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?
Best Answer
Gosh - a buck a therm is "expensive gas rates" - if I could get it (I can't and never expect to) it's more like a buck and a half...year round.
So, you're using 1 million to 1.3 million BTUs/day - if you could manage storage swing of 50 degrees F (not unreasonable with radiant floor, a low-temperature emitter) that might be 3250 gallons of water (at a round but not quite accurate 8 lbs/gallon) and perhaps as much as 2/3d's of that might be in the night when it's colder and nights are longer than days.
2000 gallons of storage is not too hard to manage. 267 cubic feet, less than a 6.5 foot cube, or slice it into a more convenient shape.
Adequate solar collectors to provide the daytime heat for the house AND to charge storage with ~700,000 BTUs in your area might be a considerably more difficult proposition - check the SRCC website and other solar resources. Call it 500,000 if you want to round off for "the other part of the house" but I still suspect it's going to be "challenging" or at least quite costly. I guess you'll pick up some direct solar gain from all those windows, at least when the sun is shining and any other collector would work, so perhaps the collectors can work more on heating storage and less on the house.
Overheating the cellar is probably not an issue - just use insulation under the radiant tubing/heat spreaders.