I have not heard great things about RV tankless units. Problems include that the water pressure is not as precise as at home, and you can not always open the fauscet more to prevent overheating or might be camping in a campground with a 45F supply that can only be heated by 50F at 1 GPM, not considering that a warm shower in my case.
By the way to heat 1 GPM at 65F increase, it would take about 45,000 - 55,000 Btu's per hour burner. Some RV tankless units are not this powerful.
So if you do find a unit that you might want to buy, check the burner maximum input. Ask how well they work while showering from the RV water pump. If the gas valve is variable, and has at least three temperature sensors to measure the input water temp, mid tank temp and output temp to calculate how much to open the gas valve for the correct output temp. Many of the higher cost home units have three temperature sensors, and will be accurate within 5F of the setpoint. But this is while on a fixed input water pressure. And you have almost "unlimited" volume of water at home to adjust the water flow to meet your needs, by slowing or speeding up the hot water flow and being able to mix in cold water if you needed to.
A RV does not have any of those things. You can have variable flow and pressure, and adding cold water to the shower can reduce hot water flow through the hot water heater, and if it goes below a certain GPM you might not have enough flow to keep the burner on, or it can overheat if the flow is low and the burner is on. Either will trip off the burner for a few seconds. What happens? Very cold shower.
That said, I do have a tankless water heater. I used it to warm my very cold ground water to about 80F then fill my 100 gallon fresh water tank. Then with 80F fresh water tank, I could take very long showers with the 6 gallon tank.
The tankless heater that I have is a L5, very simple, no temp sensors at all (except high temp limit switch). It has a variable gas valve, just turn the dial manually. It is only $139 and has a 39,000 BTU input.
The L10 is a little more expensive, and has a 55,000 Btu input. Both can be found at Amazon.com
If you need more capacity, my suggestion is to increase the tank heater size to 10 gallons. It will take some wood working, or cabinet adjustments to increase the size. But it can be worth it. And most tankless water heaters fit into the space of a 10 gallon unit.
The 10 gallon unit has a larger burner, about 10,000 Btu's while a 6 gallon typically is only 8,800 Btus'
Your home 40 gallon water heater is typically 40,000 Btu's and will heat about 40 gallons per hour. So the 6 gallon will heat up in about 45 minutes, while the 10 gallon will put out about 10 gallons per hour.
Fred.
