Installing an on-demand water heater

[Rob Beckers]

Some time ago we discussed the pros and cons of tankless on-demand water heaters in this thread (http://www.greenpowertalk.org/showthread.php?t=2646). As I mentioned in there, my current tank-type water heater is a rental, and rather than continuing to subsidize the owner I wanted to change it for an on-demand water heater. This should also save some energy (and $$) in the process. That time has finally come, and this thread chronicles the process. I realize that an on-demand water heater still uses fossil fuel (natural gas in my case), and is therefore not exactly green. Still, it uses less than a comparable tank-type heater, and it may be of interest to others. Hence this thread.

The current (old) water heater sits in my basement, a rather cramped area with barely enough headroom to stand (my head ends up between the floor joists above). Not the greatest place to work. The new water heater is supposed to go between the two studs behind the old water heater. While not visible, there is already a 6" hole in the concrete foundation wall in that area (through 10 inches of concrete). One of those black pipes is a sewer line, so the new unit will have to sit some distance away from the wall, to clear that pipe.

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=72

The original plan was to buy a Rinnai R85i on-demand water heater. It turned out that model has been discontinued, making the nearest Rinnai replacement the R94Lsi. I have purchased one of those, together with a vent kit and a plumbing kit (this makes it easier to flush out the heat-exchanger when needed).

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=73

This water heater is a direct-vent unit; meaning it draws its combustion air from outside, and vents outside. That is a good thing IMO, as using inside (heated) air for combustion means wasting energy by drawing in cold outside air to replace it. Rinnai uses a proprietary vent system of co-axial vent pipes. The inside metal pipe is the exhaust, the outside plastic pipe draws in combustion air.

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=76

In case you are wondering what the inside looks like; it is full! Every bit of space in there is crammed with plumbing, wires, and electronics.

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=75

That is all for now, as an introduction. Yesterday I purchased some wood to frame out a place to hang the water heater, and copper bits and pieces to plumb the unit into the water lines. Hopefully I'll find some time in the next day or so to hang it on the wall. Then the wait is for the gas guys to hook it up to the gas line. The current water heater is on a 3/4" gas line, and that is too small for the on-demand heater. It will need a 1" line.

More to follow...

-RoB-

[Ralph Day]

Congrats Rob, on going tankless.

My one input would be to be sure to hook up any anti-freezing setups on the unit. If the unit is near it's exhaust outlet then cold air may infiltrate through the exhaust stack or indeed through the input piping. Your winter temps in Ottawa will surely freeze things if there's not a heat source on the heat exchanger.

My Takagi almost froze in it's first winter -25c. The Z duct conducted cold into the heat exchanger (and the anti-draft baffle let cold air backfeed through the unit somewhat too). Luckily, I caught it before any damage was done...at the slush stage only. Freezing the heat exchanger or pipes were not warranty covered. There are some little block heaters on the Takagi which used about 2kw per day when operating! Solved the problem by ducting a fan blowing room air through the unit and out the exhaust stack.

Good luck with your installation.

Ralph

[Rob Beckers]

Hi Ralph,

The Rinnai unit has build-in freeze protection: If you look at the picture that shows the insides you can just make out two white resistors on the left side that are tied to the heat exchanger. There are several more in there, not visible on the picture. In all they make a 100 Watt heater that comes on automatically when the heat exchanger temperature drops near freezing. Hopefully this won't switch on too often, as you note it can add up quickly in electricity use. I'll put it on a Kill-A-Watt in the winter, during a few really code days, that should tell.

The unit also comes with a condensate collector and drain build into it. Another good thing to have in a cold climate. All I need to do is hook up a hose to it, no extra parts needed. The vent pipe needs to be angled just a little so it drains to the inside to make this work.

Meanwhile, I'm waiting for one more 10" piece of vent pipe. The 21" standard horizontal vent kit is just a few inches too short; There's 10" of concrete to go through, 4" of framing and insulation in front of the foundation walls, 6" to stay away from the sewer pipe, 1" offset of the vent pipe from the back of the unit, and about another 1" for the plywood that the unit gets screwed onto.

-RoB-

[Paul Bailey]

Good Choice on the Tankless Rob: I've read nothing but good things of Rinnai ,Takagi, and Noritze Tankless units. The savings of going to any tankless are well represented as compared to ANY tank type storage, plus all the extras as well.(space savings,remote temp control). Yes there alot of $$$, but the savings begin from day 1. If this unit (Rinnai)had been somewhere between the house and the NEW shop it could very easily heated Both as well as your Domestic hot water (DHW) . ,In either a hydro air or radiant application.:)

[Paul Bailey]

I thought I would add a little pic as how this mess of pipes really looks on a sketch. The polariswater heater (on the left would be substituted with ANY Tankless or other heat source The tank on the right hand side is and Indirect or other storage tank/reservoir .:)

[Ralph Day]

Hi Rob, Paul (any others interested too)

Hopefully your temperature sensors to activate the heaters are in/on the heat exchanger. The TKjr unit's is a thermistor screwed to the outside wall and wired into the unit. When the temp went below freezing, the heaters went on...until the temp outside went above freezing. In our geographic area that would mean the heaters would be on for about 5 months straight @2kw per day=300kws. That's more than my total power production a summer month.

Ralph

[Rob Beckers]

Ralph, yep, the sensor is inside the Rinnai unit. There are no external sensors. Still, I'll keep an eye on it, and measure use on a really cold couple of days this winter.

-RoB-

[Joe Blake]

I have already posted here, but it must have disappeared into that black hole which scrubbed out some data.

(Please pardon if you've already read this before.)

I recently had my HWS upgraded to solar with an electric booster. The booster is only needed for a few weeks of the year, and then only for an hour a day usually, unless there's a very prolonged cold, grey spell.

The solar HWS replaced an electric "on demand" electric heater, which was nowhere near as sophisticated as Rob's new one. One reason for replacing was that it was either too cold, too hot or consumed too much water. It was a "pressure valve" job so in order for the switch to "trip" there had to be a certain minimum water flow. Not recommended in dusty, dry Australia. Further it had three heating elements, without any temperature control. They were either on or off. The only way to regulate the temperature of the outgoing water stream was to add cold water - more water consumed, as well as excessive electricity.

I managed to trace back to the main power board (my house is fitted with 3 phase electricity) and discover that one of the elements had its own phase and fuse, so I was able to remove that element from the heating. Unfortunately, it then only warmed the water instead of heating it. In summer time this was bearable, but in winter, no way. And again, if I'd been able to reduce the water flow rate I may have been able to achieve sufficient heating without excessive heating.

Anyway, when it blew an element, the owner of the house elected to go solar, and not only has my power bill dropped, but my water consumption has reduced even further.

Just as a note of historical interest, in Western Australia internal combustion heaters (gas fired) were banned, and had to be installed externally. This was because of a few cases of carbon monoxide-linked accidents/ deaths. Australia doesn't have a penchant for building houses with cellars so that option is not available to us.

Joe

[Rob Beckers]

The Rinnai is hanging on the wall. All I can say is "don't try to do this by yourself". The sucker is heavy! :eek: Trying to balance it on the wall at the right spot, keeping it there with my head, while driving a screw, does not work too well (I had put the lower bracket in place first, so it had something to 'sit' on). A few extra hands would have been very useful, but at 6am my better half was still sleeping.

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=77

Just used a few pieces of 2x6, screwed together, to shim out sufficient distance from the wall to clear the sewer drain. A piece of plywood on top as a base to screw the unit onto. I've got enough screws in there to keep a house up, should be bullet proof.

The vent pipe is running at a slight angle, so condensate drains to the inside of the house. There's a condensate drain on the unit that I'll hook up to some tubing, into the (nearby) sump hole. Talking about vent pipe: The extra 10" piece arrived yesterday. That was needed to get enough clearance on the outside of the wall. The standard 21" vent pipe didn't cut it due to the sewer line that is in the way. The vent pipe is foamed in using some low-expansion PU foam (still had a half-full bottle sitting here). On the outside there's a trim piece, comes with the vent kit, that will cover up the hole.

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=78

Tomorrow I'll call the gas guys to schedule the installation of the 1" gas hookup. The plan is to have them come in the morning, so I have all day to work on the plumbing. Then we keep our fingers crossed that it works! If not, we'll all be taking cold showers for a while, since the old water heater will have to be moved out of the way and disconnected to hook up the new one.

-RoB-

[Rob Beckers]

So much for the gas guys: The company I normally use for this type of work tells me they won't connect appliances that they did not install themselves. The same company had quoted me $3,200 to install this same water heater, compare that to the $1,200 I have invested so far in materials... :der:

Meanwhile, I have hookup up the water pipes to the heater. For now, it is connected in parallel with the existing tank-type water heater. Hopefully I'll be able to get the gas line hooked up in parallel too, so I can use the new water heater for a little while to make sure it works and is reliable. The alternative, not having hot water, is going to upset the rest of the household.

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=79

I have installed isolation valves on the Rinnai, these are two-way, so I can hook up a hose and flush out the heat exchanger if needed. With the water softener we have this should not really be an issue, it is mostly for places that have hard water (and no softener). The valves also let me use this heater in parallel with the tank-type water heater (it has a valve too, so I can select which one gets water flowing through).

While I admit that I'm not the world's greatest plumber, I have done my share of soldering. The part I seem to never get to work right is the sealing of NPT (threaded) fittings with teflon tape. No matter how many times I try; a few turns of tape, lots of tape, coupling torqued up tight, or not. In 2/3 of all connections I cannot get it to be completely watertight. Here too, the best it has gotten is so there's a drop of water coming out about every minute. :frusty: Does anyone know the secret to watertight connections with teflon tape? :help: I have bought a little tube of pipe dope, that will be my next attempt. Word has it that it is easier to get watertight connections with dope.

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=80

While I was at it, I also fixed a shortcoming of the existing plumbing: We are on a well and get quite a bit of sediment, even sand, coming up the pump. That is not good for things like water heaters and water softeners. So I have installed a sediment filter. This is somewhat different from the usual cartridge-type filters: It has a permanent stainless steel mesh. The big green knob on the bottom-right opens up a valve in the bottom, and it causes the filter to backwash itself. Depending on the amount of sediment this needs to be done every now and then. The filter is a Honeywell/Braukmann F76S. It comes by default with a 100 micrometer mesh, and they sell mesh sizes down to 20 micrometer (with the sediment we have that would likely clog too fast though). It is a bit more expensive upfront, but there are no replacement filters to pay for in the long run.

That's the progress to date. Tomorrow it is back to finding a gas fitter to get the Rinnai hooked up.

-RoB-

[Paul Bailey]

Rob : Dope /tape/ Dope in that order. Small amounts of the dope as it will kind of mush out anyway.:)

[Ralph Day]

Paul, dope and tape? Rob is talking about plumbing joints...:nuts:

I went to dope, the kind with a brush on the can's lid. It's mucky but never a leaky fitting with it. Tape always drove me nuts!

Ralph

[Rob Beckers]

Paul's method seems to work: I've replaced the 3 leaky joints with teflon (lots of it) plus a small amount of pipe dope on top of that. So far they are holding! :cheer2:

I had a gas fitter over today to look at the job of hooking up the heater to the gas line and mentioned my teflon tape problems. He mentioned that plumbers use pink teflon tape, apparently that is much thicker than the Home Depot stuff. Using dope over tape didn't seem unusual to him, though he usually didn't use dope for that kind of joints.

-RoB-

[Rob Beckers]

My gas guy, Mike, showed up yesterday to hook up the gas line to the new water heater. So, it has finally happened: The Rinnai is working! So far it's only been a few showers. Nothing special to report, it just works as advertised. I have set it to 120F, and if anything that seems to be a bit warmer than the water coming from our old tank-type water heater.

For now the old and new water heaters are hooked up in parallel. Both are on the water lines, both have a gas line running to them. Simply opening up the gas and water valves switches on on and the other off. I will leave it like that for a few weeks to make sure the Rinnai is working reliably, and then disconnect the tank-type heater (and tell the Direct Energy to come pick it up, since it is a rental).

-RoB-

[Rob Beckers]

Now that this project is complete, here are the last pictures of the (working!) water heater. It works really well too: Switches on with just a little bit of water flow, and is so quiet you have to get really close to hear if it's working or not.

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=87

It is amazing what they manage to cram in that little box. Especially when one considers that it is much, much larger in terms of BTUs than the big furnace that heats the house. Considering how tiny that heat exchanger is in the water heater, it does a pretty good job at 84% efficiency (anything above that and you get a condensing heater, and things get much more complicated).

http://www.greenpowertalk.org/picture.php?albumid=4&pictureid=88

So far, so good. I can go back to my favorite activity...:couch2:

-RoB-

[Joe Blake]

Bewdy.

Just in time for the depths of winter?

Nearly November, and it's raining, cold, had Donner und Blitzen last night. And this is supposed to be summer!!

Climate change? There ain't no such thing.

:notrust:

Joe

[Rob Beckers]

Howdie Joe!

They've been promising us another long, cold, and snowy winter this year (something to do with El Nino, or La Nina, not sure what cycle we're in). Boy did winter start early this year: We had 11 cm of snow last night, and another 5 or so on the way today. Wind is blowing like there's no tomorrow (do I wish I had a wind turbine now!). I rushed to get the snow tires on my wife's car yesterday, so she can get to work this morning. Timing is bad: I have a big truck coming today to pick up a wind turbine for delivery to a customer, and my forklift doesn't work too well on snow. Slick little tires, no profile on them.

But, the hot water is hot. So all is still well.... :peace:

-RoB-

[Rob Beckers]

It has been a few weeks, so time for an update on the on-demand water heater. As you may recall, I left the old tank-type heater in place (simply switched off the water and gas supplies to it) so in case of trouble we could switch back to it in a jiffy. That has not been needed, the new water heater has worked flawlessly. More importantly, management (a.k.a. my wife) could not be happier; no more running out of hot water!

For the most part we can't tell the difference between tank-type or on-demand, both just work and there's hot water. For those contemplating the switch there is one difference that may or may not be of importance: When one has tapped hot water, then switches off the tap for a little while, there will still be hot water in the pipes the next time the water is switched on again. However, the heat exchanger in the on-demand heater will have cooled off, and it will take a little time (10 seconds or so) for it to heat back up. So, the result is that after that left-over hot water in the pipes there will be a period of 10 or so seconds of cold water, before the temperature goes up again. A tank-type water heater does not have this. For us this is a complete non-issue, I just mention it since it may drive others up the wall.

So, the plan is to finally disconnect the old water heater some time this week, and call up the owner (the gas company) to come and pick it up. It is a rental, costing around $20 a month (plus tax) in rent. That is one reason why the additional cost of an on-demand heater is well worth it for us.

-RoB-

[Joe Blake]

To save the water


http://www.abc.net.au/tv/newinventors/txt/s1389495.htm

Joe

[Ralph Day]

Hi Joe
Good water saving tip from down under. I suppose if you have to wrestle every drop/pay for every drop, it is wise to save every drop you can. Here in my area the only reason to be a water miser is to decrease your water heating budget, not save overall (yet). Things are changing. Rumors of metering well water usage (akkk!), I'd just use my rain captured water.

One evaluation i have yet to do is the daily consumption figure comparing my submersible Grundfos pump and my Dankoff booster pump (from the cistern). I can run the entire house on either system or isolate the well water for just drinking (like right now) and run all else off the booster pump. The booster only uses 60-70 watts when running while the submersible uses 900 watts. Need to see a total daily figure running the house on each system seperately but will require putting an outlet plug on the Grundfos control box to allow use of the Kill-a-watt meter. Maybe soon.

About 4 inches of white material all over the ground, panels and roads. Apparently you can;t remove this stuff from the roads (at least I haven't seen anyone doing so this morning!) It costs a lot of money to plow and sand the roads, but it's cheaper than law suits people might bring against the municipality for not doing it. If only people could remember how they drove last winter during the first storms of this winter.

Ralph

Ps edit: Rob, just don't jump into the shower until the hot water has stabilized...been there, done that!

[Rob Beckers]

With the outside temperature at -21C I measured stand-by use of the Rinnai. Main reason was to find out if it is kicking in its anti-freeze heater. This was mentioned a number of posts back: To protect the heat exchanger the unit has a few large resistors (total around 100 Watt) that get switched on when the heat exchanger temperature gets close to freezing. This would happen if cold air enters through the vent pipe.

I am happy to report that even after letting the unit cool down there seems to be enough heat from the basement getting in to keep the heat exchanger toasty. A Kill-A-Watt meter shows its stand-by use as 1 Watt (!). Now, I do not have much confidence in the accuracy of that meter at such low power levels, so it may be a few Watts more, either way it is not much.

-RoB-

[John Canivan]

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here is another option.
Johnny Solar

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