Several months ago I did a Toolbox Tuesday on the proper tape to use when sealing up your ducts. In spite of its name, duct tape is not the tape of choice, go figure. But since that post, I've used one other method for sealing up our ducts that I've not used previously, and I want to share that with you today.

As you may have noticed, we've been spending a significant amount of time in the attic working on our duct work. After my discovery of the giant hole in the side of our air conditioner's main duct trunk, I've been on a mission to seal this puppy up and make our air conditioner run as efficiently as possible.

Until recently I've been relying almost entirely on the foil tape to sure up all of the leaky and horrible joints. When I run across things like this, I'm glad I'm finally hunting down and fixing all of these problem areas.

Yep, that's a patch with a patch on top of it, just screwed into place with no sealant, tape, or ways to secure it beyond the screws. Do you want to place a wager on whether or not I could feel cold air blowing out almost completely unrestricted near this spot? Who were these guys that installed this air handler? Oh right, I know just who they were. I won't be calling them anytime soon. That's some clown ductwork, bro, that's for sure. 

Beyond these glaring holes and giant problems, every seam in the duct work is leaky and loose. While tape has worked wonders, it's a little slow and tedious, especially in tight areas. Recently I started to use something different, and I learned about it while watching This Old House (TOH).

My HVAC and Plumbing Hero, Rich Trethewey

Our favorite TOH plumber, Richard Trethewey, was raving about the efficiency of the newly installed forced air unit on the most recent season of TOH and touched on the use of the sealant rather than tape. This sparked my interest enough that it got me to pick up a bucket the next time I found myself aimlessly wandering the aisles of Lowes (okay, it happens more frequently than I care to admit). Who says product placement is ineffective?

The truth is, I've had this bucket for a couple of weeks, but I've been a little stubborn about using it. Perhaps it's the grumpy old man in me starting to come out, but I figured "tape works fine for me, so I'll keep using tape, hrmph." How stupid is that? I mean, I bought the stuff, so why didn't I want to use it. Sometimes I even shake my head at myself. 

Last weekend I finally got over my crotchetiness and, while sweating my tail off in the attic yet again, decided to give the stuff a try. Using a wood shim as my applicator of choice, I began applying the somewhat thick and sticky substance.

I applied this magic goo to the various seams and corners that had yet to be treated with tape, then even applied it over top of the tape in some places. You know, for good measure. The photo below is actually from the second coat I applied after the first coat had dried. Again...for good measure.

I was quite happy with how easily it went on, how well it filled gaps, and with the seemingly air tight seal it left. I started to wonder why I hadn't been using this stuff all along?

Ideally, the duct installer would use this on the various pieces of duct prior to installation, and it would ooze and work its way through the various joints. But with our situation, we'd have no such luxury. This was a pure and simple attempt to fix a sloppy and bad job without tearing the whole system apart. I was worried I would turn the AC on after letting it cure and it would all just blow off, but I was hopeful that wouldn't be the case.

After allowing about 36 hours of the reccomended 48 (it just got too hot), I nervously fired up the AC. After a few minutes I crawled up into the attic to check my work. Holding my hand near the area of the duct that had previously been spraying money cold air into the unconditioned and sweltering attic space, I felt...nothing. Yes! Nothing! The sealant hat worked and our main duct trunk was shockingly sealed. 

The sealant had formed a dark plastic/rubbery barrier to keep the cold air in and the attic hot, the way it was supposed to be. No longer would we be paying to keep our Christmas decorations nice and cool. It's Santa's turn to sweat a little this summer.

With my newfound knowledge and experience with this newfangled duct sealant, I'll be able to surely make quick work of other similar HVAC upgrades. I hope this bit of information is equally as useful to you and helps you achieve a home with maximum efficiency.

Have you used this duct sealant in any of your projects? Have any advice or experience you'd like to share on its use? Though the first step of my project is done, I have many steps remaining where a little friendly advice can help tremendously.

Did you enjoy reading this post? Want to learn more about our first-hand experiences with other tools, devices or items used throughout our renovation? If so, check out our complete list of product reviews in our Toolbox Tuesday section

Note: We weren't compensated for this review. We simply want to share good products when we see them, and hope that learning from our mistakes can help save you time, money and frustration.

Comments 9


6/19/2012 at 10:35 AM
I am the same way! I ordered that Wood Epoxy stuff you recommended and its been sitting in my basement since I got it, waiting to be used. I bought the damn stuff, why not use it? Some day soon if I'm lucky :)

I really love your blog because of things like this. You use the products and test them. So now the million dollar questions is if you are you planning on using any duct wrap to finish? I'm dying to know what you choose if so. We have similar square (and even some round) ducts in our rubble basement from our heating system. I definitely want to prevent them and the water lines from freezing in the basement (or condensating in the summer) and am researching duct wraps and pipe wraps lately. Frost King appears to have the pipe wraps, but the duct wraps I'm not sure about.
Duct wraps are the next things we'll be looking into, so we'll be sharing the route we take at some point in the near future. I'm glad you took our advice on the epoxy, and I'm very glad you find these posts useful. Makes me want to keep doing them.
6/19/2012 at 10:52 AM
What happens if this stuff has to be taken off? Do you think it will peel away pretty easily?
From my experience in removing it from my hands, it seems to come off with a little effort. In other words, I think you'd be able to scrape it off if you needed to, and you'd probably be able to remove it more completely with some sort of alcohol or something. But I'm just guessing here.
6/19/2012 at 2:37 PM
Keep an eye on the ducts and whether or not you'll have condensation now. Before you had cold air in a metal duct surrounded by slightly less cold air because of all the leaks in the ductwork. Now, you have really cold air and cold metal surrounded by really hot attic air. Your Delta-T is now a lot bigger. Will you have sweaty ducts with lots of condensation (like a glass of ice water on a summer porch)? Whereas before, you had a glass of ice water in a refrigerator (not much condensation, if any).

I'm no HVAC expert, but something to watch out for. See Lstiburek. You might have to insulate the hell out of the ducts to keep the cold ducts away from the hot humid attic air.
This is a really, really great point, and on our checklist of things to address. Now that we've got all of the ducts pretty well sealed (maybe a few spots left), we're going to be insulating around the ducts to hopefully prevent this potential issue of sweating. The majority of the runs of duct are the flexible and insulated duct work, so it's a matter of wrapping this main duct trunk.
Katia Galarraga
6/19/2012 at 8:59 PM
hi, not available in home depot :(
6/20/2012 at 10:59 AM
It looks like it will hold, but I'd keep an eye on the ducts for condensation build-up. If you had to remove it down the road, it looks like you would scrape it off like caulk.
6/22/2012 at 1:46 PM
If HD doesn't have it (no surprise there) try ABC Distributors in Shirlington near Weenie Beenie. They're only open weekdays though.
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