Marshall, (Pensacola, FL)
Marshall, not so much with motorhomes, but LP-fired, tankless water heaters are proving to be a viable alternative on other types of RVs today. Years ago Norcold, (yep, that Norcold), produced an instantaneous water heater call the Vaillant. It was used predominantly in the 1960’s and through the early boom years of the 1970’s. That model died with the advent of direct spark ignition water heaters still popular today.
In today’s market, one accepted design of instantaneous tankless heater is produced by Precision Temp. Their RV-500 model fits into the same space as the current 10-gallon units do now. You can read more about the RV-500 here. You will find them factory equipped on some fifth-wheel trailers and as an option on many other towables. It’s my belief they are not being used so much on motorhomes because of the fact that most coaches have the added benefit of the water heater being plumbed with motor aid; whereby heated water from the engine’s cooling system is routed through the heater so the stored water is hot and ready to use when the motorhome stops for the night.
Though I have not personally tested the RV-500 (coming soon), I’ve studied the product and published reports indicate hot water begins to flow within three seconds of turning on the faucet. Users I have spoken with are quite happy with economics of the tankless model. They reportedly provide about 200 more gallons of hot water for every tankful of LP consumed. And with a lower stack temperature. They weigh about one-fourth of what the typical 10-gallon unit weighs when filled with water which is one reason why you’ll find them predominantly on towables. UPDATE: The RV Doctor Product Review of the RV-500 can be found here!
For winterizing purposes, they only require about one pint of RV anti-freeze. Will they ever become popular on motorhomes? That remains to be seen, but certainly tankless water heaters have found their place in the RVing realm.