Not a gret idea. & u; {/ x4 |+ B 0 @5 h8 f' x' k4 X, {5 Q% EHot water has went through all your home's internal pipes whereas cold water comes "direct" from your local reservoir. Which should be pretty safe. ( [& P; O* f7 G2 S2 d5 U8 i ' t4 ^: @9 J7 X/ M7 @$ D5 ]2 dBeside,furnace hot water coil is made of metal. Some of it will come into the hot water.