I have installed heat pumps in North Carolina. I'm New York now and someone wants to put in 2 tanks.  One 12,000 gallon tank in basement and another 14,000 gallon tank outside. The house is large, 3 stories about 6,000 sqft.  There is a 3 story solarium that will heat the water in the tanks to make heat available to heat the house.  There will be solar on the roof.
How do I start.
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With a comprehensive heat loss calculation. You need to know how much heat it will take to keep your house warm.

12,000 gallons of water will provide 1,000,000 btus for every 10° temperature drop.

If you can gain enough heat from the solar, this might work.