~78% of the energy from the fuel is lost as heat. It takes 8.34 BTU to heat one gallon 1 degree. Start @ 40 f, end at 130 f, ~750 BTU per gallon for domestic hot water.
750 x 50 = 37,500 BTU
Hmm, could you heat your house water on the way home from work, if you had good enough heat exchangers?
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2007 Dodge Ram 3500 SRW 4x4 with 6MT
2003 TDI Beetle
2002 TDI Beetle
currently parked - 1996 Dodge 2500 Cummins Turbodiesel
Custom cab, auto, 3.55 gears