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bldginsp
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# Posted: 9 Mar 2014 02:48pm - Edited by: bldginsp
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This thread is for anyone to add your experiences/learning to help out others just learning about this subject. It's a subject that has come up a lot, and there are lots of things to know about off grid water heaters.
Here's what I've learned:
Electric is possible, but for off-grid, propane is the usual solution. Here's a summary of the different design options I've found available on these propane on-demand water heaters:
-Ignition. Most models manufactured use 110v power, so you have to find one that doesn't need this. Options are pilot lights, batteries, and some have hydro turbines that ignite using water flow when you turn it on. These last ones are more expensive.
-Flu. Either you choose an outdoor unit that exhausts out the side of the unit, or choose an interior unit that exhausts with a flu. Outside and inside units can be subject to freezing, see below. Inside units with flus need to account for combustion air, see below. There are two types of flus used, stainless steel and galvanized 'B' vent. The stainless are used, I think, only on 110v units that have a fan to blow the gasses out thru the flu. Units without 110v will use natural draft to exhaust the gasses, and can use a galvanized 'B' vent. Don't put a B vent on a unit that requires a stainless vent. The 110v units are generally higher efficiency, and produce corrosive chemicals in the exhaust and will corrode a galvanized vent. A natural draft vent must be installed carefully so that it will draft. It needs a certain amount of vertical distance of flu to operate correctly. Stainless vents are expensive, B vents are not.
-BTUs. On demand water heaters can only heat so much water at a time, since they have no storage. A 200,000 btu unit will operate two, perhaps three showers at once. A 75,000 btu unit will probably operate only one.
-Freeze protection. The heating element in an on demand water heater traps water when not in use. Even if you drain the water pipes, water will stay in the unit. Same is true of a shower mixing valve. If that water is there during freezing temperatures, the element will be damaged. This is true if you mount it indoors, or outdoors. When you plan to leave the water heater where it will be exposed to freezing, it must be drained. Some units have drain plugs for the purpose. Shower mixing valves do not. One solution is to blow compressed air thru the entire system before you leave to remove all water. Another solution is to mount the heater so it can be easily removed and taken home.
-Combustion air. If you mount the unit indoors, it must get enough air for the gas to burn and for the natural draft vent to operate correctly. If you have a woodstove, it will be pulling air out of the cabin as it burns, which creates a negative pressure in the cabin. This can cause the water heater to not get the air it needs to burn and draft. It can also cause cold air from outside to be dragged down the flu onto the element, freezing it. One solution is to place the water heater in a sealed closet with a weatherstripped door, so it is separated from the air in the cabin. In this case you need to install combustion air ducts to the outside of the building to supply enough air for burning and draft. The instructions will tell you how large these ducts must be. The building codes require that a water heater installed in sleeping areas of a house be located in such a sealed closet.
-Adequate propane. These units use a lot of propane in a short time. When propane gets lower in temperature, it does not flow out of the tank as quickly. At minus 40F (or so) it stops altogether. So, a standard 5 gallon (20 lb) propane tank might not operate your 100,000 btu water heater if the propane is at 0 degrees. You might need to have two 40 lb tanks instead of one 20 lb, just to get adequate flow. If you are using a propane wall heater at the same time the problem is increased.
Gas pipe sizing. Because the units use a lot of gas in a short time, the size of gas pipe is important to assure proper flow. If there is very little distance from your propane tank to the heater it's probably irrelevant, but if you have a 120,000 btu water heater and a 80,000 btu wall heater, and one of the appliances is 30 feet from the propane tanks, 1/2" gas pipe won't work. Gas pipe sizing is a bit complex, again only important when the gas pipe is long. Here's a link to a gas pipe sizing chart, but be aware that gas pipe sizing invovles more than just looking up something on a chart:
http://www.engineeringtoolbox.com/propane-gas-pipe-sizing-d_827.html
-Calcification. On demand water heaters will build up mineral deposits quickly if your water is hard, as from many wells. There are procedures for removing this, it must be done or the heater will eventually fail to heat the water enough. Probably a good idea to plan for this at installation, so you can arrange your piping accordingly.
-Brands- Eccotemp, Bosch and Marey are three manufacturers that make off-grid capable on demand water heaters. Check prices on Amazon and elsewhere, and read the installation/use instructions on any unit you consider buying to be sure you understand all its features and requirements before you buy.
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Dekagoldwingers
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# Posted: 9 Mar 2014 06:48pm
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This a a Great Checklist. Thanks
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Hunterda
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# Posted: 15 Oct 2014 09:25am
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What an amazing post! Thanks
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Ontario lakeside
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# Posted: 16 Oct 2014 01:13am
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We use a ecotemp at our off grid cabin. I have a video of the system for those interested.
https://www.youtube.com/watch?v=funUNu9zVLQ&list=UUGuSGWaR9LgZwYVvaE3sXIA
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bobrok
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# Posted: 17 Oct 2014 08:36am
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We opted to use a 6 gal. RV heater by Suburban. I know there was some previous conversation about code regulations not allowing these installations in some places, but it seems to be prevalent in my area so we went with it.
Anyone know about code requirements on these?
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bldginsp
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# Posted: 17 Oct 2014 09:02am - Edited by: bldginsp
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I don't know, but in general, the code allows any piece of equipment to be used only where the manufacturer's instructions allow it to be used. When a manufacturer makes something, they have to get it approved by UL or another listing agency like them. Then, the building code allows the equipment to be used only where the equipment was tested to be used by UL or Warnock Hershey or whoever. In this case a piece of equipment listed to be used in an RV is not listed to be used outside of an RV and probably would not be allowed by the jurisdiction. Doesn't mean it can't be used safely elsewhere, but it does mean that you have no instructions for how to use it safely outside of the RV, because UL didn't test it for that use and the manufacturer didn't provide instructions.
Hope this makes sense, it's the basic logic of how the codes approve or disapprove equipment, from woodstoves to water heaters.
Anyway, what kind of heater is this? Electric? Propane? Do you have an instruction manual for its use, or for its installation?
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MtnDon
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# Posted: 17 Oct 2014 09:24am
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Correct bi. RV water heaters are approved for RV's and that's it. You may find an inspector that could permit use in a residence, but most cabins using RV water heaters likely never had an inspection / approval. I believe the installation can be safe though. One point is RV water heaters are not very energy efficient; maybe okay for part time use.
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bldginsp
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# Posted: 17 Oct 2014 10:06am
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Seems like there should be a very small propane water heater approved for use in buildings, but maybe not. If anyone finds it, let us know.
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MtnDon
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# Posted: 17 Oct 2014 10:19am - Edited by: MtnDon
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I've looked many times and there is no small and residential approved tank type water heater that I have been able to find. Maybe something to do with being able to design an efficient heat exchanger in a small space? That's where today's RV water heaters fall down. They have a simple, shall I say crude heat exchanger that is about the depth of the tube with a reverse of direction at the inner end. You can burn your hand on the exhaust. Better would be a design like an RV furnace; that would boost both efficiency and cost and require a blower. This is also a fairly small market segment and likely not worth the development cost when "normal" residential applications need more capacity or have grid tied electricity available.
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bldginsp
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# Posted: 17 Oct 2014 10:31am
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I see plenty of very small electric water heaters installed to serve a sink that's far away from another water heater. You're right Don that a very small gas heater makes little sense when elec is available. Doesn't help off gridders much, but it would be interesting to see how long it would take a genny to heat up water in a 6-10 gallon elec water heater just to take a shower or two. Might be a viable option for occasional use, just cause the water heaters themselves are so cheap.
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bobrok
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# Posted: 17 Oct 2014 12:09pm
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bldginsp & MtnDon, your explanations and assumptions are on target as pertains to my installation. It is a 6 gal. lpg intended for RV use. And I had no inspection since I did the entire plumbing installation well after the cabin was initially built back in '98.
We only use the appliance when we need hot water, once a day in the evening for dishes and showering. It may be an inefficient heater (yes, the exhaust is rather hot) but I've found that after the initial 30 or so minute running cycle I can shut it off and we can easily do two showers. It's actually pretty well insulated so it can hold water on the warm side for quite a few hours after I shut it off as well.
ty for the info.
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MtnDon
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# Posted: 17 Oct 2014 02:19pm
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If you add extra inches of foam around the factory foam it gets even better. That is what I have done... 4 inches extra. Most of the time we leave it on pilot flame and the water is more than hot enough unless we do two back to back showers. (We have the pilot light model, not the direct spark ignition type.)... Note there are also electronic ignition versions that incorporate an electric resistance heating element.
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toofewweekends
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# Posted: 17 Oct 2014 04:37pm
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"...interesting to see how long it would take a genny to heat up water in a 6-10 gallon elec water heater."
We've done a poor man's version of that, using a small stock tank heater stuck in a 5 gallon bucket. If I remember, it took around 30 minutes to get to shower temp, starting with pretty cold water. Runs off a 2k Honda. We're very much weekenders, so not an option for everyone, but the fuel cost is negligible.
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TranquilMan
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# Posted: 2 May 2015 04:40pm
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Quoting: Ontario lakeside We use a ecotemp at our off grid cabin. I have a video of the system for those interested.https://www.youtube.com/watch?v=funUNu9zVLQ&list=UUGuSGWaR9LgZwYVvaE3sXIA
Ontario lakeside
This is a great video! Exactly what I am planning to do except I don't have the elevation you have to deal with. My question is if the Ecco L5 is outside and I want to run the water into a wash house for a shower and into my kitchen sink, would it be a hassle not being able to easily make control adjustments. Or are adjustments infrequent? I love the simplicity of the system. I'll be pulling my water directly from the lake and am off the grid with solar power.
TranquilMan
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razmichael
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# Posted: 2 May 2015 07:09pm
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Hi Tranquilman,
I use a L5 at the cabin with water fed to an outdoor kitchen/sink, inside sink and a shower (the latter is a temporary setup at the moment. The water comes from the lake but currently I lug it up to the cabin and fill a water barrel.
From the barrel -> debris filter ->On demand water pump (12V)-> Y-connector-> then split to a cold water distribution 4 way manifold (just a standard garden type) and the second line runs through the L5 and back to another hot water 4-way distribution manifold. From the two manifolds I run the double lines of pex out to the three locations connected to both hot and cold taps. Obviously with the smaller size pump I don't to really run more than one sink/shower at a time. In addition, if you open up the cold water all the way the pressure remaining may not be enough to kick in the L5 but overall it works really well. No adjustments needed on the L5 - set it for the maximum temperature you need and leave it. In my case I chose to use micro switches in the taps to turn on the pump (no pressure tank, although the built in pressure switch in the pump will turn off the pump if for some reason the switch is stuck on and the taps closed). First attachment is a photo of the pump and plumbing under the outdoor (really on the deck) sink. Zoom in and you may be able to see some of the design. Second attachment is a simplified diagram I did up a while planning. The L5 is mounted on the outside wall so two lines go through the wall - one out and one return. Overall this design allows for four separate plumbing fixtures but obviously could be done for more or less.
Plumbing.JPG
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Watersimple.jpg
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creeky
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# Posted: 3 May 2015 08:21am
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razmichael. i still love your outdoor kitchen. anyway. why the micro switches? wouldn't the pressure switch in the pump be enough?
lot's of folks on this site have used the eco temps. mostly with good results. has anybody used the Marey? It has some nice features (modulating flame!) and gets good reviews at Amazon.
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razmichael
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# Posted: 3 May 2015 09:02am
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Hi Creeky, Main reason I used the switches was to limit the risk of a leak powering on the pump and spilling water everywhere. More to do with my lack of trust in my own plumbing ability! I also like the "control" I have over the system - no way for it to switch on by itself. Personal choice and not really a strong case for it. As the pressure switch is still active when the pump is powered, if you turn the tap on just enough to start the pump the line pressure will shut the pump off. To keep the wiring simple I use a relay for the pump so the wiring to the taps can be long and thin (only very low amperage).
Thanks again for the compliment on the outdoor kitchen - it has worked out great..
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creeky
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# Posted: 3 May 2015 10:54am
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you're welcome raz. your indoor kitchen is sweet also.
Adding to bldginsp's list.
Ignition: > if you have inverter power from your solar system (ie. ac) the 2w idle draw from, by example, the ecotemp L12 is basically nothing. the 100wh draw to power the fan while the shower is running is also relatively small. a ten minute shower draws 15-20 watts, give or take.
what I'm saying is. don't be put off by power vented propane water heaters because of small ac loads. consider it. but it's a low draw/load factor.
the advantage of power venting is the combustion gases move outside the cabin. you may need to consider fresh air replacement? but not breathing combustion air...
this is another reason why I'd like to hear reviews of the Marey. They have fresh air replacement built in. Similar to most vented propane heaters.
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Notes
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# Posted: 3 May 2015 11:17am
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Hi all, my summer project is installing a HTP combo boiler for hot water heat and domestic hot water. It is a 2 pipe sealed combustion unit, with a modulating burner with a low turn down burner when used with an outdoor reset control. Maximum watts 160. I have installed HTP products in commercial applications, pipe fitter by trade, and have very good results with product and and tech support. I will keep you informed once operational. Also on a side note I am testing in my shop 115 volt freezer/ refrigerator for off grid. Added start components and pump down selinoid for low amp starts and eliminated defrost heaters for old fashioned manual defrost. So for numbers look good. Still some room for improvement. Will post data in a few weeks if time permits for more modification.
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Brknarow
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# Posted: 3 May 2015 11:54am - Edited by: Brknarow
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My plan, for now, is to use a 40 gallon electric water heater. I've been experimenting with a 30 amp switch on mine at home. It takes around 30 minutes to heat the tank which will last me, usually, a couple days during the spring and fall, three days during the summer but I have to run it every day during the Winter. I don't have to during the Winter but I'm happier when I do most often.
I intend to use a generator (I have a 6000watt diesel picked out at the moment) that will be able to assist with topping off my batteries and such.
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groingo
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# Posted: 3 May 2015 01:05pm
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Hot water, we don't need no stinkin' hot water, haven't used hot water for over 20 years....and that's the truth.
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TranquilMan
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# Posted: 3 May 2015 05:36pm
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Thanks Razmichael for the description of your outdoor kitchen and comments. I'm keen to get started as soon as I can get my boat in the water to get down to the cabin. I'll post as soon as I get something working.
Tranquil Man
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rockies
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# Posted: 10 May 2015 06:17pm
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If you have available wood, you could use an indoor wood furnace. I plan on using an Empyre Elite 100.
http://profab.org/profabbrochures/file_817977R01_Elite_Brochure_web_.pdf
It's like those outdoor shed style boilers that sit out in an open field about 50 yards away from the cabin, but instead you put this in a small outbuilding. It will make hot water for radiant floor tubing, as well as the shower, sink, washing machine, etc. Since it's indoors you don't have to load it out in the rain or snow, and any excess heat from the fire box is kept out of the cabin in warmer weather.
I think this is a good system that could be combined with solar hot water. The solar is best in the summer when you don't need a fire, and in the winter when solar isn't very efficient, the wood boiler takes over.
Another plus is you can run tubing underground and heat several buildings at once.
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rockies
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# Posted: 10 May 2015 06:25pm
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If you do want to try solar water heaters, this article might help.
http://energy.gov/energysaver/articles/solar-water-heaters
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rockies
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# Posted: 10 May 2015 06:32pm - Edited by: rockies
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A guy that has built several different types of solar water heaters is Gary Reysa, who writes for Mother earth News.
http://www.motherearthnews.com/diy/solar-expert-gary-reysa.aspx
http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm
The first thing he did was try to cut his consumption of resources by half.
http://www.builditsolar.com/References/Half/Half.htm
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paulz
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# Posted: 10 Jul 2015 11:45am
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Excellent info BI and others. Any updates anyone?
I have an indoor shower under construction with a high 1x3 window next to it. Could the L5 be hung inside and used under the open window?
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bldginsp
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# Posted: 10 Jul 2015 03:20pm
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Not supposed to. I don't want to breathe the products of combustion. I'm building a little shower house and I'm going to hang an L7 outside, and run the shower hose in through a window.
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creeky
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# Posted: 10 Jul 2015 03:55pm
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bldginsp. the amount of combustion gas is going to be pretty small.
but, in other posts you've said you were buying the Bosch. For the pilot light and cheap venting. Not so?
I've been using an eccotemp l12. which has the free included exterior vent but uses interior air for 18 months now. it has frozen once, not too bad, and is still working fine.
if put on a switch it wouldn't require any 2 w/h overhead. but does require ac to run. as noted above. for my solar system size tho the overhead/running costs are invisible.
for an exterior L7: just be aware (I'm not sure what your climate is, but I think you have freezing temps ya?) that with the exterior mount you will lose the shoulder months / cold months every year.
for those who are away from their cabins during the week that means draining each time they leave. draining at night if they are using the cabin. Vs an interior mount which would add months to the usage time. no?
something to consider.
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paulz
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# Posted: 10 Jul 2015 04:40pm - Edited by: paulz
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Quoting: bldginsp I'm building a little shower house and I'm going to hang an L7 outside, and run the shower hose in through a window.
Aren't the control knobs on the unit? Are you thinking you will open the window to turn the knobs?
Is the L12 the smallest indoor unit?
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skootamattaschmidty
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# Posted: 10 Jul 2015 06:07pm
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Ours is the eccotemp L10 and is mounted outside. The control knobs are on the unit but we set the temperature for a comfortable shower and use the taps inside. There is no need to adjust the knobs during a shower.
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