Today I spoke with a plumbing wholesaler and got some pricing. the backflow preventer's that I need by code if I go single wall are watts 009's and he has them in his system at $266 each. I can find them in the US online for $150 each but that's still $300 plus shipping and duty and taxes. The heat exchange tank that is showing up online as the most reasonable stainless single wall tank is the triangle tube smart 30. It's basically a tank in a tank and it's only $1575+tax to get it here... online once again it's $900 plus shipping and tax and duty... This is making me think dual wall once again simply because the system is rigged to force it.
I see that rheem sells tanks with dual wall internal coils and a built in electric element meaning I wouldn't need to buy a separate hotwater tank which I need to do anyways. They however are glass lined steel and have 6 year warranties. which will never achieve payback before failing. They sell a marathon line of tanks which are plastic, "inexpensive" have lifetime warranties and appear to have ports for external heat exchangers but not internal double wall exchangers. I've written them asking if they sell one with an internal heat exchanger. If not why not?
I have found stainless tanks with double wall heat exchangers in them but they are $2000 and up and don't have the electric element I would like If I'm spending serious money. there are other options but it's really looking like what I want doesn't exist without spending huge bucks. two pumps constantly circulating the solar fluid giving me 3 pumps in the system is sadly looking like the most cost effective option and I know it's a huge hit in efficiency.
It's unlikely that I can homebrew a piece that will work for this scenario and pass inspection.
All this because I may get water in my water...
That $200 coil of pex is looking really really nice right now.
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