Page 1 of 2 12 LastLast
Results 1 to 13 of 15
  1. #1

    Confused Fiberglass insulation inside plenum

    Hello:

    A contractor is installing a new high efficiency furnace for me soon to replace an older unit. The air conditioner is newer and the contractor plans to install the new furnace and leave the existing plenum and AC coils in place. He will clean the AC coils. The old plenum has what appears to be fiberglass insulation glued to the inside of the sheet metal. I don't think the contractor noticed the old fiberglass.

    Question: Is this old fiberglass a inside the plenum a bad idea and should I ask him to remove it? What is good practice? Should the inside of the plenum be insulated, part of it is not where a previous contractor installed the new AC coils and a humidifier.

    Your opinions will be appreciated, Gene

  2. #2
    Join Date
    Dec 2006
    Location
    Vancouver, B.C.
    Posts
    41
    Insulation installed on the inside of the duct is for acoustical attenuation only. The only stuff that i know of that is used is black in color with a fabric backing to it. The fabric back stops the insulation fibers from blowing away in the air stream. There is a bit of a trade off with this stuff. It reduces noise but it often seems that bits and pieces break away from the duct or get lifted in the air stream after time. Most of the time you'll never notice that this has happened until replace the duct for whatever reason. There are rare occurrences that it will come loose and block the airway. That being said though, it's a product that i wouldn't hesitate to install in my own home.

    If your talking about the foil backed thermal insulation like what you would find wrapped around the outside of the duct or the stuff like in your walls than i would have that removed. If you post a picture than we can better identify what type and see the condition that this insulation is in.
    Quickly, I must hurry, for there go my people and I am their leader!

  3. #3
    Join Date
    Feb 2009
    Location
    U.S.A
    Posts
    34
    it would be better to remove it if you can. Then wrap the out side with insul. Last chance of any airborn particles.

  4. #4
    Join Date
    Oct 2008
    Location
    SoCal
    Posts
    27
    Remove and insulate on the outside if the existing insulation is falling apart as was said. If it's still good sometimes the edges can be sealed with duct sealant to prevent the air from peeling it off into the airstream.

  5. #5
    Thanks for the advice. I will ask the contractor to remove it since it is plain old ordinary fiberglass and particles of it likely enter the airstream. Gene

  6. #6
    Join Date
    Oct 2006
    Location
    The Beach
    Posts
    747

    Unhappy Duct Liner

    There is some good duct liner out there now. Ask the contractor to remove the old fiber glass liner, clean up the pleum and replace it with good material. It is a black material that comes in what ever thickness he want to use.
    We should not be breathing fiber glass.
    Blue Fox

  7. #7
    Join Date
    Feb 2004
    Location
    SW Florida
    Posts
    1,264
    Quote Originally Posted by lentz View Post
    There is some good duct liner out there now. Ask the contractor to remove the old fiber glass liner, clean up the pleum and replace it with good material. It is a black material that comes in what ever thickness he want to use.
    We should not be breathing fiber glass.
    The best duct liner is no duct liner

  8. #8
    Join Date
    Dec 2006
    Location
    Vancouver, B.C.
    Posts
    41
    There is some good duct liner out there now. Ask the contractor to remove the old fiber glass liner, clean up the pleum and replace it with good material. It is a black material that comes in what ever thickness he want to use.
    We should not be breathing fiber glass.
    Quote Originally Posted by zzonko View Post
    The best duct liner is no duct liner
    I think what you will find is that every technician will have their own opinion on this subject. To insulate or not to insulate... Its one hell of a question! there's people who will insulate the whole system to reduce noise as much as possible, some people will only insulate the return side so the filter will catch any fibers broken loose, then their are those who don't like to install it at all. Its application specific and in your situation it simply comes down to your personal preference.
    Quickly, I must hurry, for there go my people and I am their leader!

  9. #9
    Join Date
    Feb 2004
    Location
    SW Florida
    Posts
    1,264
    Quote Originally Posted by thatguy View Post
    I think what you will find is that every technician will have their own opinion on this subject. To insulate or not to insulate... Its one hell of a question! there's people who will insulate the whole system to reduce noise as much as possible, some people will only insulate the return side so the filter will catch any fibers broken loose, then their are those who don't like to install it at all. Its application specific and in your situation it simply comes down to your personal preference.

    Its not an opinion. Duct liner is banned in all hospitals and most schools. It is banned for a particular reason. If you are trying to keep down mechanical noise, isolate the duct system with a canvass connection on one end and flex duct at the end of your take-offs. No matter what you do with internal lining there will always be fiberglass in your spaghetti.

  10. #10
    Thanks thatguy and zzonko. The contractor talked to me today and said he normally uses the black material you mentioned. He said he would remove the loose yellow fiberglass that is in my plenum and put in the black stuff. If the old insulation is hard to get out he says he will replace the plenum, either way it will be clean. Then I plan to have the duct work cleaned. I never thought I would be excited about getting a new furnace but I am really looking forward to a lower heating bill, a quite blower, and cleaner air. Thanks everyone, Gene

  11. #11
    Join Date
    Dec 2006
    Location
    Vancouver, B.C.
    Posts
    41
    Quote Originally Posted by zzonko View Post
    Its not an opinion. Duct liner is banned in all hospitals and most schools. It is banned for a particular reason. If you are trying to keep down mechanical noise, isolate the duct system with a canvass connection on one end and flex duct at the end of your take-offs. No matter what you do with internal lining there will always be fiberglass in your spaghetti.
    zzonko:
    I agree that certain applications don't use insulation therefor it is definably application specific, But, it is not banned in residential along with many other areas in the industry.

    I know hospitals are very particular about their air quality and for good reason, but, Unless you are preforming open heart surgery in your kitchen than it is an still an option. as strongly as you may feel against it, it is an option, it has its positives and negatives and it is not against code.



    Gene1:
    I think you may have opened up a can of worms
    Quickly, I must hurry, for there go my people and I am their leader!

  12. #12
    Hi,

    I'm in the process of collecting bids for 2 new ac/furnace units.

    All the quotes to date have included new metal plenums, with insulation on the inside. I never gave it a second thought. I presently have metal plenums with the insulation on the outside with my Yorks.

    Well this morning, I received another quote, and this time the contractor said I should keep my existing plenums, to save on costs, and he went on to explain how insulation on the inside can get moldy and catch dust post the filter and that they are not used in hospitals.

    To be fair, its a small company and they had to charge me considerably extra for the plenums (additional 15%), whereas the bigger companies include it as part of the turnkey bid.

    Exactly what insulation material is used on the inside of the plenum (fiberglass)? Just worried that it will distribute fiberglass.

    My units are in the attic and it gets 100+ in the summer. Am I just being paranoid for no good reason ?

    Thanks
    Chris

  13. #13
    Join Date
    Feb 2004
    Location
    SW Florida
    Posts
    1,264
    Quote Originally Posted by crisscross66 View Post
    Hi,

    I'm in the process of collecting bids for 2 new ac/furnace units.

    All the quotes to date have included new metal plenums, with insulation on the inside. I never gave it a second thought. I presently have metal plenums with the insulation on the outside with my Yorks.

    Well this morning, I received another quote, and this time the contractor said I should keep my existing plenums, to save on costs, and he went on to explain how insulation on the inside can get moldy and catch dust post the filter and that they are not used in hospitals.

    To be fair, its a small company and they had to charge me considerably extra for the plenums (additional 15%), whereas the bigger companies include it as part of the turnkey bid.

    Exactly what insulation material is used on the inside of the plenum (fiberglass)? Just worried that it will distribute fiberglass.

    My units are in the attic and it gets 100+ in the summer. Am I just being paranoid for no good reason ?

    Thanks
    Chris
    Well I will tell you that in addition to being banned in hospitals and schools (fiberglass liner) it is increasingly being shunned by project specifiers on commercial installations. It is not banned in resi work that I know of, but for that you would have to check with your local building authority. It is not only the fiberglass that gets into the airstream but the V.O.C. chemicals that are used to press and hold it tight. And if gets wet it will grow mold and hold dust. Outside of that its great stuff.

Page 1 of 2 12 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