Results 1 to 7 of 7
  1. #1

    Question about plenum material

    Hi,
    I'm new here, and have a question about a construction material HVAC contractors in the area are wanting to use. I've got a new central air and evap. coil, and it's different height/width than the old unit, so the original sheetmetal plenum has to be replaced. I'm trying to avoid ductboard, but finding local HVAC folks that do sheetmetal fab. is tough, everyone wants to use ductboard or flexible duct, and a few want to use this stuff.

    My question is: has anyone here ever used foil-faced polyisocyanurate foam insulating board to make a plenum? It's foil-faced on one side like ductboard, but it's foam in the center. The heat ratings that I've seen on the stuff in home centers sounds more than adequate for a heating system, and shouldn't be a problem with a/c.

    Is it becoming common for this to be used?

    Is it safe? (RE: flammability, toxic gases, etc)

    I may have the plenum part incorrect; its the area from the top of the evap. coil housing that connects to the main sheetmetal duct system that runs throughout the house. I think some folks call it a trunk line as well?

  2. #2
    Join Date
    Nov 2007
    Location
    Texas
    Posts
    425
    LIMITATIONS OF USE
    Check applicable building codes. As with all foam plastics, this product will burn. Johns Manville AP sheathing products must be protected from open flame and kept dry at all times. Do not leave exposed. AP sheathing requires an interior finish of a minimum 1/2" (13 mm) gypsum board or equivalent 15-minute fire barrier.
    AP sheathing is a non-structural product; use acceptable corner bracing. Check local building code for specific requirements.


    Can't get wet, is flammable, and emits toxic gases when burned (not a good idea for you air distribution system). Never heard of this being used, but I would bet someone on here has seen it done...by a hack installer.

  3. #3
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    It is polyurethane foam, one of the "better living thru chemistry" products. At first glance I was concerned about its combustion products during a fire, but looking up the safety data sheets on the material, it probably is barely more toxic than wood would be.

    I wonder what is the reason to avoid getting wet?

    Thanks -- Pstu

  4. #4
    Join Date
    Nov 2007
    Location
    Texas
    Posts
    425
    I just posted from what I read on the U.S. Department of Energy:
    Ensuring Fire Protection

    Foam insulation is relatively hard to ignite, but when it is ignited, it burns readily and emits a dense smoke containing many toxic gases. The combustion characteristics of foam insulation products vary with the combustion temperatures, chemical formulation, and available air.

    Because of these characteristics, foams used for construction require a covering as a fire barrier. One half-inch thick (1.27 cm) gypsum wallboard is one of the most common fire barriers. Some building codes, however, do not require an additional fire barrier for certain metal-faced, laminated foam products. Check with your local building code/fire officials and insurers for specific information on what is permitted in your area.


    I am not motivated by issues of money or emotion, but rather on giving advice on the safety of said materials. If you wold like to perform a test on your own home to find the safe levels of burning foam board, please feel free and post results. I myself have a 2 year old daughter and don't need to worry if the money I save could kill her due to an attic fire spreading smoke through the duct system of my home.

  5. #5
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Wherever you live there are sheet metal compaies around. So your HVAC contractor doesn't do sheet metal. That's not a show stopper. Have him take the dimensions needed and have the plenum (you're using the correct terminology) custom built. Then the contractor can just install it.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  6. #6
    Join Date
    Jul 2010
    Location
    DFW -> Texas
    Posts
    446
    Quote Originally Posted by hiah View Post
    Hi,
    I'm new here, and have a question about a construction material HVAC contractors in the area are wanting to use. I've got a new central air and evap. coil, and it's different height/width than the old unit, so the original sheetmetal plenum has to be replaced. I'm trying to avoid ductboard, but finding local HVAC folks that do sheetmetal fab. is tough, everyone wants to use ductboard or flexible duct, and a few want to use this stuff.

    My question is: has anyone here ever used foil-faced polyisocyanurate foam insulating board to make a plenum? It's foil-faced on one side like ductboard, but it's foam in the center. The heat ratings that I've seen on the stuff in home centers sounds more than adequate for a heating system, and shouldn't be a problem with a/c.

    Is it becoming common for this to be used?

    Is it safe? (RE: flammability, toxic gases, etc)

    I may have the plenum part incorrect; its the area from the top of the evap. coil housing that connects to the main sheetmetal duct system that runs throughout the house. I think some folks call it a trunk line as well?
    I like sheet metal due to animals and duct board is easily damaged by people in attics.

    Most manufactures have pre-made sheet metal plenums.

    I do use flex duct unless there are animals to worry about. Sheet metal ducts are expensive.

  7. #7
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190
    There is a foam product that Knauf used to market called KoolDuct that fits your description. It is now called by it's manufacturers name of KingSpan of Great Britian.
    This product is UL181 there is another product out there whose name escapes me, but no matter it is NOT Ul 181 and therefore DOES NOT meet the code,

    I am sory to hear you don't care for ductboard. When fabed correctly and sealed with UL181 tape, it can give you the same results at 1/3 the cost. Too bad you have too many who don't know how to fab and install properly
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

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