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Old 09-29-2008, 02:54 PM   #1
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Sealing up your Ducts


How important is it to seal up your duct work really tight if it runs in a heated basement?

My house was build in 1963. The ductwork was done very professionally, all bent and designed well. However there are spots where I can see that it has some tiny holes in it. I have been working on taping over all of the duct work with the nice shinny foil tape (regular duct tape is for the birds!). I've also been wrapping it with reflective foil insulation.

I opened up the end of the duct work, and stuck my camera into it and ran it on a timed exposure - so I could see where there were leaks.

The area that I see the most leaks that is hard to get to is on top of the main duct where there on the 90 degree elbows that tap off the main and route in between the joists. I can see little holes around where the 90's connect. It is hard to get to and I am not sure the best way to seal them up. Is there some kind of mastic, caulk, silicone, etc that I could get up there with and seal it up? Or is it not even that important?

Thanks
Jamie

EDIT: I went to home depot today and talked to a guy there, he encouraged me to just use the foil tape. He said the mastic stuff is hard to work with and messy and that it really won't gain much anything using it vs doing a careful job with taping.
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Last edited by jamiedolan; 09-30-2008 at 01:19 AM. Reason: new info
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Old 09-30-2008, 08:19 AM   #2
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Sealing up your Ducts


Continue to use the tape on flat regular smooth joints. Yes, mastic can be difficult to use, but works better on irregular joints and holds up better in the long run - won't tear from vibration. Also get yourself a small application paint brush with a stick/dowell taped to it to reach those tough areas.

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Old 09-30-2008, 12:42 PM   #3
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Sealing up your Ducts


You can't beat mastic. The Home Depot guy won't tell you to use mastic because they don't carry it.

I use mastic on all my HVAC installs. One because it is code (for a reason) and second it will last a long time.

Foil tape is only used for insulation sealing and not meant for sealing duct work.

But the way, duct tape is not the way to go so avoid that.

If you don't mind heating the basement then by all means let it be. If you want to get heat to the upper levels then tape all the joints. Anytime you have a hole this will cut the pressure of the air after that hole. If you have enough holes then you will have significantly less pressure at the end of the line. Your furnace will just run longer to get the area that you live in heated and will end up costing you more money.

Since most duct sealing is all about saving money then I would say seal all the holes. While mastic is expensive it will last for 30 years and energy prices will do nothing but go up and up and the relative cost of the mastic will seem like pocket change.
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Old 10-01-2008, 12:58 AM   #4
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Sealing up your Ducts


Quote:
Originally Posted by Marvin Gardens View Post
You can't beat mastic. The Home Depot guy won't tell you to use mastic because they don't carry it.
They have a tub of stuff that they called Mastic for duct work at home depot, it was about $11 for a 1/2 gallon size tub.

Well, I want energy efficiency, but I do want the basement and crawl space to stay at a decent temperature. I guess I will keep sealing up the ducts the best I can and then can add another vent if necessary.

Thanks for the information.
Jamie
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Old 10-01-2008, 01:16 AM   #5
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Sealing up your Ducts


Quote:
Originally Posted by jamiedolan View Post
They have a tub of stuff that they called Mastic for duct work at home depot, it was about $11 for a 1/2 gallon size tub.

Well, I want energy efficiency, but I do want the basement and crawl space to stay at a decent temperature. I guess I will keep sealing up the ducts the best I can and then can add another vent if necessary.

Thanks for the information.
Jamie
I use mastic tape. Not the mastic paint even thought that is okay for small leaks like in 90's and so on.

Keep in mind that there will be residual heat generated from the furnace that will keep the basement reasonably warm. Plus there is some ground warming that is constant year round.
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