Not a gret idea.: K% @. [! |$ t5 v& N
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Hot water has went through all your home's internal pipes whereas cold water comes "direct" from your local reservoir. Which should be pretty safe. , O3 ^+ y9 S4 C* b' g% T1 g/ L1 Q8 M9 |1 r
Beside,furnace hot water coil is made of metal. Some of it will come into the hot water.