I have an old chicken coop that is solid except for the roof. I am planing to build a 400 sf panel on roof and barn wall inside coop I plan on building a 770 gal tank. It is the perfect place for a drain-back with tank right under the panels. I would in-close and insulate the coop and turn it into a greenhouse. The tank water would then be pumped 100 feet to the house for dhw and radiant. Any reason that i should not use drain-back? I think 3/4 pex in collector running vertical up roof and onto wall 12 inch spacing. Any deas on insulated pex? It would be 50 feet through unheated barn and 50 feet through unheated celler. I think I will use side arms to a pair of 80 gallon electric tanks. one is for dhw and the ther conected to wood boiler radiant loop. All suggestions and comments are welcome. thanks in advance.