Taping furnace air ducts
 

The other day I came home to a 60 degree house. The thermostat is programmed to start warming up the house to 69 a while before we get home, so I knew something was wrong. Tonight, I finally got around to checking it out. Oddly, the furnace was keeping the house around 60 which is what we keep it at night and during the day when we are at work. Anyway, I found a totally clogged air filter. I was surprised because I hadn't changed it all that long ago, or so I thought. Replacing the filter fixed the problem (likely overheating the burner tripping a sensor to shut the furnace down.

While I was down there, I took some time to inspect the air ducts. This was long overdue as I've read quite a bit on how leaky duct work can cause huge increases in energy usage. I always figured I had so little exposed ducting that it wouldn't make much of a difference. After inspecting the duct work, I'd say I was pretty wrong. Here is what I found:

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So, I figured now is as good a time as any, so I ran out to the garage and grabbed my aluminum tape that I had gotten to do this earlier. Remember, you can't use normal duct tape for taping heating ducts.

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Here is an overview shot of what I have downstairs. The duct on the left is a return line, so slightly less important than the ducting going straight up, but still important.

You can also see my horribly dirty air filter in the garbage. :o

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The one roll of tape went an okay distance, but I definitely need another roll or two to finish up. I was able to get all around the base of the duct to the furnace which had some fairly decent gaps and as you can see a lot of corners had huge gaps. I really don't understand why this stuff isn't required at install.

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I got my foil backed duct tape at Home Depot. It was a 60 yard role for $15. It seems kind of pricey, but it had both HIGHER and LOWER temperature ratings and was LONGER than the stuff at Lowe's, not to mention a dollar less. I used it to do some duct work and when building an insulated attic/stair cover. I still have lots left over for future work.

Also, if you heat your basement, I don't understand why you are sealing the gaps when you have a vent coming out the side of the ductwork. To keep the same basement temp you will need to open the vent more to compensate for the loss of gaps. If you don't heat your basement, you should also look into covering the vent, not just closing it off, and insulating the ducts and ceiling down there. Just be careful if you start insulating things that you don't wind up with it getting so cold that water pipes would burst.

Good point about the vent. I do not heat the basement. The vent is there... I don't know why. :) I'll be looking into sealing it off.

I bought a roll of aluminum tape a couple of years ago, and it was one of the best cheap purchases I've made. I love the stuff. It comes in handy in a surprisingly large number of random jobs. I sealed off my ducts as well as I could a couple years ago, and also sealed off two vents in the basement with this tape. It's still holding strong two years later.

Everyone raves about the hundred of uses of duct tape. If duct tape has a hundred uses, aluminum tape has at least 200.

I dropped by the home improvement store the other night and picked up a new roll of tape. The one pictured above was 10 yards. It cost about $2.50. The one I picked up last night was 50 yards for $7.50. We'll see if thats enough to finish up all the taping.

As a side note. Its probably mostly from the filter replacement, but my house heats up a lot faster now. I had previously been getting home and the house was 62-66 (up from 60) degrees. At that point, the furnace had been on for almost an hour! Last night I got home about 20 minutes later than normal, but the temperature was already to 69. Mental note, reeeeeeeeeally make sure to check your furnace filters! Taping doesn't hurt either. :)

I continued on the taping yesterday morning. I've basically gone and taped any and all joints that I could get to. I did find some dandy leaks too.


I popped off the vent that Wyatt suggested covering up. This is the view of a connection that basically goes to the other side of the basement and just dumps air downstairs. For an unheated basement its completely useless and leaks air to boot. If I didn't have the flash on the camera you could see light through the joint.
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This is the outside all sealed up with a plate and some tape.
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Then I put a plate over where the vent was and taped it up too.
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Next, I found this beauty. It had been 'sealed' with regular duct tape that had long ago lost adhesion.
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Peeling back the tape I found this.
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So, I cut back the duct tape as well as I could.
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And I tried sealing it up with the aluminum tape. It seemed to stick to the wood alright but I'm unsure how it'll hold over time. For now, its better than leaving nothing there. If you have any good ideas here let me know. I had thought about cutting up a sheet of metal and screwing into the wood on each side making an L shaped piece.
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Then, I noticed something else right below this. A piece of lathe was blocking my view of the edge of the ducting. So, I pulled it away. Look, another huge gap.
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So, more tape!
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I kept going and most of the other stuff wasn't as bad. I wasn't able to get at hardly any of the tops of the vents that ran horizontally though and I wish I could get at them.

Good job! I did the same a few years ago.

What I found really disconcerting was how sloppy the duct installation was. Looks like the installer used a can opener to cut the metal.

Haha, that sounds like a pretty accurate description hhhpppp.

BTW, welcome to the site.

I continued the taping this morning. This time I moved to the first floor where my largest (and I think only) cold air return is.
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I quickly found out that the duct isn't directly connected to the cold air return though. The vent drops down and the only opening is what you see here (minus a 1" gap on the other side just open to the basement that I taped up). It looks like someone measured wrong and cut into the floor at the wrong point.
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So, I removed the piece of sheet steel on the side. I felt around behind it and felt nothing so I wondered why it was there. This is what was behind it. I still have no idea why it was there...

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Oh, but what is this? I see light. Yeah, thats the basement. My main cold air return had a HUGE leak into the basement.
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So, I re-bent the piece I had taken out and pushed it to the end of the cold air return. This picture is looking up from the basement. You can see how large this leak was.
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I then bent up a new piece to go next to the old piece to complete the block off.
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I then taped it up as best I could.
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Then, I went back upstairs and taped up as much as I could on the other side.

Its far from being perfectly sealed, but its definitely a step in the right direction. I'm hoping to put a new floor in this room in the not too distant future, so I didn't try to get it perfect. I'll fix it when I get around to that project.
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Well, that last bit of duct sealing really did something. I'm not exactly sure why (feel free to comment), but the air coming out of the ducting is now coming out at a much higher velocity than before. I hadn't noticed this on any of the other taping sessions yet, but this is quite drastic. I imagine that is a good thing?

Our 1948-vintage home was retrofitted with central heat & air decades ago, using the uninsulated exterior wall cavities for return air. Likely a code violation even when done, I don't know. Of course, at a later point, someone blew in insulation into the walls. Two great things do not always make a peanut butter cup.

We bought it in '98, and the HVAC kicking on would SLAM the basement door closed, as the stairway had become the primary return air, presumably using leaks and vents in the basement to get that air into the flow. Geesh.

We have done extensive renovation and added enough returns that there is little draw down the stairs now.

I do have a heated basement, but will evaluate the need for taping in the basement and attic this spring.

Great site, Daox. Cannot believe I just found it from a Jough96Accord post on cleanmpg.

Welcome to the site ksstathead. Great to have you here. :) Feel free to post an intro. We'd love to hear about your home and what you've done with it.

Thats quite the situation with the basement door! I too noticed that while on the stairs plus the furnace being on there was a really decent draft. Not enough to slam a door, but enough to really feel standing there.

I do heat my basement but I'm thinking of taking the time to tape all of the joints just to keep that air velocity high.

As well the outlets are where they are for a reason. Dumping hot air in the middle of my work area at ceiling level may technically make the room warmer but it's far from the most effective way to make me feel warm.

Total total noob here - new to the site, and new to renovations. Right now we are not renovating so much as we are chasing problems. Today's problem is HVAC. There are leaks we have to deal with that make Daox's look dainty. One gap in particular - where there's a penny inserted in the photos here, we could shove a 2x2 in ours.

Lots of taping to do.

Years ago, I found an article on tapes and sealants that concluded that the absolute worst tape for taping ducts...is duct tape. I found the article again, here (I can't post links yet, sorry):

I am wondering if there are new appraches or standards to consider. The article is now 12 years old... green approaches preferred, but right now, filling the big gaps IS pretty green, almost regardless of how we do it.

I would just use sheet metal and aluminum tape.

I just got around to perusing the forums for morsels of info to help me on my way, and I find this thread. :) Another example of why I thoroughly like this site.

I am often amazed at the quality(?) of work performed by a person paid to do a job. It's exactly why I try to do the work myself if at all possible. Most of the folks that regularly come to this site could do better work than the sloppiness you found. The energy savings you have just secured make you wonder why the previous owner hadn't done this and the light switch mod you recently took care of. To both of those improvements, I say "well done." :thumbup:

As for the extra velocity of the air coming out of your vents, it had to increase. You increased the volume of air that made it to the vent registers by removing so many outlets where the blower used to push the {somewhat} conditioned air. Less leakage means more, and better conditioned air to the registers. I'm certain there is a pleasant surprise coming on the power bill, if you can compare it to what it used to be.

Doax you showed in one pic were you filled a gap that put some of the aluminum tape on the wood...you could just put a strip of duct tape across the edge of the aluminum tape to hold it to the wood.

Of course your post is a few months old so if its still stuck it probably won't go any were.

Hey all,
My company sent me to a HERS Rater (Energy Star) class. We had a discussion about Sealing Products for ducts. The only product better for sealing ducts than the UL181 Aluminum Tape is UL181 Duct Mastic. UL181 Duct Mastic is a peanut butter like substance when you apply it. It hardens in a couple of days to a flexible hard rubbery seal. It sticks to metal, plastic, and wood. It remains affixed after ul181 tape has sweated off or cracked.

You apply it with a paint brush or gloved hand 1/4-3/8 thick. Push it right into the Crevasses. Larger gaps may need some mesh tape for a binder.

Does the mastic require a cure time before running the HVAC, or can you keep it in operation the entire time?

I tried to find mastic before going with the tape and I could not find it at the local stores.

As far as using Duct Mastic on an operational system. You would want the system shut down for a while. But the stuff we use here in the factory is normally good to go in 24hrs. I'm sure the label on the tube/bucket is your best friend though.

Last year when I was going to do this to my house there wasn't any in stores either. I bought it from the modular factory where I work. But when I was reading this thread I looked on home depot site and it lists a tube and a 1/2gal. bucket of air duct sealant. I think the stores are coming around to the fact they have to start carrying this stuff.

Just a quick update on this. While I was insulating my pipes last week or so, I took another look at this to see how it was doing. Everything is still sticking and sealed fine.

That was some major improvements in covering up air leaks.

Keep an eye on the aluminum tape where it attaches to the wood. Mine held for about three years but eventually let go.

I was actually just in my basement and took a look at some of my taping done 8 years ago. Most of it is still good, but there are definitely area that are leaking large amounts of air again. Time to revisit things!

a quick and dirty reinforcement might be a couple of T50 staples across the wood/tape mating surface.