Greetings! Can anybody suggest an on-demand propane hot water heater that will do all of the following: a) heat all the domestic hot water b) heat via radiant in floor heating c) DOES NOT USE ELECTRICITY d) If c is not possible, uses ideally less than 30 watts/hr when in use. I'm off-grid so I'd like a propane hot water heater that doesn't use electricity or uses very little, and I'd prefer on-demand so the pilot light of a propane hot water tank isn't constantly on, and to save some room instead of having the tank. I'm a new homeowner organizing a new house off grid and have no idea what I'm doing! Wheeee! I have a great builder though. So far everyone has told me the best on-demand we can find uses 60 watts/hr, which is too much. Thank you!

A lot of tank hot water heaters don't have pilot lights anymore.

Units of 30 watts/hr is an acceleration. You're probably looking for just watts(?), which is an energy rate (joules per second). At 30 watts per hour staring from zero, in 10 hours it'll be burning 300 watts.

Hydronic heating systems almost never make sense for off-grid applications. The pumping energy requirements alone are fairly cost-prohibitive when looking at the PV + battery necessary to run it. Using a tankless rather than a dumb cast iron boiler is even worse, since the high pumping head of the heat exchanger in a tankless takes a LOT more power than what it would through an atmospheric drafted cast iron boiler that's fairly tolerant of almost any flow, and has very low pumping head.

Designing a hydronic heating system is way more than a plumbing exercise, and designing one that uses only miniscule amount of electrical power is even harder. A "design by web-forum" approach is not likely to deliver a satisfactory result. As much fun as it is to play "junior hydronic engineer" using tankless water heaters on my own stuff, I wouldn't touch an off-grid radiant floor application, because it's simply NOT where the money is best spent.

Designing the house for minimum load and tweaking the hell out of it with BeOpt simulations comes first, at which point you can get a reasonable handle on the heating load. Right now ya got nuthin', but seem enamored of the concept of radiant floors. Hopefully that's an infaturation you can get over, but if you can't, a tankess water heater is one of the worst possible choices. A propane TANK water heater has lower pumping head, and a cast iron propane boiler even less. But it's still better to spend the money on fine-tuning the insulation and window specifications to get the load down to the "who cares?" range. That's cheaper and more comfortable than a Rube Goldberg heating system design and the PV & battery necessary to run it.

Empire makes several types of propane fired wall furnaces that use no power. When you're closer to knowing your design heat load you might look into them.

I concur with Dana. For an off-grid HR heat source one should be thinking hydro power into an electric boiler (look at the NextGen Boiler if you do this), solar collector and storage tank, or micro co-generation (both heat and electrical power from a generator) and storage tank. The last thing I would do is put PV on my roof if I was in wildfire area. So if you do PV, you might want to consider ground mounting the panels. And if you do PV, you might want to consider mini splits...although complex heat pump systems can be problematic in remote off-grid buildings.

Not every location has reasonable access to micro-hydro options (just sayin'...)

Even where that option exists, air source heat pumps might still be cheaper than the additional amount of generator needed to run an electric boiler. Off grid power is expensive.

Start with minimizing the load before deciding on solution that meets that load. The smaller the load, the simpler, cheaper and more reliable the solutions become.

No, minimizing the load is the second step. The first step is finding property with adequate hydro power potential and/or adequate solar exposure for solar collectors or PV. If you have adequate hydro power you don't need a generator except for backup. The only problem with hydro power is convincing fish and wildlife to let you dump the excess power as heat back into the stream...

Oh, and a wood-burning masonry heater is another great heat source option for an off-grid energy efficient home. It can operate very efficiently and is cleaner burning than any EPA certified stove at the lower heating levels needed in an energy efficient home. One very short burn a day and you can have a fairly steady 24 hours of radiant heat. You can also install an internal water heating coil that is heated by the masonry heater for domestic hot water use.

If you are considering off-grid life, it is always best to engage with people who are actually successfully doing it and benefit from their experience.

The only problem with hydro is finding the suitable hydro resource. That's a lot easier task in the Pacific Northwest than it is in most of Nevada, Arizona, or North Dakota.

The masonry heater makes sense over a wider range of locations than micro-hydro, with a lot less complexity to the design, construction & maintenance too, as compared to creating a private nano-utility grid to be able to run a more complex hydronic heating solution