approximately 70,000 BTU, and since the insulation and air sealing improvements is now more than sufficient to heat the home. Now I have issues with excessive moisture!

The Tankless water heater I have selected is the Rinnai Condensing 199,000 BTU model (indoor, natural gas), which is rated at 96% thermal efficiency. It was about $200 more expensive than the 80% efficient non-condensing model.

Condensing means most of the waste heat from the exhaust is used to pre-heat the incoming water. Assuming no solar pre-heat, this means the exhaust coming out of the unit is actually cool, enough so that the exhaust pipes are ABS plastic!

The air handler I have chosen is the Rinnai 75,000 BTU model. It has nearly the same footprint as my current furnace and is more than sufficient to heat the home.

The beauty is that I am replacing two gas appliances with one, so even though the max usage is 199,000 BTU/hr, I will not need to upgrade my gas meter. This would not be the case if I installed the tankless water heater and kept the old gas furnace.

The Rinnai tankless water heater and air handler work together to select the proper water temperature. When the house needs to be heated, the heater produces 160 degree (F) water, and drops it to 120 (F) for domestic hot water. Also, if you use hot water in the house, the furnace automatically switches off during the use. (Actually, the fan will stay on for a minute if you are just using a sink for a moment)

I am also installing a whole-house air cleaner and electrostatic precipitator, and upgrading much of the HVAC. One of the major inefficiencies in my HVAC setup currently is a lack of return ducts. There are 8 heater ducts but only one return duct in the center of the house... So the extremities get cold. I am installing additional returns in peripheral rooms to minimize temperature variation.

I will have pictures of the installation when I start to do the work!

[Rob Beckers]

Hi Dave,

I'm somewhat on the same path as you, though I've not made quite your progress yet! As you probably read in another thread on the forum, I've installed a Rinnai myself (http://www.greenpowertalk.org/showthread.php?t=5912). Can't believe it's already 4 years ago! The unit is still going strong. No issues to date, it just works. My wife and teenage daughter are very happy with it. :evil:

Mine is a regular 80% efficient unit; at the time the condensing ones were a king's ransom, and since we were not going to heat the house with it, the expense didn't make sense. I like your idea of the condensing unit doing double-duty. When I lived in the Netherlands I had a similar unit (hot water and house heating in one), though only mid-efficiency. We're talking 25 years ago though...

I've also had triple-pane windows installed, about two years ago (or is it three already?). The calculations I did at the time showed windows don't pay for themselves, not if you still have decent ones. In our case we didn't have a choice, the old ones were rotted out (alu-clad wood, only 20 years old), and we got a nice rebate from the ecoEnergy program we had at the time. The new windows solved the massive air leaks around the frames (used to be plugged with fiberglass bat, now it's foamed in), and the rooms are noticeably more comfortable now.

I did install an electrostatic whole-house air filter 7 years ago, right after we moved into this house (did the job myself). It's actually a combo of harmonica/paper filter cartridge and electrostatic cleaner. The filter gets replaced once a year, and they are quite cheap. Consumer Reports tested it at the time as the most efficient one on the market (in actually removing micron-sized particles). It's hard to evaluate how well an air filter/clearer works, I'm assuming it's doing its job. It's an Aprilaire 5000. Good brand (I also installed their whole-house humidifier), I can recommend it.

If you're having moisture problems be sure to look into a heat-recovery ventilator. Moisture can do a lot of damage (also to your health!) without being all that visible.

Please post more details/pictures as you continue your home improvement quest! I would also appreciate a little more info regarding Airkrete, how that is used as a retrofit. One of my problems is that this house is leaky as a sieve, despite the many holes I've plugged it continues to leak air at an alarming rate (so humidity is not a problem, in fact, quite the opposite)...

-RoB-

[Dave Turpin]

The Airkrete is foamed in with a fairly small nozzle. My exterior is brick over framing, so the installer drilled 3/4" holes, 3 high, spaced every couple of feet. They drilled through the mortar and then the wood.

They foamed from the outside while another guy was inside with his ear to the wall making sure the wall was filled, but not too much. They said it was entirely possible to pop the plaster off with too much fill.

Now, my walls previously had no insulation, but they also said even if fiberglass in there, the Airkrete pushes it out of the way. I got R16 with 2" of fill (geometric constraints)

They also quoted me a job to vacuum all the rock wool out of the attic and foam in R30, but it seemed expensive at the time. :laugh::

[Russ Bailey]

HRV units are great - we installed one and love it. A good unit is in the 70% efficient range for heat recovery and we have not had any problems with mold at all - the house is concrete and block so is a bit too airtight to do without the HRV

[Dave Turpin]

Before I install one of those I am going to see how replacing the furnace does to control moisture. A hydronic furnace produces no byproduct water, so theoretically it should be much drier in the house.

I just hope that it isn't such a large shift that it affects all the hardwood in my house.

[Dave Turpin]

I have installed the Rinnai tankless and the Hydronic air handler. I will post the installation details in another thread.

I did learn a couple things, though, that i think are pertinant here.

1) The system totally works, even in its current "less than ideal" arrangement. (more on that below) It heats the house beautifully and seems to flow a lot better than my old system.

2) Passing inspection was not as tough as I thought it would be. However, you need to be ready for the inspector to show up AT ANY TIME on the day you requested. Because my guy showed up at 0700 and I was not on the drop yet. He came back 10 hours later.

3) I had a serious misconception on how the Rinnai hot water heater and Hydronic handler work together. Specifically:

-Contrary to my previous belief, the Rinnai tankless unit will NOT produce different water temperatures when using as DHW vs. hydronic heating. So, if you set it for 120F/50C, it will heat the DHW to 120F/50C (ideal) but will also heat the hydronic to 120F/50C (not ideal, and definately not 75000 BTU/hr at that temp!)

-On a similar vein, but good news: You can use DHW (within reason) whilst simultaneously heating the home. The handler only shuts off if you are using the max output of the water heater for DHW.

-The BTU/hr rating of the air handler is based on supply water at 150F/65C. You cannot get the water to this temperature with the Rinnai tankless unless you install the RCC-91 temperature controller. Doing this also reduces the warantee of the water heater to that of a commercial installation! However, it is possible (by flipping a switch inside the water heater) to heat water to 140F/60C. By my calculations, this will produce 72,000 max BTU/hr, which is still more than sufficient for my installation. It is something to keep in mind, however, if you are selecting a handler with a small "safety margin"!

-Now, something that was not adequately covered by the manual that I read, (and since I was under the assumption that DHW and hydronic heating were handled by seperate controller algorithms), in order to do all this correctly and NOT burn the living crap out of yourself, you MUST install a tempering valve in the system, to reduce water temp coming out to a safe temperature. I did not do this, but now that i know, I have ordered one and it should not require too much more plumbing to install.

Fortunately, heat transfer being constant, heating water to 140F/60C and then mixing it with cold water down to 120F/50C will still produce the exact same 9.8GPM/37.5LPM DHW flow rate at the tap, and, according to the specifications, should be at the same thermal efficiency.

Another thing I neglected to do was to install an Air Trap, which I later discovered is required per the installation instructions. I managed to purge the air from the heat exchanger, but I also ordered one of these and will be installing it.

Oh, one more thing. This may not be required in your area, but in mine an apparatus called a "condensate neutralizer" was required since the condensate from the water heater is so acidic. This is only needed for the high-efficiency "condensing" hot water heaters. Nobody produces these devices anymore, so I had to make one myself. It is basically 2" PVC, with 1/2" inlets and outlets, and removable caps, plumbed into the condensate drain line heading to the sewer or sump. Fill this with crushed marble or limestone and refill once a year. Mine is filled with a smashed piece of travartine I had lying around.

[Ralph Day]

Sounds like a nice installation Dave, I look forward to seeing the pictures and such.

I'm surprised you got an inspection go-ahead without the tempering valve. I thought they were standard requirement in any inspected plumbing work nowadays.

Ralph

[Rob Beckers]

Thank you for the information Dave!
I've been looking at a similar setup as yours for a new business building that I'm working on. It's good to hear the 'gotchas' beforehand. One question though: Isn't your Rinnai rated at 199,000 BTU/hr? So why the 72,000 BTU/hr?

Did you look into the commercial controller at all? I'm wondering if it allows for different settings depending on the need (DHW or heating). Probably not... It would need to have some input that gets toggled by source.

I'm currently dumping the condensate from my high-efficiency gas furnace in the sump hole (no lime is being harmed in that process), where it gets mixed with all the other water coming in. Since we live in a swamp I doubt it makes any difference to the overall PH.

Lastly, we want pictures! It didn't happen unless there are pictures! :nuts:

-RoB-

[Dave Turpin]

Pictures coming soon!

Oh, and when I said I had passed inspection, I have only passed the gas line inspection and the rough-in inspection. The final inspection is scheduled for a few days to close out the permits. I have more than just the new water heater on the final inspection, though; I have a whole new bathroom.

From what I understand about the commercial controller, all it does is allow higher temperatures. You would still need a tempering valve, which in this case would have to be a commercial unit that was rated for high inlet temps.

The water heater is rated for 199,000 BTU/hr but the air handler itself only uses 75,000 BTU/hr. You can also get a 90,000 BTU/hr unit. You could run two of those, actually, if you had a big house to heat.

This actually means you can heat the house whilst simultaneously taking a hot shower and running the dishwasher.