Not a gret idea. * \, A* S! W( w3 ^& e# O! P1 r9 I( r( I$ o+ @2 ^; q# r9 \ I/ o
Hot water has went through all your home's internal pipes whereas cold water comes "direct" from your local reservoir. Which should be pretty safe. 7 m) }6 r* z- v) e5 K5 u! p1 M6 K; }5 v' }+ c- W
Beside,furnace hot water coil is made of metal. Some of it will come into the hot water.