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How to Seal Leaky Ductwork | Ask This Old House

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By Quentin Peters
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Richard Trethewey shows an innovative new way to seal ducts from the inside. (See below for steps.)

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Richard uses a new technology to seal ducts from the inside.

Steps for How to Seal Leaky Ductwork:
1. Remove the grilles from all of the supply and return registers.
2. Plug each duct register with foam rubber and wide strips of tape.
3. Pressurize the duct system with a blower fan.
4. Use a computer to analyze the data to determine the amount of air leaking from the ducts.
5. Use the blower fan to mist the inside of all the dust with liquid-rubber sealant.
6. The sealant will find and plug all air-leaking holes, cracks, and seams.
7. After applying the sealant, run another pressurized blower test to verify the improved results.

Richard demonstrated sealing ducts using the Aeroseal System [https://aeroseal.com/].

Expert assistance with this project was provided by Boucher Energy Systems [https://boucherenergy.com/].

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How to Seal Leaky Ductwork | Ask This Old House
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Quentin Peters

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  2. Most HVAC companies are guys who start their business because they know they can do a replacement and pocket 3 grand. HVAC ductwork isn't a trade anymore.

  11. I'm going to spitball here but in addition to all of this. I was a installer and every house we went to the "sales team" always had us install 4.5/5 ton condensers when the original ones were 2 tons. aprox 1500 sq/f houses.I dont work there anymore but school said never to do that and the company said it was "necessary"

  19. The dust is probably from a stronger blower than the old furnace and stirring up the dust in the duct work. It’s not from leakage in the duct.

    As for cost of this versus saving and paypack, I would be interested in that.

    Plus all leakage isn’t into unconditioned space, so you are not just loosing it, it may not be going to where you want but it’s still in the thermal envelope

  21. Absolutely no heat loss here even if the ducts leak a little in the basement
    This is called stack effect or chimney effect where hot air is constantly rising
    If you experience cold rooms save your money by adjusting the floor registers to push more air into rooms that need more heat
    Everyone is trying to sell their gimmicks to you Not needed in a properly installed HVAC system

  22. If metal is a good conductor of energy, why is it used between the air handler and the room?
    Doesn’t it lose 40-60% of its efficiency?
    Why not pvc?

  24. I've always wondered about something like this. My house was built in the late 60s. Anywhere a branch came off the main duct or return was massive leaks. I cut holes in the supply trunk and return wherever I knew ducts were coming in and out. I then sealed those branches with proper metal duct tape, duct mastic, or a combination of both. I then cut a larger piece of sheet metal to put over the hole, screwed it in and sealed it with more duct mastic. That helped quite a bit. There are still some areas I need to get to that I can't at the moment. Those spaces above other one one suffering the most above the garage.

  42. Prohibitively expensive in NNJ. But this is typical of initial installation being done so poorly. Hvac installers have their sights on the next install job before they even finish the current. Just the way it is with most of these guys. They demand top dollar for poor craftsmanship. I speak from personal experience.

  43. Do HVAC installers do this, or is it a specialized thing? I recently had a new furnace and new air conditioning put into my 1939 house with original forced air ducts, and I'm thinking I should probably get this done. My HVAC installers did not mention anything like this, but they did refer me to a duct cleaning service.

  45. you could just use some HVAC mastic tape or mastic sealant for about $25 from home depot and do it your self….or you can pay a guy like this $1000 or more to seal your system. They need to rename the title…

  47. Cool technology. Better check the fan static pressure before you do this. If the fan is already having to pump against high resistance on leaky duct what do you think the resistance will be once all the leaks are sealed? The key is properly sized and sealed ducts. Old ducts are notorious for being undersized

  51. Ran hundreds of High Bill Complaints for the gas utility in St Louis, Missouri & I can tell you first-hand this service boils down to ductwork in unconditioned areas and ductwork in conditioned areas. For ductwork in unconditioned areas this service can be advantageous.For ductwork in conditioned areas such as basements or inside soffits there is very little advantage and in some cases big disadvantages. I had a customer that actually had a reduction in basement heat ,much like this installation & the water pipes froze one cold winter night ( I believe the Insurance Company for the duct sealing service picked up that bill).

  52. This really should not be much savings unless he has leaky pipes in the attic or elsewhere that is not insulated. If he wants the basement and upstairs bedrooms not to be heated in the winter. The problem is at best heating the wrong areas of the house. The dust problem can be fixed by sealing the basment floor and intalling a hepa filter just before the cold air goes into the furnace. Do have an furnace filter? Probably want to remove it if they do

  56. Looks like a paid advertisement, the actor never called the installer to rectify the problem. Everything was staged to show off the new technology.

  58. How would this affect damper operation?
    What about the AC coil and other equipment like the existing blower motor? Would they not also collect the product on them?

  63. Awesome information. I was wondering if my duct work was in good shape. I got this place this year and the duct work was put in around 1974. I have already done some work to seal the Duct work. After seeing this I know to take a closer look and return and supply duct work. Thank you so much for this video.

  64. It's November 13, 2020 and the coronavirus is rising fast. My husband went into the attic and found a separation in the ductwork. We want to hire someone to seal it but not during coronavirus spike. I threw him a towel that he wrapped around it. Will that help much? 50%?

  70. All of this makes sense but how do you know that material isn't toxic over time when heat is applied or over time it breaks down? Not comfortable not knowing what this material is made of.

  71. Another marketing sales pitch, doesn't last and the cost doesn't save you much on your energy bills. Take their quote and spend that money on better windows, doors, and more insulation for better savings

  79. The cost of getting this done would eat up your money saved on heating your house for probably years before you'd get a return on it. The fact he was complaining about heat is surprising cause the duct is even insulated which we don't do up here where I live and its winter 8 months of the year. I'm guessing probably undersized furnace or ductwork, and as for the dust, if you run your blower on the furnace non stop it creates more air flow in your house making less dust settle and it won't eat up much electricity. Another option is to change your duct work into a 2 zone system so if its different temps on different floors the system will only heat where its needed.

  85. DOESN'T SOMEONE FROM A COUNTY IS SUPPOSED TO OKAY THE NEW AC AND THE AC DUCT SYSTEM???!!! WHO IS RESPONSIBLE FOR SUCH SHAMEFUL INSTALLATIONS OF THE AC DUCTS???!!! SHAME! SHAME! SHAME ON THEM!!!!!!!!!!!!!!!!!

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