Re: Tankless Water Heater, CNG?
Now I don't want to be spreading miss information, but I contacted Precision Temp about the ShowerMate M-550. I specifically asked if it was ABYC approved and they said yes it is. He did not provide any documentation at all though. I do know they are not legal at all in Canada on boats.
Another option would be a hydronic heater and they offer a heat loop for the hot water but they run on diesel. It is kind of pricey.