I put a small on demand in the shop, and it worked fine.. I tried one in the apartment in my store, and it would not keep up.. so if you decide to go that route make sure you get one of adequate size and heating capacity.. The cheap "on demand" heaters from Menards etc dont seem to work very well. I ended up putting a standard electric water heater in.. and about a week later helped install a Rheem 5gpm tankless water heater... Installation was SO SIMPLE.. of course, it was Electric... but still.. hooked up the two water lines, wired it in, and turned it on.. that unit was around 450 dollars, and as i understand it is working very well.
My old house had hot water/baseboard heat, and that also heated the hot water. My new house has an electric hot water heater.. BUT, that hot water heater is fed through a radiator that is heated by my wood stove. So, Hot water goes Into the hot water heater. All it really has to do is keep the water hot..
If wife and I are BOTH in the shower, and run out the water from the hot water heater, i can actually FEEL the water get hotter as the water fed through the radiator hits the pipes. I have climbed out of a nice HOT extended shower on a COLD blustery winter day, and looked out the window to see the ol smoke billowing out of the chimney on the wood shed... just have to be willing to toss more wood in!
