I've been preheating water with a couple hundred feet of black garden hose on the inlet to my LP water heater in the summer. I'd like to have something a little better. Was looking at the evacuated tube heat exchangers but figured with my hard water they wouldn't last(hand dug well, brick lined). I don't really have room for a heat exchanger tank where it wouldn't freeze like you might use with a closed loop & glycol & those systems seems relatively expensive. I was thinking maybe the flat plate collectors like they use for swimming pools might be a good option however they don't seem to be rated for much pressure at high temp. It looks like that I'll just use what ever I come up with during summer so don't want to invest a lot & I'll have to drain it in the fall. Do you think the flat plate collector would hold up assuming the water pressure never exceeds say 50 psi? How suseptible to scaling & lime build up are they? Any that are easily cleaned? Maybe I'd be better off building my own collectors but I was worried about logevity & expense. I'd think wooden frames might not last with the temp extremes. Anyway, what are your thought? What are you using if anything. thanks.