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Small Cabin Forum / Off-Grid Living / Propane Tankless water heater conversion to heat?
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# Posted: 5 Aug 2021 15:03

Had this idea.

Buy an efficient, outdoor, propane tankless water heater and hook it up to a circulation pump and thermostat. Install it outdoor and run pipes inside the cabin and hook up to radiators. Since I am in upstate NY - I will fill up the pipes with the special hydronic heat anti freeze so I never have to mess with it.

My cabin is currently 144 sqft (12x12) with 13ft ceiling. I intend on increasing its size by another 20ft... and have a 32x12 (with ceilings that are 9ft)

What I am trying to figure out... is how much propane this will eat. Assuming that during the day we will use firewood in the stove and the cabin will probably not really need this tankless to kick in until 1-2am (when the stove will probably die down) - it really only needs to heat for 4-6 hours at night. We won't spend more than 4-6 nights a month there.

I currently have 2x 40lbs propane tanks there. Any guess to how quickly it will finish a 40lbs tank?

# Posted: 5 Aug 2021 16:02 - Edited by: gcrank1

You would be better off with a ventless lp 30,000btu infrared (Not the 'blue flame') wall heater With a thermostat AND get an O2 alarm. The heater will only come on late when the interior temp drops below 'x deg' and hold the temp until you get up. The alarm is a safety measure. Fwiw, ours has Never gone off unless we test it.

# Posted: 5 Aug 2021 17:24

They have bad reviews.... What was your experience?

How much propane it uses?

# Posted: 5 Aug 2021 21:07

Our experience is great. Our place is one story, cath ceiling, 16x24ish.
We also have a 10k btu blue flame. The BF heats the air that then heats the stuff in the room, somewhat inefficient that. The infrared heats the stuff in the room and feels like a wood stove.
Are the 'bad reviews' by folks afraid of the non-vented aspect? It is controversial but with some ventilation and an 02 alarm and, in your case, limited running, it minimizes your exposure. For some perspective, why havent people been dying all over the country for decades from roasting the T-Day turkey in an lp oven for hours on end with all the top burners making the other food in a closed up house in late Nov.?
If you dont like the idea of non-vented get a vented unit.
The lp use when constantly running is easy math, 1 gal lp is something like 92k btu's divided by 30k btu's running full on is 3+ hours. At less than full blast 30k, say at 15k, its is 6 hours. If cycling off/on with a stat even better.
1 gal lp is like 4.24 lb's so a 20# cylinder is 4.7ish gal.

# Posted: 6 Aug 2021 09:05

Wow that is a lot of propane... Thank you so much for the details.

Have you considered pellet stove?

I have a ductless ac with heat pump. So it runs on gasoline really... Last fall we used it but we don't go tot he cabin in winter yet so this is just future plans.

# Posted: 6 Aug 2021 10:01 - Edited by: gcrank1

Actual, if you are just maintaining a temp in a 'pre-heated' (like yours) and decently insulated cabin/cottage, it would not run All The Time so that wouldnt use 'a lot' of lp (say a 50% run time for your '6hrs' would be, at todays lp price here of $3.29 gal. your cost per night run). Set the stat for 50deg and yours would be pretty economical.
If we go to the cabin in winter and it is 30def F the 30K has to warm up a dead-cold structure and contents, that Will Run All The Time to get us to 75ish deg comfort. Yeah, that costs us more, but any kind of heat costs. That is why I recommended the 30k unit. Ours has 3 levels of setting (7k, 14k, 30k and no stat) You can use it at your current cubic footage and still be good when you expand. Fwiw, ours cost about $200 last Christmas, the stat units were about $50? more, and the separate, portable 02 alarm was $25ish). Vented lp furnaces cost more and are certainly a good choice for many people.
We had a wood stove up into the 1st of this year and and 30+ years of wood stove experience, and we initially would get the wood stove going and WAIT for it to warm the place up. Then we got the first 18k btu Blue Fame lp unit to augment, which really helped, and that led to getting the 30k btu Infrared unit. After that we no longer bothered with the wood stove. I removed it this past spring. I should mention, we did Not have a class A chimney which was going to cost at least $600, but to run your suggestion:
A class A chimney, a pellet stove, pellets, power to run if an auto-feed or requires a draft fan (we are totally off-grid with a small solar-elec) means a HUGE expense that, for us, is better spent on lp gas. In fact, after our experience last year our lp costs were so low that it wouldnt have been any cheaper buying pellets if we had all else in place.
And the gas furnace is on and kicking out 30k btu's within minutes of arriving. That was a BIG win.
We already had lp for the cook stove and some prep for a water heater.
Then there is the insurance thing. Our company wont insure with a wood fired stove even if everything is done perfectly to code/regs.
My quick numbers run last year indicated that amortized out we Might hit the dollars spent tipping point in 10 years, though that wouldnt change the 'wont insure part'. After last winter's experience Im thinking it might be 20yrs or maybe never. We wont likely live that long.
And the install was SO EASY.

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