For a tank type water heater I could see that argument, but for a tankless, what really is the difference between that and a propane
stove on a boat? I know some people are opposed, but 10s of thousands of boats operate with propane stoves just fine. And with a stove the combustion products end up in the cabin
, with a tankless water heater they get vented outside.
With a proper solenoid valve installed (as with a stove), no reason that a tankless can't be operated with propane shut off at the tank except when in use. Heck, you could put a flow switch in series with the manual switch, so that the solenoid would only operate when someone turned it on and there was water flow in the shower
. I could see finding a ventilated, separate compartment to install it in being a problem on most boats, but that's a different question.
And, while expensive, this heater is
designed for marine installation