Tankless Water Heater as Heat Source

[lrrowe]

While I do not have my CT yet (I know which one I am going to order) I am collecting all the ideas and information I can get for the "things" to add to it.

Here is a new one I believe. I currently installed all by myself, a hydronic radiant heating system in my house using pex tubing and a large efficiently water heater/boiler. At the time I was considering looking into a tankless water heater as the heat source but could not find enough encouraging support for this method. But it is done.

So I am now wondering, why could not this be done in a CT? Either by running the water through "fins" like in a home baseboard system or through a large heat exchanger like the ones used to put radiant water heat in your air handler (or even a radiator of sorts).

Having become a adequately self trained radiant heat installer I learned a few things here and there on this matter for homes and I am sure I can easily learn more. To move the water, there are 120V low Amp pumps, but I do not know about 12V. More research needed. Along with research on all the other obstacles (thermostat, holding tanks, water deverters for showers and the like, etc, etc).

But think about the safety aspects for heat with this idea. Keep the tankless heater outside and no carbon dioxide issues at night. Might only need a low electrical current to circulate the hot water.

Has anyone given any thought to this?

Now if I can convince the CFO that she will like the CT, I can get moving forward.

[MtnDon]

My plan is to do a similar thing. I am thinking along the lines of pumping the heated water through a finned assembly like an auto heater core or a auxiliary transmission oil cooler. Probably a tranny cooler as I have a couple NOS sitting in boxes on a shelf. Put it in a box/ducy and then use a small fan to circulate air through the core; there are some computer fans that are very quiet. Small 12 VDC pumps are available.

http://www.amazon.com/dp/B005EU7ONM/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=1AUD4PWVH507A&coliid=I2U32TJIBFFBFH

If you click on the image in that link that will bring up larger images with full pump specs. You can find lots of cheaper ones on ebay; direct from China. I may try one of them.

As for heat source there is one thing I don't like about on demand tankless heaters. Most are a pain to drain and drain well enough if you need to worry about freezing weather. I know a couple people who have had their on demand heaters freeze and crack the metal tubing even though they blew them out with compressed air. That is my main beef with them. I will be using a std RV water heater, a Suburban or an Atwood in 6 gallon size. I prefer Atwood but they are wider and won't fit thru the std wall rib spacing on a CT without modifying one rib.

Thermostat? Haven't thought that far ahead. For pure simplicity maybe a wind up timer switch. That would be akin to tossing some wood in the wood stove and letting it burn out. If well enough insulated and not camping in - 20 F temperatures that may be good enough.

[lrrowe]

MtnDon, is the link correct? I could not see how to use it?


This likes similar to what you are going to build with the equipment you have already.

I understand the issue with freezing and wondered about the draining each time you are away from it. One model has a freezing protection circuit which draws less then 1 amp 120 AC. Could work if you have a way to keep a battery recharged when off the grid.

I will have to look more into the heaters you describe to see how available they are from scrap/recycling centers.
Bob

[MtnDon]

Sorry I screwed it up. I fixed it.

[lrrowe]

Thanks,
I had already gone to ebay and found similar pumps at greatly reduced costs.
I think your idea of a built in hot water tank may be better then my Instant Water heater idea. Certainly drainage in case of freezing is not the same issue as long as you keep gas flowing to it. During down periods you would have to either leave the gas on (not so good) or drain the water.
If I were to go with it, I would think about air valves so it would be easy to blow the water out with a compressor.

I also looked at the Suburban and Atwood heaters you mentioned and I now think I will leave towards them. I do not have the left over coils as you do, so either I would have to add another "DIY" project to my list or just buy the much higher priced heat coil assembly.

Another reason I like your idea is that the 6 gal. water tank is a built in reserve tank that that is not in the Instant heater system unless you add it (another expense and level of complexity).

Now if you want to get wild, you could start thinking about solar water installation to reduce the gas consumption. But this would be getting too complex for one who wants to keep a relatively simple system.

Bob

[MtnDon]

Yes that looks like a nice unit. I'd try to emulate that.

One model has a freezing protection circuit which draws less then 1 amp 120 AC. Could work if you have a way to keep a battery recharged when off the grid.

From my off grid cabin experience, any form of heating that uses a resistance heating element is difficult to execute well without a very large battery bank. 1 amp at 120 VAC becomes 10 amps at 12 VDC. It's the dark hours of the day/night that are the problem and that's when it is likely to be coldest. We enough battery capacity at the cabin that we can run toasters, coffee makers but that's with 900 pounds of batteries.

I gave up on the idea of any long duration resistance heating with smaller system as in a trailer. I also hate generators, even my quiet Yamaha, so that contributes to my avoiding resistance heating in my trailer plans. I will have a 2000i, but hope to never need to reply on it.

[Prem]

I had a tankless water heater in my bus conversion with a heat reflector that vented to the inside of the vehicle. They used to come with either a heat reflector or a duct for taking the exhaust outside. The vehicle was voluminous. Since it only kicked on when someone was taking a shower or drawing dish water, the heat gain was undetectable. Mostly, the device was just a headache. We got to the point (quickly) of just heating water for dishwashing on the propane stove. I had to have all the bells and whistles, that's why I installed it in the first place. Parked on the beaches of Baja (three family trips), we all ended up with the solar-heated camping shower bag in the palapa draining to the sand. (Biodegradable shampoo and soap.) It was just so easy that way and no maintenance. I drained it for the winter just by leaving the hot water faucet open on the kitchen sink (lower than the water heater) over night. Drained it fine.

The tankless water heater was only good as a selling point for the fellow I ended up selling the rig to years later.

[MtnDon]

We use a Suburban SW6P heater at our cabin. I selected the pilot light model for a few reasons. 1. when on pilot only it provides all the hot water we need for normal use. The tank has an extra 2 inches of insulation all round. That greatly reduces gas use. 2. In cold weather it keeps itself warm enough to not freeze. 3. It is easy to isolate with a Camco bypass kit and that 4. makes it easy to drain. For some of the cold months we leave the tank isolated and empty but use the cold water system. That is also easy to drain and blow out with the built in fittings/valves I used.

Atwood heaters are lighter and IMO their burner and heat transfer system is more efficient. But it is wider with the tank long dimension parallel to the wall instead of perpendicular. Also cheaper.

[OverTheTopCargoTrailer]

[lrrowe]

Sorry Jerry, I do read your inputs (will not call them junk). I just do not recall seeing it before. But "blush", I did not do a search first. I will humbly do that now.

Bob

[OverTheTopCargoTrailer]

[lrrowe]

So are you saying that you basically have two tanks of hot water radiating warmth to "heat" your trailer.?

[bdosborn]

Most are a pain to drain and drain well enough if you need to worry about freezing weather. I know a couple people who have had their on demand heaters freeze and crack the metal tubing even though they blew them out with compressed air. That is my main beef with them.

Hmm, it's amazing the things you pick up on this forum. I'd been looking at these for our cabin but I probably won't anymore as we shut ours down in the winter and drain the water system.

Bruce

[bdosborn]

My plan is to do a similar thing. I am thinking along the lines of pumping the heated water through a finned assembly like an auto heater core or a auxiliary transmission oil cooler.

You might want to check and make sure they don't use lead solder or something like that if you're going to run potable water through it. It's probably fine but it's something to think about...

Bruce

[OverTheTopCargoTrailer]