Not a gret idea. + {4 K/ t$ N' D& ?2 |0 a # u( ], [/ K) u' LHot water has went through all your home's internal pipes whereas cold water comes "direct" from your local reservoir. Which should be pretty safe. 0 X+ h8 k7 R) H- ]0 s) s $ r/ {. E2 @1 s9 ^" wBeside,furnace hot water coil is made of metal. Some of it will come into the hot water.