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Thread: Insulation INSIDE supply ductwork

  1. #1
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    Insulation INSIDE supply ductwork

    Hi there,

    I am having a central air system put into my home. I told the contractor he must insulated all supply ductwork. And he did. But I have a question. He insulated INSIDE the supply ducts. He glued a black 1/2 inch thick insulation inside of the ductwork. Is this normal?

    Please help as they are going to start hanging the duct work tommorrow and I want to know if it's safe.

  2. #2
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    duct insulation is safe and normal.

  3. #3
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    Thread Starter
    But INSIDE the ductwork? I've always seen duckwork insulated on the outside of the ducts with a wrap.

  4. #4
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    Insulation inside will not tear, quieter and will last longer than an outside wrap and it is more expensive because of the labor involved. First class I say.
    "I could have ended the war in a month. I could have made North Vietnam look like a mud puddle."

    "I have little interest in streamlining government or in making it more efficient, for I mean to reduce its size. I do not undertake to promote welfare, for I propose to extend freedom. My aim is not to pass laws, but to repeal them. It is not to inaugurate new programs, but to cancel old ones that do violence to the Constitution."
    Sen. Barry Goldwater

  5. #5
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    Interesting !!! I was waiting to hear someone say they were using Duct bd.

  6. #6
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    Depends on the climate area and where the ductwork is installed.

    Lined duct is not the best idea in a humid cooling dominated climate with the duct installed outside the conditioned space.
    1/2" insulation isn't much, and is against code in many areas. Around here we have to use R6 or R8, depending on the SEER rating of the equipment.

    I would never use lined duct in my area, but it gets a little hot and/or humid in my area, and 99% of our duct systems are located in attics.

    I'm also not a fan of fibrous materials in the air stream after the filter, but if it installed correctly, that shouldn't be a problem.

  7. #7
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    Quote Originally Posted by mark beiser View Post
    Depends on the climate area and where the ductwork is installed.

    Lined duct is not the best idea in a humid cooling dominated climate with the duct installed outside the conditioned space.
    1/2" insulation isn't much, and is against code in many areas. Around here we have to use R6 or R8, depending on the SEER rating of the equipment.

    I would never use lined duct in my area, but it gets a little hot and/or humid in my area, and 99% of our duct systems are located in attics.

    I'm also not a fan of fibrous materials in the air stream after the filter, but if it installed correctly, that shouldn't be a problem.
    I am truly amazed at these last two posts. The op did not describe db in anyway. This is a metal duct (expensive not cheap like duct board) and the insulation is a black heavy foam like material (forgot the name haven't used it for years because expensive to install). You clue it to the inside of the duct section by section as you install the metal duct.

    It is slow going and the most expensive way to install duct in a home. I still got a roll of the stuff left over from the last job I did about 12 years ago where it was used inside a metal trunk line running on the basement ceiling in a house. The trunk line was sized used static regain method to get equal velocities through the line as it ran down the long basement in the big house. Reducing in size from a 24 by 12 to a 14 by 12 at the in. 8" Flex duct was used in the branch runs running off the trunk line. Geez give me a break. I guess it isn't used much and most of you all have never seen it.
    "I could have ended the war in a month. I could have made North Vietnam look like a mud puddle."

    "I have little interest in streamlining government or in making it more efficient, for I mean to reduce its size. I do not undertake to promote welfare, for I propose to extend freedom. My aim is not to pass laws, but to repeal them. It is not to inaugurate new programs, but to cancel old ones that do violence to the Constitution."
    Sen. Barry Goldwater

  8. #8
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    The OP never said what kind of insulation it is. Just that its black and 1/2" and glued.

    So it could be foam, or fibrous.
    Either way, it is used in many areas. And he is doing what you said you wanted.
    If you wanted the duct wrapped, you should have said you want it wrapped.
    Its too late now, unless you want to pay him extra to make new duct and wrap it.
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  9. #9
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    Quote Originally Posted by beenthere View Post
    The OP never said what kind of insulation it is. Just that its black and 1/2" and glued.

    So it could be foam, or fibrous.
    Either way, it is used in many areas. And he is doing what you said you wanted.
    If you wanted the duct wrapped, you should have said you want it wrapped.
    Its too late now, unless you want to pay him extra to make new duct and wrap it.
    I may be mistaken but I have never heard of "glued" fibrous insulation. Inside glued foam will last forever without the worry of tape coming unglued like wrapped insulation and the duct being exposed and thus loss of insulation. As long as the rating of the insulation meets or exceeds the code you are getting a first class job. Why would you want it wrapped? I would go for the better quality not a wrapped insulated duct where the insulation will deteriorate over time.
    "I could have ended the war in a month. I could have made North Vietnam look like a mud puddle."

    "I have little interest in streamlining government or in making it more efficient, for I mean to reduce its size. I do not undertake to promote welfare, for I propose to extend freedom. My aim is not to pass laws, but to repeal them. It is not to inaugurate new programs, but to cancel old ones that do violence to the Constitution."
    Sen. Barry Goldwater

  10. #10
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    insulating the inside of the ductwork is no problem just takes longer. as long as the installer sizes the duct correctly, compensating for the 1/2" on each side of the duct there should be know probs. the only prob i have seen in when the supply plenum on a gas furnace is insulated on the inside with a humidifier, sometimes the humidifier causes mold in the supply plenum. but just central air shouldn't be a prob.

  11. #11
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    Quote Originally Posted by glennac View Post
    I may be mistaken but I have never heard of "glued" fibrous insulation. Inside glued foam will last forever without the worry of tape coming unglued like wrapped insulation and the duct being exposed and thus loss of insulation. As long as the rating of the insulation meets or exceeds the code you are getting a first class job. Why would you want it wrapped? I would go for the better quality not a wrapped insulated duct where the insulation will deteriorate over time.
    It was very common here. it was (and still is ) glued and pinned.

    Do a search for fibrous glass duct liner.
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  12. #12
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    Wrapping sheet metal can save both the customer and company money.
    Its easier to move air through unlined sheet metal then to move it against the higher friction of a liner ( liners increase the size of the duct, increasing cost ). Many companies don't know the friction rate of the liner they use. They just increase the size of their duct by the total thinckness of the liner ( a rule of thumb ). And then end up with a higher TESP then they designed for. (different liners have different roughness factors)

    Not saying you used rules of thumb when you lined your duct, or that you didn't know what the increased friction rate of the liner you used was.
    But some companies don't.
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  13. #13
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    Have used both foam and fibrous.. also wrap on the outside most of time.. others only if specified

  14. #14
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    Quote Originally Posted by beenthere View Post
    It was very common here. it was (and still is ) glued and pinned.

    Do a search for fibrous glass duct liner.
    Nice to know about glued fibrous duct liner but I will say that it had to be foam insulation because the op did say "black" insulation and for what it is worth I did take into consideration of course the 1/2 insulation for sizing the duct. My velocities were below 800 at all times in the trunk line and the duct work was sized to keep the static pressure the same throughout the trunk line so you would have close to equal distribution in the branch lines even without using dampers.
    "I could have ended the war in a month. I could have made North Vietnam look like a mud puddle."

    "I have little interest in streamlining government or in making it more efficient, for I mean to reduce its size. I do not undertake to promote welfare, for I propose to extend freedom. My aim is not to pass laws, but to repeal them. It is not to inaugurate new programs, but to cancel old ones that do violence to the Constitution."
    Sen. Barry Goldwater

  15. #15
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    Thats why I didn't imply that you didn't allow for it.
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  16. #16
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    we use sound lined duct here in FL al the time rarely have any problems unless liner isnt glued and pinned would not allow for glued only liner

  17. #17
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    Quote Originally Posted by glennac View Post
    I may be mistaken but I have never heard of "glued" fibrous insulation. Inside glued foam will last forever without the worry of tape coming unglued like wrapped insulation and the duct being exposed and thus loss of insulation. As long as the rating of the insulation meets or exceeds the code you are getting a first class job. Why would you want it wrapped? I would go for the better quality not a wrapped insulated duct where the insulation will deteriorate over time.
    I've never seen this foam duct liner, only the fibrous stuff.

  18. #18
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    if it is an ACOUSTIC (sound deader) insulation it is BEST on the INSIDE of the duct.

    if is an THERMAL insulation it is BEST on the OUTSIDE of the duct.

  19. #19
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    *

    Quote Originally Posted by mark beiser View Post
    I'm also not a fan of fibrous materials in the air stream after the filter, but if it installed correctly, that shouldn't be a problem.
    even if it was installed correctly, i still would not have it!



    .

  20. #20
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    I just posted a video on YouTube. At the end of it are pictures of the 'insulated ductwork' . Please look at it and let me know your opinions. Thanks for all the comments.


    http://www.youtube.com/watch?v=2TbXffMcA-E

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