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return duct into back of furnaces

PaulPaul Posts: 246Member
i have seen a few warm air furnaces where they didnt come into the left or right side of furnace for return air duct connection,instead they cut a hole in rear of furnace. every manual i have looked at the manufacturer says a big no to this. i am curious if anybody knows why and what it does or doesnt do to the furnace life or operation.


  • addadd Posts: 94Member
    hi-boy /low boy

    there is different types of air furnaces. what is exactly that you are looking for?
  • PaulPaul Posts: 246Member

    hi boy furnaces
  • John MillsJohn Mills Posts: 837Member

    Check the manufacturers instructions. I'd guess  you'd really be hurting on airflow doing it that way since the air would hit the back of the blower housing and be greatly restricted. As short as today's furnaces are (I know, coils are tall) build a box under the furnace and come in the box. 
  • Big EdBig Ed Posts: 1,086Member
    edited December 2011
    Hazard of open blower cabinet ....

    The blower and fuel combustion would be fighting for the same oxygen ...Improper combustion creates CO .

    The open blower cabinet will cause a negative pressure in furnace room countering the pressure drop needed for properly venting combustibles to the outside ...

    The free wheeling blower without the resistance of a return duct will blow less air and increase amp draw.....

    Less air would increase temperature diff across the

    heat exchanger , eventually burning a hole in heat exchanger ...

    Higher amp draw , could blow a fuse , burn up controls , motors and wires ...
    I have enough experience to know , that I dont know it all
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