2 A& I& G5 T3 x. c# ~( aHot water has went through all your home's internal pipes whereas cold water comes "direct" from your local reservoir. Which should be pretty safe.6 b% Z( K) g5 p: `, |, M9 t0 c
9 f: A7 k5 u: h( G4 q$ k
Beside,furnace hot water coil is made of metal. Some of it will come into the hot water.