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I have a basement that I would like to finish and install a drywall ceiling. And I would like that ceiling to hide the HVAC vents.

However, the vents already just (by an inch or so) go over my head. If I put drywall around them, the ceiling will be short, which is especially a problem for the vents in the center of the room (less so for those by the wall)

Currently the vents hang from the floor joists by 4 inches.

Can I secure the vents directly to the floor joists or have them hang by only an inch? Is this safe to do?

Photo of vents by wall

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    If they contact the joists they will transmit any noise from the vents better. That may not be a problem but it would be easy to put a layer of rubber-like material between vent and joists.
    – blacksmith37
    Apr 21, 2020 at 15:12
  • Thanks for pointing that out! Now if only I knew which answer to mark as correct because technically both are solutions to the actual problem.
    – Merlin -they-them-
    Apr 21, 2020 at 19:23

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You should consider switching to low profile hvac duct. You can get a wider version that is shorter but carries the same air. If you can't find something off the shelf an hvac professional can design/fabricate one that will work. Won't hurt you to get a quote and see what your hvac guy can do for you. Would be a shame to put the effort into finishing a basement and have crazy bulkheads running everywhere.

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  • Thanks! I didn't know about low profile ducts. I'll definitely look into those first. It would add a lot more space
    – Merlin -they-them-
    Apr 21, 2020 at 19:20
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Usually I mount the vents to the joists so I would generally say yes you can move them up. However there may be a reason the ducts were lowered. I also usually box the vents so just that area is low, it matters for resale. If the entire ceiling is two low sometimes the space cannot be listed as living space.

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  • Yeah I was definitely going to box them. But it would still be annoying even for just that area. Do you know what reasons there might be for lowering the ducts?
    – Merlin -they-them-
    Apr 21, 2020 at 13:45
  • I have seen electrical / plumbing runs along the bottom of joists and the duct work was installed directly below those runs so the ducts had to be lowered. With some cases a difference in joists from 2x to TJI caused a different height and the installed kept the duct straight, I have seen a few but most are attached directly to the wood. Maybe someone was going to insulate? I would want as much head room as possible but I am 6’5” and my son is 6’8” so we really notice low points.
    – Ed Beal
    Apr 21, 2020 at 14:01
  • Ah okay. I don't need to run anything between the ducts and the joists. I was mostly concerned about it being a possible fire hazard and/or code issue
    – Merlin -they-them-
    Apr 21, 2020 at 14:20
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    On the jobs that I ran, the HVAC guys really did not want to run the duct work tight to the joists, because of sound transmission. 3/4"-1" was the minimum they would allow to satisfy their concern. On duct work less than 22" wide I had the duct work set away from a wall 2-3" so I could set a ledger beside the duct to the wall so the bottom of the ledger is 1" below the duct, and use 2X2 and plywood to create a structure to carry sheetrock on the outside face. This allowed drywall to pass under the duct work by 1" maximizing the headroom
    – Jack
    Apr 21, 2020 at 16:16
  • It all depends on how the duct work is set up. If there is no flexing in free air the ducts are the right size / pressure there will be heat creak in any case. Where there is a space issue I tie tight to the joists with only a thin insulation blanket and box the bottom and sides the same way , haven’t had problems with combo heating and cooling systems and this provides more head space. As long as there is a minor barrier the thermal creaking is about the same for the systems I have installed.
    – Ed Beal
    Apr 21, 2020 at 18:46
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If your supply ducts are used for heat with a gas furnace, here in Western Canada the code is to leave an inch between the supply ducts and the flammable wood in case the furnace overheats due to a plugged filter or other technical malfunction. Normal operation furnace air can go to 140F, and of course a malfunction can drive it much higher. Fine to have cold return air ducts touching wood or using joist spaces, but can transmit noise as mentioned already.

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