Build your own Water Heater / Furnace Unit?

JD5150 wrote:

adamis wrote:

JD5150 wrote:
I have worked around air to water heat exchangers most of my life. Hot air from engine exhaust blowing on a stainless or copper coil to heat water at 600 psi around 2 gallons or more a minute.

The idea you have most likely will not work. Someone mentioned that a 12 gallon RV water heater is around 12,000 btu. So lets say a 6 gallon one is 6,000 btu. By the time you use air flow/fan to blow the heat you will be down to 3,000 btu or less. The fan will cool the air some so there will be some loss of heat there from fan picking up cooler air and blowing through the radiator coil.

I just started looking at the Truma Combi eco plus. I'm still studying it to see how much juice it will take to run in electric and gas mode. I want to run it off solar and a 200 amp hour lithium battery pack plus gas if needed. It will do both at the same time

The lower BTU output actually works to my advantage in this scenario. An Atwood 8 Gallon water heater is 8,800 BTUs, an Atwood Furnace is 35,000 BTUs. I don't need 35,000 BTUs constantly, there is a cycle time involved or I will be cooked out of the camper. Having a constant 8,800 BTUs burning with a lower fan speed and lower overall heat level but over a longer running time can have the equivalent effect as a blast furnace running for shorter periods of time.

Lower BTU then it should work. Are you going to use a 12 or 110 volt pump to move the water through the heat exchanger? If so you can find pumps that can handle 140 degrees without damage. There are very few that can handle 180 degrees without damage.

The TACO IFC circulator in my shop PEX system will handle up to 210 degree fluid (which can be water or Glycol), no problem but it's 110 volt. However the amp draw is very low (like 60 watts in the high position and 15 watts in the low position. You could run it from a PSW inverter and run on 12 volts, no issue.

I could see circulating hot water from the HWH no problem through a fluid to air HX with a fan behind it, installed in the cavity where the existing furnace is now. Would be a fairly cheap install and add a t'stat to cycle the pump and fan. No mods to the HWH at all, other than a return line to the HWH for cooled water and let the HWH maintain the tank temp. Has some interesting aspects so long as the HWH can keep up with the demand.