Page 2 of 5 FirstFirst 12345 LastLast
Results 14 to 26 of 55
  1. #14
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,325
    The problem with wrapping any duct in an attic that already has a vapor resistant jacket (vinyl or foil) with unfaced insulation is that the unfaced section is vapor permeable. It is possible...how likely depends on several factors...that the formerly exposed jacket, now covered by permeable insulation, will cool to the dew point of the attic air temperature when the a/c is running.

    In the 1930's, very few ducts in houses carried cooled air...only heated.
    • 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.

  2. #15
    Join Date
    Apr 2001
    Location
    Over Here
    Posts
    1,105
    Quote Originally Posted by Shophound View Post
    It is possible...how likely depends on several factors...that the formerly exposed jacket, now covered by permeable insulation, will cool to the dew point of the attic air temperature when the a/c is running.
    Agreed. In the humid south, it is a common occurance every night for ducts in ventilated attics to reach dewpoint. Anything touching flex duct will cause it to sweat. Any sweat not evaporated (due to permeable insulation wrap) by the hot attic temps the next day remains to continue to condense the next night, leading to more saturated insulation.

    It is a very common thing for folks to turn their t-stats down at night to 68 degrees for sleeping which creates more opportunity for ducts to reach dew point.

  3. #16
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    " new student" implies an openness to learning. Hmmm. Genuine?

    In any event, +3:

    Quote Originally Posted by Shophound View Post
    It is possible......that

    jacket, now covered by permeable insulation, will cool to the dew point of the attic air temperature when the a/c is running.
    Resulting in a soggy, moldy, rotting mess in the attic.

    Run off half cocked and you may get lucky, or you may end up dealing with a litany of unintended consequences us "old students" warned you were lurking.

    There is a process. Taking shortcuts generally means missed opportunities and sometimes means expensive consequences.
    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.

  4. #17
    Join Date
    Aug 2012
    Posts
    83

    advice

    Quote Originally Posted by tedkidd View Post
    " new student" implies an openness to learning. Hmmm. Genuine?
    Resulting in a soggy, moldy, rotting mess in the attic.
    Run off half cocked and you may get lucky, or you may end up dealing with a litany of unintended consequences us "old students" warned you were lurking. There is a process. Taking shortcuts generally means missed opportunities and sometimes means expensive consequences.
    So basically what you are saying is that if I get condensation I should NOT wrap the ducts with insulation, but if I DON"T get condensation it is OK.

    So If I just spend $20 and get some insulation and wrap a seciton of the pipe and see what happens?

    Seems like no one really knows if it will make condensation.
    Obvioulsy water stain marks on the ceiling are an issue, but would wrapped insulation really get that soggy. I just can't imagine it staying soggy for long when the temperature up there is 120F or more.
    Her duct work is already sealed with mastic.

    Her budget doesn't allow for spray foaming the entire roofline.

    I've been researching this and radiant barrier and sealing up duct work are the top recommendations.
    Is there a product where you can remove the exsisting duct work vapro barrier and increase the insulation with a new vapor barrier, that would obviously work well.

  5. #18
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    Yeah, you want simple answers so you can take action. Unfortunately, the action you want to take has a lot of risk. Getting the details wrong may mean disappointing results, or worse.

    The first step is have a comprehensive home assessment. You are jumping from "high energy bills" to "cure specification" without the comprehensive diagnostics or cost benefit analysis step. Hyper simplification leads to disappointment.

    There are a huge number of dependencies. We can't see your house, and you don't have the necessary knowledge or tools to map them. Your focus on products rather than solutions is hard to break. Unfortunately, if you don't have the ability to step further away this will not make sense to you.

    You could take building science classes. But you'd still be short experience and $10,000 worth of tools.
    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.

  6. #19
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,164
    really ted? this is how you explain things & continue a discussion?

    I shouldn't have wondered aloud (aka in my earlier post) about wrapping ducts
    in unfaced batts. that was my mistake. sorry for sidetracking your post OP.

    OP,the problem with removing existing insulation vb jacket, and wrapping ducts with extra insulation
    and vb is labor & performance.

    there is no product to do this.

    with flex duct, removing the (vb) insulation jacket & wrapping existing insulation with
    another layer of insulation is at best difficult.
    then to seal the new vapor barrier would create another
    set of problems as to what materials to use...
    both for the vb and to make vb continous and sealed.
    certain tapes seal certain products. others fail quickly in extreme
    attic temps.
    you can imagine that over the years tradespeople and homeowners have tried
    different methods. none work well enough to be approved by acca.

    if ducts are suspended then air circulates around them and dries the condensation.
    ducts do condnesate in hot humid climates. there is no question of that.
    whether the homeowner feels/sees this
    or not is dependent upon what time dewpoint was reached, and what time homeowner
    makes the inspection.
    I usually find wet ducts early in the morning. however if ducts touch each other
    or lie on insulation on attic floor..then the condensation doesn't always dry.
    this is because the air does not circulate around the vapor barrier of the duct.
    wet insulation decreases the r-value of the insulation to 0. if the insulation
    doesn't dry, each time dewpoint is reached it gets wetter.

    if the air doesn't circulate the condensation doesn't dry. doesn't matter how hot the
    attic gets.

    correctly installed flex duct..straight tight runs with gentle curves rather than
    sharp drops and bends.
    ducts suspended with duct strap..not tight to the roofline, but suspended again,
    in straight runs with gentle curves & no restrictions..its an art in itself.

    as long as I've been doing this, I still have to
    step back and re-adjust the straps to keep ducts straight. now I know folks
    who don't..they get it right first time..but they've been at it longer than my 10+ years.

    personally I think sealing ducts, running & strapping ducts is as important as
    equipment install. but that isn't common thinking for most hvac companies.
    the person who does ducts is generally the low pay person on the job.

    I don't think anyone is saying if the ducts get condensation don't wrap but if the don't
    condnesate do wrap..that is climate specific information. as you can see from the link
    you posted in penn..it is ok to bury ducts in the insulation.
    but not in hot humid climates.

    the internet is great for info..but you have to consiter where it comes from. location wise
    and who is providing the info.

    radiant barriers do provide some help for ducts in attic.
    I have a rb, so does shophound. we have different types, but both of us
    have found benefit of this install.

    I do understand the cost of foam puts it out of range for a lot of people.
    so in this case, sealing the air barrier between the attic and the living space
    below, attic floor and ceiling of living space, is a good first step.
    once the air barrier is tight then you have less communication between the
    conditioned and unconditioned spaces.

    then mastic sealing ducts, supply boxes, plenums, plenums to equipment & r/a
    is step two.
    third step would be strapping ducts off insulation.

    adding rb if that is her choice, and more insulation on attic floor.


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

  7. #20
    Join Date
    Aug 2012
    Posts
    83
    "Unfortunately, the action you want to take has a lot of risk. "

    No it doesn't, worst case scenario, humidity is trapped and I'll blow $20 on insulation during a test.

    According to this article
    http://www.foxbusiness.com/personal-...ts-worth-cost/
    for just a little bit more than the cost of the energy audit I could hire someone to insulate the duct work.

    Below are some links to sample home energy audits. Why is it that none of them recommend increasing the insulation around duct work? When government studies and independent ones cite having duct work in attics is a 15% energy waster?
    http://www.nrel.gov/docs/fy10osti/48163.pdf


    http://www.carolinahomeenergy.com/re...uditReport.pdf
    http://www.scotthomeinspection.com/d...dit-Sample.pdf
    http://www.oxbowinspections.com/energyauditsample.pdf
    http://www.greenchipstocks.com/repor...ergy-audit/369
    http://deckerhomeservices.com/Sample...gy%20Audit.pdf

  8. #21
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,164
    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??
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  9. #22
    Join Date
    Apr 2001
    Location
    Over Here
    Posts
    1,105
    I have always wondered... We focus on R-50 or more for attic insulation, yet duct insulation is R-4 to R-6. The TD in ductwork is even greater when compared to the TD of the living space.

  10. #23
    Join Date
    Aug 2012
    Posts
    83
    After reading the following links the only plausable solution to the humidty issue was to add insulation and then wrap in a new vapor barrier like astro foil.

    http://hvac-talk.com/vbb/showthread....ensation/page2
    http://hvac-talk.com/vbb/showthread....and-Insulation
    http://hvac-talk.com/vbb/showthread....-vapor-barrier

    Thanks for those that responded. I've been educated.

    "R-19 is 6"..in attics where space is premium & compressing the insulation derates it..how is it going to work?? "

    I don't really follow your logic at all. Most attics I've been in our cramped, but adding 6" of extra insulation (12" total, ) is pretty easy , and space is hardly at a premium when the area is never used.

  11. #24
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,804
    You have to break the other vapor barrier before making another

  12. #25
    Join Date
    Aug 2012
    Posts
    83
    just slit it several times with a box cutter, pretty easy to do.

  13. #26
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,804
    Yea, just making sure you were aware of that.

Page 2 of 5 FirstFirst 12345 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event