How to test my furnace ducts.

Is there a DIY way of testing my furnace ducts for leakage? Smoke blown into the system? The professionals want several hundred dollars for testing ducts and I am not sure if I can trust them.
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Walter
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Hi Jim
Thanks for the input. However, sealing leaks with duct tape is about the worst remedy for leaks. According to the experts, anything but duct tape should be used to seal furnace duct connections.
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wrote:

Use duct mastic. Kind of messy but it will seal them up tight.
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says...

Even easier is to use aluminum foil HVAC tape. It's _not_ duct tape (which was never made for ducts) - it's tape meant especially for sealing HVAC ducts. It has a paper backing that you need to remove to expose the sticky part. It costs a few bucks a roll at any home centre (Home Depot etc), and if your ducts are accessible (i.e. in a basement), you can seal all the joints pretty easily. Just make sure to wipe off the ducts before putting the tape on (no matter how good the tape is, it won't stick if the ducts are covered in dust).
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Any pressure sensitive tape used on ducts should be rated UL181-A-P. It will be printed continuously on the tape, along with the brand & model of the tape and the last date tested. This is required by code. For flex ducts it should be rated UL181-B-FX, it will be marked in the same manner. Mastic should be rated UL181-A-M for rigid ducts and UL181-B-M for flex ducts. Accept no substitutes. These products have been tested for duct sealing purposes. There are other UL rated tapes, but even though they are sold as tapes for ducts, they do not meet code and should not be used for those purposes. Hope this helps.
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snipped-for-privacy@sccoast.net says...

I'm curious as to the difference between this tape and the "normal" foil metallic tape that's readily available.
I've got sheet metal ducting in my home, and I've used the "normal" stuff to seal up any air leaks where the ductwork is joined together. Prior to using the tape, there was nothing there at all, so there were minor air leaks all over the system. Regardless of UL rating, I would think that taping the joints (and sealing the leaks) would improve the system without any real drawbacks.

Beyond "not meeting code", what's the reason for using these specific rated tapes? I would think that in most residences the joints aren't taped at all, so some tape would be better than none (as long as the tape will stay stuck, unlike "duct" tape...).
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Normal duct tape is quite porous. The last thing you want. So while you will have reduced the leakage, you haven't eliminated it.
Secondly, you're supposed to avoid using flammables/heat decomposable materials directly in contact with duct (that's why the ducts are metal in the first place). The fabric-based duct tape will degrade over time.
Some HVAC systems are so finely balanced that using the correct tape may make a considerable difference in heat distribution.
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Chris Lewis, Una confibula non set est
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says...

I agree - by "normal" tape, I'm referring to the aluminum foil tape I can get at Home Depot for about $4CDN a roll (the manufacturer's web site for the stuff I'm using is http://www.tvmi.com/rfoil/tapes.htm ). There's nothing on it saying it's UL-approved, but it sticks very well to aluminum ductwork and seems to seal drafts really well.

I also agree - the tape I'm using isn't fabric duct tape, it's adhesive-backed aluminum tape.
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Just because it meets a rating dosen't mean it is the best available for the job; here is an interesting comparison http://www.energy.ca.gov/pier/final_project_reports/500-03-079.html
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By "normal duct tape", I was referring to the cloth backed stuff that you repair everything with. That Red Green has made so famous (you too can make a working elevator out of a phone booth, hot water tank, and copious quantities of duct tape). Or win thousands of dollars making sculpture out of it.
http://movies.go.com/parentpreviews/review?rid 1
[Can you think of another type of tape that's had a movie dedicated to it?]
As someone else put it, "duct tape is for everything BUT ducts".
Which is why it's important to be very careful in what you call it.
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The proper tape to use is a aluminized/metallic tape specifically intended for the purpose. Not classic "duct tape".
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Even some aluminum foil tapes are not acceptable. This is because they use a rubber based adhesive that degrades over time. The proper tapes have an acrylic adhesive that will last almost forever. You can redo the taping every few years, or just use the right stuff and just do it once.
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snipped-for-privacy@sccoast.net says...

According to the manufacturer's web site (http://www.tvmi.com/rfoil/tapes.htm ), the stuff I'm using has an acrylic adhesive, and it's cheap ($4CDN for a 30' roll).
So, back to my original question - what's the problem with using this type of tape, rather than the "UL-approved" stuff for sealing joints in aluminum ductwork?
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The UL rates stuff has been tested. so you know it will work. The un UL rated stuff has not, so you don't. That's the difference.
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says...

The stuff I'm using sticks really well, and has held up well over time - it's still stuck just as well as the day I applied it. I can't detect any air leaks near the joints I've taped, so it "works" as much as I expect it to. Before I applied the tape, there were noticeable leaks around those spots. As far as I'm concerned, the stuff I'm using works just fine.
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Check the temperature drop between the furnace plenum and the floor registers.
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