I'm considering a passive solar radiant heating installation in the Chicago area and was wondering if it would be feasible to store enough water/energy to support heating for most of the night. The house already has a gas central furnace, and can serve as backup, but the winter bills have been as high as $300-400 (for about 300 to 400 therms) during last year's expensive gas rates.
Roughly how much water might be needed to keep ~2000 sqft heated when it's 0 outside overnight in a below average insulated house? Orders of magnitude would be good enough of an estimate. I'm really just looking to understand if this is feasible. If this would require a basement swimming pool, obviously it's not.
Also, since the PEX would be installed on the unfinished basement ceiling, I'm a bit concerned about the basement heating up too much. I assume there are ways to shield the basement from the radiant heat via some form of heat reflectors under the PEX?