Not a gret idea.3 [- u" E& V+ W' N% `
! ^2 W% r$ o4 H% S: f' f2 V
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.2 p+ W5 K* v+ ~" \2 _! c
% G; e* y/ g2 y! V
Beside,furnace hot water coil is made of metal. Some of it will come into the hot water.