Not a gret idea.3 e' N+ h) g! J* {! Y- B7 T6 H
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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. 9 }( S- X! }) x: M( J. |+ u3 B$ m# k% ~3 t# T
Beside,furnace hot water coil is made of metal. Some of it will come into the hot water.