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Thread: Leaky ducts

  1. #1
    Join Date
    Dec 2006
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    Leaky ducts

    Hello again. Got another dumb question. I am sealing my house as best I can (more insulation, door seals, etc) and I am going to try to seal the ductwork in my attic. I have read up on mastic, but which one is better...tape or the caulk? What is the way you guys have found works best on this process?

    On that same note, the guy who installed the system strapped three supply lines to the roof framing, and it pinches a little. Would it be okay to finish sealing those, unstrap, lay them down and put some loose insulation on top of them?

    Thanks for any help.

  2. #2
    Join Date
    Feb 2003
    Location
    Huntsville,AL
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    I used mastic -- simple, cheap, easy to get into tight spaces -- covers large gaps easily

    sounds like you have flex duct -- best to keep such straight --
    BUT, for that matter, this statement is true for any fluid flow! -- use smooth bends, wye fittings; keep bends close to source --
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  3. #3
    Join Date
    Aug 2006
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    combination

    I'd suggest a combination of brush on Mastic, mastic in caulk tubes, and also metal tape with a mastic backing. Should be able to seal about anything you might run into.

  4. #4
    Join Date
    Jan 2006
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    duct tape

    For about twice the cost, you can buy a metal (tin foil) faced duct tape. Seems to last longer and is incredibally sticky. From a duct work supply house.

  5. #5
    Join Date
    Jun 2005
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    Northeast USA
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    I have found Home Depot and Lowes carry the metal tape and were cheaper than retail price at a local HVAC supply house. Both had two types of the tape, the standard metal tape and metal tape with a weather seal layer.

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Caution when adding insulation to the outside of an a/c duct. Attic air is high dew point. Added insulation lowers the duct surface temperatures. If the attic air penetrates the added insulation, condensation occurs at the duct surface under the insulation. If wet for a couple days, mold grows producing musty odors. So additional insulation requires an air tight moisture barrier on the outside of the added insulation. Allowing cold ducts to touch other ducts or attic insulation causes lower duct surface temperature. If below air dew point, condensation results. Thats why it's good practice to suspend insulated ducts in high dew point air. Better to provide additional support to lesson the kink. TB

  7. #7
    Join Date
    Mar 2003
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    Duct Sealing

    Hi helmetheadbob,

    I'm glad to see you are taking an interest in sealing up your duct system as well as the home weatherization.

    Did you know that the Federal Government has a Tax incentive program for energy efficient upgrades to your home?

    http://www.epa.gov/greenbuilding/tools/funding.htm
    http://airsystemsplus.biz/support/Fe...Tax_Credit.pdf
    http://www.energytaxincentives.org/t...ool-equip.html

    Other entities such as Utility Company's, Private Grants, and State and Local Government may have incentives, rebates and such too. Call them!

    Here in California, we have a governmental department dedicated to Energy conservation known as the California Energy Commission. The CEC published a simple one page document that I think will justify your return on investment for sealing ducts.

    http://airsystemsplus.biz/support/20...QUIREMENTS.PDF

    The CEC also published videos available online that show you have to do these energy efficiency tasks.
    http://www.energyvideos.com/blda.php?P=CA&A=5&S=res

    It's important to note a tight home can cause indoor air quality issues too!
    Since you're DIY, you'll save on the contractor fees but I urge you not to stop there. Have a H.E.R.S (Home Energy Rating System) rater test the ducts for leaks after you done. Also, they can pressurize your home to determine how tight it really is.

    Also, consider a really good central electronic air filtration system coupling into your existing forced air unit. The two links below
    are the best known electronic air filters (purifiers) on the market. Maybe other HVAC-Talk members will contribute their experience with these on other air filter products. Please note the Carrier/Bryant are the same company with different logos as well as Trane/American Standard.

    http://www.bryant.com/products/perfe...purifier.shtml
    http://www.trane.com/Residential/Cle...anEffects.aspx

    I'm included some helpful and interesting links below.

    http://www.homeenergy.org/index.php
    http://www.calhomeperformance.org/index.html
    http://www.energyquest.ca.gov/index.html
    http://www.energy.ca.gov/index.html
    http://www.consumerenergycenter.org/index.html
    http://www.energysavings.honeywell.com/home.html
    http://www.energytaxincentives.org/t...ool-equip.html

    Checking for all leaks:
    Buy some "Smokies" which burn for about 75 seconds and emit a safe fog. Open all the windows in the house. Tape up the registers grilles so no air gets out (Use blue painters tape). Light the smokey and turn on the indoor fan for about 3 seconds. The fan will run about 15 seconds. Check the ducts for smoke leaks.

    TAPE or Mastic or Caulking:
    These are three different sealing methods for three different applications.

    TAPE:
    Only use UL-181B-FX printed 3 mil tape. This tape is good for flex duct and metal. You DON'T need foil tape any longer. See the energy video under HVAC. Apply the tape liberally onto any seam or air leak.

    MASTIC: Use indoor rated "Glen Kote DP1010" referred to in the trade as "Pookie". Use a 2 inch wide disposable brush to apply. Also recommend gloves and long sleeve. It's a bit messy.

    Apply to small seams/cracks on metal to metal and metal to duct.

    See: http://www.hardcast.com/products/pr_detail.asp?pid=1

    Caulking: Use a HVAC/R rated type caulk. It's cleaner to work with but with the tub of pookie, you most likely won't need it.

    See: http://www.socalgas.com/construction...%20Sealing.htm

    Duct Straps: Use to tighten the duct on the inner lining to the start collar or t-wye and on the outer insulated sheath. Two straps per connection.

    See: http://www.cable-ties.com/rtapplication.htm

    PLEASE NOTE:
    Although I attempted to cover all the aspects of a duct sealing job, I would not consider this a last word. Other members my add or comment to what I've written herein. Just like any project, it's always a good idea to consult with an experienced professional. And remember, just because some may have a license, doesn't mean they are an expert.


    Good Luck!

  8. #8
    Join Date
    May 2007
    Posts
    164
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    Checkin for Leaks?

    Is this still 1 of the best method to check for leaks?

    Checking for all leaks:
    Buy some "Smokies" which burn for about 75 seconds and emit a safe fog. Open all the windows in the house. Tape up the registers grilles so no air gets out (Use blue painters tape). Light the smokey and turn on the indoor fan for about 3 seconds. The fan will run about 15 seconds. Check the ducts for smoke leaks.

    I have all flex in my attic here in hot AZ and are smokies safe and can homeowners get them?

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