Not a gret idea. 6 i1 t0 B8 H# _- L0 m8 x$ v $ N. m: |" d6 }1 L1 PHot water has went through all your home's internal pipes whereas cold water comes "direct" from your local reservoir. Which should be pretty safe. ' E* r' {! N6 `8 H: k# X % ]$ w: t0 n; ~8 Q' r2 kBeside,furnace hot water coil is made of metal. Some of it will come into the hot water.