I have two furnaces in my house, one for the basement and one for the rest of the house. I noticed that while using the basement furnace this winter that no air was coming out of any of the basement vents (all under cement/under padded carpeting) except the one closest to the furnace in a bathroom. And it was blowing what looks like dirt out. I have had two HVAC professionals come for other things, routine maintenance and have asked them what would be a good solution. One guy said to ditch the system and invest in a Mitsubishi splits system. The other simply had no idea if it could be repaired (easily/inexpensively).

I don't really need the bottom furnace since the other furnace actually does have some output vents in the ceiling in 3 places. But the basement is always about 3 to 5 degrees colder than the rest of the house, so the second furnace would be nice to have. I mean, the furnace works and everything, it just can't circulate because all of the vents are collapsed. Also, it's not very comforting having a broken HVAC system lying around.

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    How finished is the basement? If it's just a couple large rooms, how about running new ductwork along a wall or ceiling and box it in with drywall? Should be cheaper than breaking open the concrete.
    – Johnny
    Mar 6, 2015 at 23:10
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    It is completely finished, right now there is a guest room, a bathroom, a game room, a workout room and a laundry room, about 1300 sq ft total and all carpeted or tiled and painted. Running new ducts is an idea,I will have to see if that or doing a good insulating job is cheaper. Thanks :) Mar 7, 2015 at 15:02

2 Answers 2


If your basement is already mostly comfortable without the problematic supplemental furnace and its ducts, why not spend the money on properly insulating the basement instead? That way it will likely be all the way comfortable when heated from the heat of the main furnace, and then you can fully abandon and/or remove the redundant furnace and have lower bills too.

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    +1, insulate the basement and re-balance the main system.
    – Mazura
    Mar 7, 2015 at 1:31
  • Hadn't thought of improving insulation, which is actually a really good idea. A non functioning piece of home infrastructure has really kicked in my ocd this time. Mar 7, 2015 at 15:04

Abandon the below grade ductwork, they're always nothing but problems. Your equipment works fine? then don't get up-sold on a new one. Unless...

If it's a down-flow furnace, you might not be able to convert it to up-flow, to send it through new ceiling ducts, so maybe that's where the one HVAC guy is coming from (why you'd need a new system).

Having to replace the unit and add ductwork will not be cheap, as the other one notes. I also have no input on how to rectify (with confidence it won't happen again) the below grade, failing, concrete-encased, fiberglass ductwork. Sounds like a mold party anyway. Something caused the fiber duct to fail, my money's on water.

If it is, or could be converted to up-flow, just have it dump heat with some registers directly attached to the plenum chamber, or a few pieces of duct, or go as far with it as you want. -I'd pour concrete in the old vents to seal them off.

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    Yeah, it's a downflow. Looks like time to abandon it and focus on the main system. Mar 7, 2015 at 15:06

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