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  1. #1
    Join Date
    Aug 2012
    Location
    VA, USA
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    48

    Foaming ductwork

    What is your opinion on foaming ductwork (2") on top of existing insulation?

    Quote Originally Posted by energy_rater_La View Post
    you won't hire someone to unwrap & insulate and rewrap duct system for price quoted in foxbusiness link.
    maybe one or two ducts.

    in some climates burying ducts is recommended.
    ducts in attic waste more than 15%, but architects, hvac & homeowners
    still do it.

    believe me..if there was a product that provided R-20 ductwork..
    hvac supply would stock it, and some hvac companies would install it.
    some homeowners would pay extra cost to have it.
    sadly..it just doesn't exist.

    think of how big & thick the insulation would be on the ductwork. R-19
    is 6"..in attics where space is premium & compressing the insulation
    derates it..how is it going to work??

  2. #2
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    Sep 2008
    Location
    Western PA
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    25,869

  3. #3
    Join Date
    Dec 2010
    Location
    Down by the river
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    1,673
    It would be a better job to rip off old insulation then foam. You would have superior insulation as well as sealed

  4. #4
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    7,669
    Quote Originally Posted by Southern Mech View Post
    It would be a better job to rip off old insulation then foam. You would have superior insulation as well as sealed
    X2

  5. #5
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,443
    Quote Originally Posted by Southern Mech View Post
    It would be a better job to rip off old insulation then foam. You would have superior insulation as well as sealed
    X3

  6. #6
    Join Date
    Aug 2012
    Posts
    83
    I think the original poster is talking about flex duct? since the duct is the insulation you really can't rip it off.

  7. #7
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,756
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  8. #8
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,289
    I never recommend foam for ductwork. ever.

    foam, when sprayed is thin, then it expands rapidly.
    it doesn't always fill in the cracks where seal is needed.
    mastic on the other hand is applied with a brush
    which pushes the mastic into the cracks. where the ducts leak.

    on the jobs where I've seen foam on ducts some of
    the problems were:
    that there were areas that the foam did not seal
    maybe ductwork was wet, or dirty or mix or temp of foam was wrong.

    varying depths of foam, from 1/8" to 3"..and everywhere in between.

    if ducts are wet, foam encapsulates moisture.

    if attic is insulated with conventional insulation, foam can encapsulate
    this insulation next to gaps where supply boxes meet attic floor,
    on top of the supply boxes & at return plenums.

    foam often has voids, I call them honeycombs, where there are large
    bubbles in the foam. these areas de-rate the performance of the insulation.

    on most of these foam ductwork homes, the reason I was there was because
    of problems created by foam insulating the ducts.

    most foam companies may spray foam while on the job to spray something else..
    be it attic floor, roof..under house. but just to spray ducts takes a lot of time
    the company could make more money on..at another job.

    once the truck arrives on the job, the foam has to be heated to the right
    temp, set up for install takes time. most companies aren't going to go
    through all that for minimal monies when they can invest the same time
    on a job to make maximum monies.

    over the years I've worked with many foam companies.
    online things like 'buttering' the stud bays of walls..(1" inside studs of walls
    to air seal and then wall insulated with conventional insulation)
    are touted as good installs, and they are. but itrw..or at least here in La.
    no company is comming to just air seal. they come to do the full job,
    and turn small jobs down.

    I saw the study of the foamed ducts in the original thread.
    IMO it is another of those things that may be a good idea
    but have little real world application. unless foam company
    worked with a production builder and could do several
    installs within the same area.

    if foam was an acceptable sealant for ductwork, it would be
    listed as an approved product for this work. it isn't.
    there are good reasons for this, other than the problems
    I've observed in my inspections.

    given the mistakes I've seen in foam install jobs,
    I'd not let them near my ducts or equipment.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  9. #9
    Join Date
    Aug 2012
    Posts
    83
    Just for clarification the study recommended foaming ducts to increase R value/insulation value allowing ducts to be burried in loose fill insulation and prevent condensation in humid environments. . It never recommended foam as a way to seal flex duct which only needs mastic sealing on the ends anyways.

  10. #10
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,371
    If you're going to call a foam spray rig out to your house to foam ducts, switch gears. Foam the roof deck instead. Foaming ducts is like pumping bilges on the Titanic with a hand pump.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  11. #11
    Join Date
    Aug 2012
    Posts
    83
    I got a reasonable quote from a company that would just bring out a couple of disposable foam tanks 50 pounds each, no need for a whole truck!

  12. #12
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,371
    Newstudent, since you did not start this thread, you should not be posting in it. That's according to the AOP rules. I'm not a moderator but am compelled to point this out to you, as your posts in this thread may be deleted.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  13. #13
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,289
    so you'll oversee your sisters install in florida?
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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