Not a gret idea. ) a v3 L( J0 q! Z# d g : q: e0 D! `' C4 g3 }" VHot water has went through all your home's internal pipes whereas cold water comes "direct" from your local reservoir. Which should be pretty safe. / ]& u' O" w% R' u # Q! M a) s( a( [: BBeside,furnace hot water coil is made of metal. Some of it will come into the hot water.