I have a 3 story house and a furnace on the 1st level for levels 1 and 2 and another in the attic for the 3rd level. The furnace is in a closet with vented doors and the 1st level is always cold in the winter. I think that this is due to the vent pipe(which is just a pipe running from the roof to the 1st floor furnace room) which stops at the very top of the ceiling in the furnace room. The pipe is always cracking an popping loudly inside the walls and is leeting a lot of heat out in the 1st floor. HOW CAN I STOP THE CRACKING SOUND AND KEEP MY HOUSE WARMER? HELP!