Best Propane On-Demand Unit For Solar Pre-Heated Water?

Steamback

As other posts have indicated, not all on-demand units are equal. Some (like Navien) fire the burner and heat water upon flow only. I ran in to this recently when me (solar guy) tried to work with the guy in charge of the propane backup...I'm kicking myself for not checking up on him to make sure the Navien would play nicely with our solar heated water (anywhere from 60F-170F). Needless to say I lost money on the job after modifying the total system with extra control and 3-way valves.

My question to all solar guys is this: What brands/models of propane on-demand units do you like best for playing nicely with solar pre-heated water which can vary from 60F to 170F? What's your short list for on-demand propane units that are reliable and also modulate firing most precisely according to incoming water temperature?

Thanks in advance...

jumper

Instant demand are supposed to be able to turn down. Is the propane in series or in parallel with solar?

hot_rod

I’m not sure any of them would want to see 170 inlet? Motorized or thermostatic shuttle valves are one way to maximize both.
You need temperature control of some sort for that 170 condition of course. Whether it flows through the heater or not.