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Blown in air duct sealing and individual run testing

user-943418 | Posted in General Questions on

My home has return air in the attic which is relatively accessible and supply air in the crawlspace, some of which isn’t very accessible. I had a blower door and ducting tests that revealed huge leakage. we applied mastic to everything accessible and fixed a big leak. We retested and got down to about 25% leakage and at the point the contractor said it was the best they could do.

The duct work is all metal with insulation. We have return air everywhere there is supply air and the home is 3400 sq ft. We have a lot of duct work. Tearing all the old insulation off to seal the joints seems excessive when I don’t really know what is causing the leakage. It may be in inaccessible runs most likely in supply areas.

Two questions; Does the spray-in duct sealing work? Second, Why cant mechanical contractors isolate the leakage side, supply or return, or isolate the individual runs? It seems a simple matter of pressure reading but what do I know?

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  1. davidmeiland | | #1

    In most cases you can partition the air handler with cardboard and masking tape well enough to test the supply and return sides separately. You can also get a general idea of which side has more leakage when the blower door is set up, by running the air handler and watching what happens on the manometer.

    In your house, was "total duct leakage" tested, or "leakage to the outside"...?

    I've heard about Aero-seal or whatever the duct-sealing process is, but have no direct experience.

  2. Danny Kelly | | #2

    You can test for duct leakage with a blower door and pressure pan. Run your blower door like you typically would and take a reading at each supply/return register. Since your ductwork is supposed to be a closed system - you should get a reading of 0 at each register in an ideal world. By doing this you can often find the few runs that have the most leakage and concentrate on those. An experience BPI contractor can help with this.

    Not very familiar with the spray in duct sealing - someone had mentioned that to me the other day and I was a little skeptical. Although if it is cheap to do - may be worth a try, I wouldn't spend a lot of money on it with talking to some people that have used it before.

  3. ARF9VudJeZ | | #3

    a good mechanical contractor or building analyst SHOULD be able to isolate which side is or return. A Half-Nelson duct leakage test should give the answer, but should be handled with care. Tape off all registers, then turn the AH fan on for a brief period. Insert pressure probe in both supply and return plenums. Whichever side is at a lower operational pressure, as measured with manometer while the fan is ON, is leakier. Don't leave the fan on for too long, and use care if the trunk is made of duct board.

  4. ARF9VudJeZ | | #4

    They were working on this stuff and publishing it decades ago......

  5. capnkent | | #5

    Not sure what you mean by 25%... does that mean you improved the lakeage by 75% - if so that's pretty good!
    Whoever did the duct testing could identify the areas better - as Danny Kelly mentioned above, the pressure pan will give you good idea of the worst areas. We look to get readings of 1 or below... anything more indicates too much leakage in that area. Seen numbers in the teens!
    We've usually found that it is a lot of small leaks throughout but occasionally find a disconnect or large gaps.
    I have talked to several officials and tradespeople who know of a local comapny that does interior duct sealing but apparently it is rather cost prohibitive for most residential applications... usually cheaper to remove insulation, seal ducts and replace insulation rather than pay for the the interior sealing system...

  6. user-943418 | | #6

    Aero Seal is the product I heard about. It's been around awhile but doesn't seem to have caught on. I cant seem to find much in the way of negative reports, or positive. We have one contractor here (Ft Worth) who I talked to. You have to have the ducts cleaned, then sealed. 4k rough estimate for my house. I cant imagine getting every 4 foot seam and the lengthwise seam sealed on all the duct-work I have for under 4k actually.

    Thanks for all the ideas on isolating the ducts. I thought it could be done but neither the energy audit people or my energy saving contractor knew how. If anyone knows a good contractor here in the DFW area that can narrow down the problem that would be most helpful. (I have talked to two Heat and Air contractors who didn't know how. In fact they shrugged their shoulders and said that much leakage is normal.)

  7. davidmeiland | | #7

    My guess is that Aero Seal hasn't caught on because it's expensive. The average person can barely understand duct leakage and the cost implications. As you have seen, many HVAC contractors aren't up to date either. The typical energy auditor can barely sell their services, much less the upgrades a typical house needs, partly due to the short-term mentality that most homeowners have, along with the lack of ready money for improvements. If you choose to spend $4K on duct sealing you will be one of the very few, and it might be an enlightened choice. Most will choose to bleed extra money every month as they pay their utility bill.

  8. Danny Kelly | | #8

    You can try searching the BPI database for a performance contractor. I would look for one with the Envelope Professional designation:
    You could also check the NCI website - they have good programs as well.

    If you try the Aero Seal method - I would recommend doing a before and after duct blaster (one of of the other tests mentioned in the article Art referenced and make sure they can somehow quantify how much they are going to improve the system, i.e. get the entire system to under 6% leakage to the outside, improve the conditions by X%, etc. and do not pay them until the "test out" shows significant improvement. If using a product like that, you may want to have them check the static pressure of the system afterwards as well to be sure it is within manufacturer's standards.

  9. user-943418 | | #9

    Art- thanks for the link. Very informative.
    Danny - we have one in Dallas that has the designation Envelope Professional?! The Aero Seal contractor does guarantee the work to a certain leakage.

    Overall, I'd say that finding a contractor to do granular diagnostics is hard. Everyone wants to recommend a comprehensive effort that catches the problem in the overall (expensive) solution. Seal all the ducts, replace all the ducts etc.

    I'm surprised no-one recommends turning the system on and using thermal imaging in the attic and crawlspace to find the leakage points.

  10. 2JX2f9pDwU | | #10

    Some great input here - some of it on the mark, some not so much. I work with Aeroseal and thought I would clarify a few things. The technology IS highly effective at sealing air duct leaks. There doesn't seem to be any argument about that. The DOE has called aeroseal technology one of the top 23 most important consumer technologies to come out since the agency was first established. It's also true that a lot of HVAC contractors are unfamiliar with aerosealing. While it's been around for a few years it has gotten little exposure. A new company dedicated solely to aeroseal technology was established earlier this year - they are working on changing that. The first order of business is getting more contractors educated, trained and licensed. As far as the cost, it's not free but it's less expensive than some here have suggested. An average home owner will pay around $1,100 - $2,000 to have their entire air duct system sealed. Not so expensive when you consider that it typically reduces heating and cooling costs by about 30 percent. Depending upon where the duct system is located, home owners save $250 - $850 a year on their utility bills. That means it's a lot less expensive and more effective than other energy conservation options such as replacing windows or retrofitting a new furnace/AC. And I'm not sure why someone was told air ducts had to be cleaned first. It's a fairly quick and unobtrusive procedure - in and out in a day. The bottom line is that it's the only way available today to effectively seal entire air duct systems. I suggest anyone interested in the facts check out the aeroseal website or call an HVAC pro that offers the service. Hope this was helpful.

  11. LuvHawaii | | #11

    We qre in the Pacific NW, decided to look into this product for energy savings, and called. The expert", who came out to our house to explain procedure, seemed very well informed. The techs spray a product into ducts as a liquid/aresoul, where itfills in holes, seals out leaks, and dries hard. we wanted to know about any smell, and off gassing. they would not tell us the ingredients (propriatary) but same stuff that is used in chewing gum, so very safe,we were assured over & over.... assured us very safe, there would be little or no smell, except for a very faint mild smell about an hour after spraying, and as soon as it dried, there would be absolutely NO order and no off-gassing when furnace forced warm air thru ducts. Our particular concerns were as follows: I am a cancer survivor, and am left with mild asthma & immune system sensitivities. My husband is on immune suppress for RA, and also mildly chemical sensitive. Otherwise, in very good health. We were again assured (!!!! )that there were no harmful ingredients...totally safe for our situation. they really sold the product hard. I found nothing online but good reviews, so we signed up. the guys who came out that did the work were real nice, but within and hour after starting the spraying, a horrible burt plastic smell overwhelmed the house. My eyes & troat were burning, I became sick to my stomach, and light headed, had to sit outside in winter storm to get away from fumes & recover. this went on all day. was told it would dry & smell would didn't!! they said leave the furnace running for 2 hours, with windows wide open, until product dried, and smell would stop. IT DIDN'T! . after serious research (I should have done before signing up..) I found that the product was a glue, made from 2E1H (look it up, it is a common industrial solvent), and vynal acetate polymer (VAP). sounds less appealing than "chewing gum", right? no proven as carcinogenic, but DOES off gas, (sick building syndrom) does smell, and has proven to have caused problems in animals immune systems. We were mislead, and sold a product that has cause us big health problems. still negotiating to have contaminated ductwork removed & replaced. I would NEVER recommend this is too new, and possibility of long term health issues have not been addressed.

  12. duffeymt | | #12

    C Dickson, do you still have this issue? We are looking into this product and have a small baby and 2 dogs in the house.

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