Hello, all. I have someone designing a new hydronic heating system for my home, and we are stuck on the thermal storage issue. The designer would like to use pressurized storage; I have a finished basement with cinder-block walls, and getting anything wider than 30" through the door will be very tricky. I need 300 gal capacity (as a minimum) up to 550 gal capacity (ideal). I'm open to outdoor storage, but that would probably require excavating. Plus, winters here bottom out at -40, so we'd have to make extra sure of the insulation. What ideas have people come up with for DIY storage tanks; and where can I find articles about how to make 'em? Also: Is there a commerical option for this that is so good or so popular that people don't bother?