- u# q% X9 D$ g: @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. 2 M, r8 R* Q. ]: }2 k; T( c0 u% X& U8 ~8 \5 q5 Q* I
Beside,furnace hot water coil is made of metal. Some of it will come into the hot water.