Air Duct Sealing DIY | How To Air Seal Ductwork

Duct Sealing DIY – Air Seal Ductwork

Duct sealing will save you lots of money and improve your indoor air quality. Watch this video to learn more:

Air Duct Sealing Video Transcript:

Duct Sealing by Michael Church here and in this video we’re going to show you how and why it’s very important to air seal the run of the ductwork. You all have duct work either in your attic or crawlspace or something like that. Possibly in an unfinished basement. Well if they’re not properly sealed, they are stealing money from you. So you need to make sure you watch this video. It’s a bit of a difficult project. It is probably an intermediate project as far as level goes, so you know you wanna take a look at the video. If you’re gonna will be working in a hot attic and you got 15 runs in the attic, so obviously it can take a while. Take a look at this and then if you decide you wanna do yourself, have at it. But if not call a professional to help you out and I hope you like the video. Stay tuned!

Picture of free crawl space ninja assessment

Picture of poorly sealed and insulated ductwork duct sealingThis is a great example of what we come across a lot in basements, attics and crawl spaces. This is a typical HVAC air duct line as you can see the trunk has been pretty well insulated and the run is actually a flex line with a metal collar and they insulated up to the trunk line. The problem is the metal collar has tabs that allows air to escape where it meets the trunk lines, so when they installed it they did not do any type of air sealing.

So that collar where the main trunk and the run meets his leaking a ton of air. And in this picture it shows you that the insulation is exposed because the adhesive tape that they used has become to come away. And the reason why is because it’s a hot attic and of course wear and tear from the heat makes it pull away from the insulation. Ok I want to take just a minute and show you this part right here. You wanna make sure you get the insulation cut out away from this tab so that you can take the mastic and put on that tab securely. Before I move on I thought it’d be a good idea to tell you why you even want to go through the trouble and the hassle and the possible expense insulating and air sealing your duct system.

Why Air Seal Ducts?Picture of properly insulated and air sealed ductwork duct sealing

According to “a duct system that is well-designed and properly sealed can make your home more comfortable, energy efficient, and safer. They basically listed five different areas that you’re gonna see benefits from when you air seal your ducts.”

Number one is comfort. Sealing and insulating the ducts will help in common comfort problems such as: rooms that are too hot in the summer and too cold in the winter for example. Indoor air quality: fumes from household and garden chemicals, insulation particles, dust. Different things like that get in the duct system. Insulation fibers is huge in the basement or crawlspace where you got these exposed ducts and if you’ve got a dirty nasty crawlspace your sucking in the mold and mildew and whatever is down there. These can aggravate asthma and allergy problems. So stealing those ducts can help improve indoor air quality and reduce the risk of pollutants that enter the ducts and then circulate throughout your home.

Number three is safety: if you’ve got gas water heater or a gas furnace. A leaky duct can produce what’s called a “backdraft” where these gases are drawn back into the living space rather than expels to the outdoors like they’re supposed to be. So sealing these leaks can minimize that risk as well. Saving money.

Ductwork Insulation

Duct sealing is extremely important for comfort and air quality. As you notice that’s the fourth reason. Comfort is the first. Indoor air quality is the second. Safety is the 3rd. Saving money is the fourth. Most of our Picture of rusted ductwork duct sealingcustomers don’t seal ducts just to save money. They have an indoor air quality problem or comfort problem that they want to correct, but in doing that, you’re going to save money. The Department of Energy says that you lose 20 to 30%, did you hear that? Twenty to thirty percent of the air that you make in that heating and cooling process inside the HVAC system is lost inside a leaky duct.

Think about it this way, let’s be conservative and say 25 percent, let’s split the difference. For every dollar you spend, every dollar you spend on heating and cooling your home which is 50% in most cases of your energy bill, is to heat and cool your home. Every dollar you spend, twenty five cents of that dollar is lost in a leaky duct system. So this could save you a lot of money over time.

Then the fifth reason would be to protect the environment. Obviously the less energy we use, the less we have a problem with the environment, and the less fossil fuels we use or whatever. And those are the five reasons why that recommends and shows the benefits of duct sealing.

Air Sealing

Ok hopefully that information on duct sealing I shared with you is useful. Let’s get back to the project at hand. This is the foil tape with the mastic on it that we like to use. This is a great tape, it’s pretty thick, it’s a little expensive, it’s probably 25 or $30 or roll or more. I’ve seen as high as $70. So you can see how I applied that first piece to the collar and also to the main trunk line and the foil tape if you notice has a white backing on it so you have to take that white part off in order to expose the mastic.

Now what you gonna do, there is a mastic exposed and you would take that and put it on just like I’ve done in those two areas in sections like that. It’s easier to work with if you cut in small sections and then you can adjust it as you go around. Now you can see on this part I have already taken care of all the way around in small sections. Just cut little small slivers of the mastic tape. You can also use regular mastic adhesive or what they called duct butter, but with these collars where they have large gaps, the mastic tape seems to work a little better in those situations. Then what you can do is you can roll out a longer piece of mastic and then seal where those smaller pieces come together with the duct.

Duct Sealing Trunk

Here we have an air duct where the two main trunk lines come together as you see they used sheet metal screws to tie these two together and then picture of Ductwork with mastic on joints duct sealingused to duct tape to join the joints here. Very thin duct tape. They need duct sealing. So what I wanna do is cut away the insulation as you can see, just to make sure we do it right, we’re gonna go ahead and insulate or air seal this joint, and then every joint we find you can figure depending on the run, probably every six feet.

So you can see there is where we finished the run and the connector that was there, we used mastic tape on it, and now we’re gonna do the seam just down the run from it a little bit. I think you’re better off using 1 whole piece if you can. You can see I got one long piece to wrap all the way around the duct, so now we are gonna take the backing off and connect it to the trunk. Once you get it stick on there it’s a good idea to take your hand and kind of press it down.

Now I don’t know if you’ve noticed, but I did not take it off. I didn’t take the duct tape off that was on there because that tape is a hard tape to get off if it’s been on there awhile, so you go ahead and rub it and seal it real good with some mastic. It will on there real real well. That’s a way you can do the seam. Get up a little further. Now you see that seams been done and also that run has been done. Okay so this is with the insulation put back together.

Please keep in mind that I cut the insulation pretty wide. So that you all can see what exactly I was doing, but the neater you keep the insulation cut. The sharper your knife, the easier this is to put back together. Also the thicker the tape, this is a little bit thin two-sided foil tape or 2 piece foil tape as you can see the brown down there that’s the backing. Sticks a little better. You can also get different kinds of foil tapes out there. This is not a mastic tape this is actually a foil tape that we use on the insulation itself, so here’s the joint we brought it all back together. You can see all that I had to cut out just to give you an idea So I could show you for the camera, but you have to cut that much of the insulation.

So hope this helps you out and if you like this video, please like this video down below. My name is Michael Church in an attic sweatin’ to death so we can make the house more energy-efficient! Have a great day!

Air Duct Cleaning – Keep Ducts Cleaner LongerPicture of AirSafe 2000 Frame and Filter

Improve your air quality with the World’s Greatest Furnace Air Filter, the AirSafe 2000. Once you have air sealed and properly insulated the ductwork, you should take steps to keep them cleaner. The AirSafe 2000 Furnace Filter comes in all sizes including custom sizes. Click here to learn more or call (865) 484-6653.

About Michael Church

Michael Church has been involved with indoor air quality since 2005 and feels the unhealthy crawl space is one of the major problems causing poor indoor air quality.


  1. Linda on July 8, 2018 at 10:23 am

    Thank you so much for your expertise and information! I would be considered a novice, however money being the main motivator I will be doing this on my own!

    So I will watch your video a few more times make my shopping list and off to the Big Box store to buy supplies!

    Thanks again, Linda

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