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Daox 02-23-10 09:03 PM

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:

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.

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

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.

wyatt 02-24-10 11:53 AM

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.

wyatt 02-24-10 12:00 PM

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.

Daox 02-24-10 12:17 PM

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.

mincus 02-24-10 08:18 PM

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.

Daox 02-26-10 09:24 AM

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. :)

Daox 02-28-10 08:01 AM

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.

This is the outside all sealed up with a plate and some tape.

Then I put a plate over where the vent was and taped it up too.

Next, I found this beauty. It had been 'sealed' with regular duct tape that had long ago lost adhesion.

Peeling back the tape I found this.

So, I cut back the duct tape as well as I could.

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.

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.

So, more tape!

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.

hhhpppp 03-04-10 09:39 PM

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.

Daox 03-05-10 04:53 AM

Haha, that sounds like a pretty accurate description hhhpppp.

BTW, welcome to the site.

Daox 03-06-10 01:40 PM

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.

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.

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...

Oh, but what is this? I see light. Yeah, thats the basement. My main cold air return had a HUGE leak into the basement.

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.

I then bent up a new piece to go next to the old piece to complete the block off.

I then taped it up as best I could.

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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