The system will be drain back. Heated by a water loop in the woodstove (wood is currently our only source of heat) and solar panels. DHW preheat will be one load. Space heating will be via old cast iron radiators I found at auction (heavy!). I had intended to build my own collectors but the tank alone has taken me three years and counting. So I asked for recommendation here and Mikesolar pointed me to Thermodynamics Ltd.. I've spoken to them and they seem happy to quote on custom sizes as well as the their standard ~ 4' x 8'. I have to decide where to put them. I have two options. A roof slope eyeballed at ~ 6/12 or a south facing wall. The roof has more area available but it adds ~ 6' of head and the angle is less than ideal. The wall is problematic with window penetrations, soffit overhang, and odd dimensions.
And yes, the PEX is oxy barrier ;-)
