I read info with interest. I live Southwest (4400 ft up) of Calgary, Alberta. 3rd best spot in Canada for solar heat. Very sunny, especially in winter. Very easy to increase water storage if needed. Another 300 gal tank available. I had intended to insulate the tank. I also was going to bury uninsulated lines in the bottom of thr trench as a heat sink if solar panels produce too much in early spring and late fall. The NG boiler is already controlled by adjustable aquastat that turns off power to unit if incoming water is over a preset temp. Because the house is fairly large, 2200 sq. per floor X 2, but is
very tight, well insulated and good windows we were heating with only about 90,000 btu. That did not include domestic water.
I am trying to provide all domestic water and morning heat for early fall, latr spring and summer with solar and only use coal boiler for maybe 4 months in winter. I also was trying to keep system as simple as possible. Also Boiler, tank and lines are either well insulated or buried below frost level. Anti freeze is about $24 gallon and I was only going to use in solar(it's open to elements) with boiler etc in insulated building. I think there will be enough lost heat, even from insulated tanks, lines to maintain temp in 10'X14' building.