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If I burn 2 gallon of gas a day and say I capture and store 1/3 of the energy as waste heat that would be about 80,000 btus. (little less the a gallon of propane). Wax latent heat of fusion is 90-95 btu/lb, melts around 130F. Normal heat capacity is 0.6 btu/lbs.
So useful heat for the house starts starts at 70 degrees and heat it to 200, 130 degrees change. 78 btus stored plus the 95 to melt it, 173 btus per lb stored. To store that 80,000 btus of waste heat would take 462 lbs of wax.
Wax weighs 7.75 lbs per gallon, so would need 60 gallons + the tank to hold the coolant to circulate around it.
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