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Duct furnace needed

zepfan Member Posts: 375
Does anyone know of a company that make a gas fired duct furnace between 125- 150 mbh input, that is now more wide then 21"? We need to replace a modine duct furnace that was installed in the building before the roof was installed. Now the heat exchanger is cracked, and the heater needs to be replaced. The only way to get the new heater in the attic is through the access hole which 41"x21"
Thanks to all


  • rick in Alaska
    rick in Alaska Member Posts: 1,420
    You might have to get one and take it apart to make smaller pieces that will fit. Can yo just get a new heat exchanger?
  • Henry
    Henry Member Posts: 996
    Modine replacement duct furnaces are only certified with no ducts after the furnace. You need to get a complete unit with the fan unit. I don't understand why you have no access to it as it should be below the roof if it is a duct furnace. If it is a rooftop, that is something else.
  • zepfan
    zepfan Member Posts: 375
    Thanks to all. That is what we are going to have to do get the new unit, and take it apart. The way these units are there is duct on the inlet of the duct furnace, and ductwork on the outlet of the furnace. I have never seen a duct furnace, regardless of the manufacturer that does not have ductwork attached to the outlet. Otherwise why would you install an inline duct furnace in the first place? For an application that has no ductwork, I would assume you would use a unit heater. It is below the roof, in my original post I stated that the furnaces were placed in the building before the roof was put on the building. The access that is in the building to get to the units is not large enough to get the unit out as a whole.
    EBEBRATT-Ed Member Posts: 13,460
    All duct furnaces I have seen have ductwork in and out. Otherwise it's not a duct furnace

    depending on it's age and condition just replace the heat exchanger as @rick in Alaska mentioned if it will fit through the opening.

    Reznor and Sterling also make duct furnaces

    Make sure you have enough air flow across the hx and that the wiring is such that the gas valve cannot be energized unless the blower is running and in addition install an air flow switch