I have a furnace with AC in the basement. I have poor airflow in my top floor vents (furthest from the furnace). and even the room with the cold air return doesn't change temperature very quickly. Meanwhile, the basement and main floor do heat and cool much faster, leading me to believe that my ductwork is leaky. I've examined the ducts, some of which are exposed in the unfinished basement, and many of them have small gaps and holes. Much of the ductwork runs entirely sealed in the walls.

I've heard of Aeroseal, which can seal the gaps throughout the entire system. The process seems simple enough and thorough. Is there anything similar I can do myself to achieve a similar result?

  • what is Aeroseal?
    – jsotola
    Jul 24, 2023 at 6:10
  • I dont see how a seal is going to help. Maybe more information is needed Jul 24, 2023 at 7:20
  • 1
    Please note that Aeroseal can only seal small cracks and holes, I would first make sure larger gaps and holes are mechanically sealed. Pay particular attention to junctions, takeoffs, etc. and seal them with mastic.
    – Glen Yates
    Jul 24, 2023 at 13:56
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    Interesting that you've jumped straight to "leaky duct work" as the culprit. One room in our upstairs has had poor heating and cooling for a number of years - there was a very long 6" flex duct installed to bring air to that room. It had a large number of bends and had actually been pinched off by the strap used to hang it in the crawl space. Even after replacing it with a shorter, non-collapsed run, we still had poor airflow there. A duct booster fan (installed in conjunction with other vents for an addition) has remedied the problem. Make sure you're chasing the right problem.
    – FreeMan
    Jul 24, 2023 at 16:53
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    Have you attempted to balance the system by adjusting the louvers on lower-level vents? That's step one in my book. I've never even considered trying to seal ducts retroactively and without access. That sounds like the modern equivalent of automotive undercoatings. Horse hockey, in other words. If you can't seal them with tape and silicone you can't seal them reliably, period.
    – isherwood
    Jul 24, 2023 at 19:53

2 Answers 2


Air ducts come in 3 type instals.

Under the roof, in the crawl space under the home, or totally hidden in the walls and ceiling.

Aeroseal is a promising product and it works well but has limitation. There is not much difference to similar products.

If the gaps are smaller than 1/8 of inch it could seal them. If they are bigger it wont work, then the manual method of sealing the ducts has to be used.

Most modern heat exchanger blowers have 3 speeds. Most installer just set it at medium speed (at about 500 CFM).

Check yours and change it to high speed to get more airflow.

Meanwhile check the ducting under the roof, and seal it with ducting tape.



if it is this "Aeroseal", where they claim at 2:20 in that a 3-ton AC is a common size and a typical duct system commonly leaks 30% 40% 50% of air which is leaking an entire ton of AC or more... surprised they didn't just ramble 70,80,90 percent, if you want to believe this bamboozle sales pitch then go for it. The only worthwhile part of this pitch was the old spice commercial that interrupted it. Another red flag, at 5:20, "the technicians actually do look like scientists because they have their laptop." which is an emotional play on ignorance.

you would measure CFM air flow out each vent to properly ascertain if the duct and/blower is pushing the proper amount of air. Duct work isn't built inherently leaky, believing that is plain ignorant.

Is there anything similar I can do myself to achieve a similar result?

  • use $5 foil tape and seal ducts you can reach and identify that actually is leaking
  • buy a endoscope off amazon with a long wire and look within your ducts for obvious faults
  • adjust your dampers
  • change your filter
  • inspect the blower fan for correct operation
  • inspect / clean the AC coil
  • ductwork is not meant to be pressurized and hold pressure, that is a false assumption. It's purpose is to be adequately sized and routed to allow adequate flow with little to no backpressure. Their claim at 7:40 of a really tight duct today is 20% leakage is wrong.
  • tape off all vents but one, remove air filter, measure CFM with an inexpensive anemometer, do for all vents, check with air filter installed, adjust blower speed and dampers. It could be as simple as you just need to run a higher blower speed given your duct work sizing, lengths, and bends. There are air flow hoods that will give a more accurate cfm measurement but aren't cheap.
  • Thank you! The ductwork appears to be rigid, but an endoscope and anemometer are a good place to start. I'm simply following the line of logic that my main floor freezes while the upstairs is warm. I'll look into these recommendations!
    – Camron B
    Jul 26, 2023 at 4:34

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