Propane heater for radiant floor

[Elmix]

I am looking for inexpensive battery powered propane heater for my radiant floor system. I am planning to have a pex solar heater on the roof so would like to have the propane one just in case the temp. would drops below let’s say a hundred degrees. I was thinking about Marey 5L model but just received a message from their tech support saying that the incoming water should be cold, otherwise it would damage the rubber diaphragm on the inlet valve. 100F is definitely not cold. So I am looking for new recommendations.

 

[UnicornWizard]

I was considering something similar. Any progress?

 

[Elmix]

No, working on electrical stuff right now.