My home isn't fitted for gas so, I wanted to know if it was feasible to run a Paloma LP tankless water heater (7.4gpm / 19,000-199,000btu) using a 100 pound propane bottle?
199,000btu would not last very long on a small bottle like that.
You should get a real tank, or use NG.
25 gallons is 2,300,000 btu's. A good ballpark is 100k/hour to heat water for a shower. If take 10 minute showers thats 16,600 btu per shower or 138 showers per tank. Many people have transport issues. Go without a shower for a few years and you might think that tank is real enough.![]()
I have the 3.8 gallon Rinnai >>outdoor<< unit running from a 215 gallon LP tank using a high-pressure system. I have 10psi to the house through 3/4 inch underground plastic gas pipe, and then 1/2 inch black iron inside the cabin and through the wall to the unit. Pressure regulator is at the unit. Absolutely no problems with condensation on the pipe, or of getting enough BTUs to the unit even in the coldest weather. There's no reason you can't use a portable tank.