I removed an old coal furnace from my basement. The furnace did not have any duct work to speak of. There was an exhaust pipe which fed into the chimney and a duct that went into the next room, but for the most part all the heat went up through a 30" x 30" hole in the ceiling above it. The hole is covered by a floor grate without any filter or louvers.

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My house is 1100 sqft and reasonably well insulated. Can I install a new gas furnace to use this same hole? Is there a particular type of furnace that would work best for this application? Do I need to worry about a cold air return? I'm assuming I would need to add some kind of filter. I would greatly appreciate any general advice on how to approach this project. Thanks in advance.

  • what are you doing for heat now? was it only the coal in-place?
    – dandavis
    Feb 6, 2018 at 9:01
  • I have a gas fireplace insert which keeps half of the rooms warm. I'm considering just living with the situation as it is.
    – laertiades
    Feb 6, 2018 at 12:54
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    I would consider a mini split heat pump, although gas is cheaper to run. a split system requires no ducts and they heat in the winter and cool in the summer. A main compressor outside powers the system and copper tubing is run to each room that you want heated or cooled. Rooms not in use can be turned off. Power would need to be run to each location and a condensate drain to the outside some states have energy credits for installing this kind of system they are much more efficient than electric heat. A small home can get by with 2 zones for basic heating and cooling more zones even temps.
    – Ed Beal
    Feb 6, 2018 at 14:11
  • Thank you for this suggestion @EdBeal. I will look into it.
    – laertiades
    Feb 6, 2018 at 14:20
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    Just one safety factor to consider. You can not pul the return air and the combustion air from the same place or you risk pumping carbon monoxide through your house and in extreme cases actually suck the flames out the furnace. A 2 pipe direct vent furnace would solve this problem by taking combustion air from outside.
    – user76730
    Feb 15, 2018 at 8:20

2 Answers 2


The question being "can you?", my answer is "yes, you can". There's no reason a gas furnace can't be run with a single air outlet. In fact, it's common for folks in my area to repurpose older furnaces as garage/workshop heaters, often with nothing but the upper plenum or perhaps a single duct run to a convenient location. Return air is simply scavenged from near the floor.

  • Thank you. If you don't mind, let me run a quick idea by you: The furnace hole is near the center of the main floor. What if I installed 4 grates in the corners of the main floor leading back to the basement. The idea being, hot air would come up in the middle, then travel out to the corners of the house, and then back down to the basement, creating a circulation system that would cover the entire house, even the basement a little.
    – laertiades
    Feb 7, 2018 at 1:05
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    Seems reasonable. You could consider running flexible ducts from those grates to the return port on the furnace for dramatically improved flow.
    – isherwood
    Feb 7, 2018 at 3:03

My grand mother had this exact same type heating system in her old farm house. You roasted in the room above the furnace and froze in the others. I would install a better system than the one installed now.

  • Thanks. Do you think it is possible that a different type of furnace would help? Like maybe one with a multi stage valve?
    – laertiades
    Feb 6, 2018 at 12:55

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