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  1. #1
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,475

    Spray Foaming Ductwork

    Seems the foam insulation is starting to get popular around here. Have two full installs, back to back, where they are foaming the walls and ceiling. On top of the sheet rock, not the underside of the roof.

    These will be my first installs with this sort of insulation. The load calcs came out drastically smaller than what Im used to seeing. I will trust them but must say im a bit worried.

    To my question....The bigger install is two story, about 6k sq feet. The upstairs unit will be in the attic space. The insulator is trying to get the HO to spray foam that ductwork, which I really have no issue with but thought Id run it by you guys and see what your opinions and experience are on doing this?

    Also. They used engineered trusses between floors which is always a PITA. Ive always insulated my pipe between floors. Feel stupid for asking but is it necessary?

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,062
    Spray foam on ducts must closed cell foam not open cell. Open cell will allow moisture to penetrate and condense on the cold surface.
    Fresh air ventilation? Its a must. You need a fresh air change in 4-5 hours. Supplemental dehumidification also needed in green grass climates. A whole house ventilating dehumidifier is a good choice for most green grass climates. Ultra-Aire is a sponsor.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  3. #3
    Join Date
    Nov 2011
    Location
    Phoenix,AZ
    Posts
    149
    Why are they spraying foam on the sheet rock that defeats most of the benefit

    If they were spraying on the underside of the roof all the duct work will be in conditioned space

  4. #4
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    4,653
    Quote Originally Posted by KevinAdv View Post
    Why are they spraying foam on the sheet rock that defeats most of the benefit

    If they were spraying on the underside of the roof all the duct work will be in conditioned space
    Most of the benefit being?

    If you spray the roof sheathing, then you have to heat and cool the space in the attic. Whats worse, having a super-insulated duct system in a well ventilated attic, or having to heat and cool your entire attic?

    Seems to me like starting your envelope at the drywall is a good place.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  5. #5
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,585
    You said the heat load was really low, This is just an example of how well it works, I was running some hydronic lines in a area with a drop ceiling, I was soldiering the pipe 6" away form the foam and I was literally dripping sweat after 6 joints is got so damn hot up there , it really impressed me.

  6. #6
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    5,658
    Spray foaming the roof deck is definitely the way to go over foaming the attic floor. The ah/furnace cabinet will be inside conditioned space as will the duct work. The attic will stay within a few degrees of the living space. You have to bring in fresh air in a tight home like this so I hope you are putting the V back in HAC.

  7. #7
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,475
    Im not the insulator so cant tell you why they are doing the ceiling instead of the roof decking. Yes I will be bringing in fresh air.

  8. #8
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,826
    Quote Originally Posted by hvacvegas View Post
    Most of the benefit being?

    If you spray the roof sheathing, then you have to heat and cool the space in the attic. Whats worse, having a super-insulated duct system in a well ventilated attic, or having to heat and cool your entire attic?

    Seems to me like starting your envelope at the drywall is a good place.
    All of the homes we've done with geo-thermal have been high efficiency homes and all have had the closed cell foam insulation installed under the roof. This provides both basic insulation as well as a thermal barrier against the sun load, as well as sealing the attic. Naturally forced, controlled ventilation is a must but forced ventilation that can be controlled is far superior to natural ventilation that runs willy-nilly and decreases as it gets warmer outdoors due to less chimney effect. In winter, those attics get quite warm just from convection air rising from the living space. In summer, with well sealed and insulated ducts, they stay warm but not hot. Thus, the actual load on the 2nd floor zone is decreased as opposed to a 135 attic space.
    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!

  9. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,062
    Quote Originally Posted by ar_hvac_man View Post
    Im not the insulator so cant tell you why they are doing the ceiling instead of the roof decking. Yes I will be bringing in fresh air.
    How about expanding on "I will bring in fresh air"? The devil is in the detail!
    Anxious to here about it. How much and how will you control it?
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  10. #10
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by hvacvegas View Post
    Most of the benefit being?

    If you spray the roof sheathing, then you have to heat and cool the space in the attic. Whats worse, having a super-insulated duct system in a well ventilated attic, or having to heat and cool your entire attic?

    Seems to me like starting your envelope at the drywall is a good place.
    Yes, if your equipment is inside the home, but if its' in the attic, huge advantage. Foaming the roof deck vs the floor, the surface area doesn't increase dramatically unless you have a steep roof pitch. But then you're gaining conditionsed storage space and a potential bounus room in the future. You're never going to seal the ductwork 100%. So all leaks in a vented attic are the same runing supply and return ducts outdoors, except hte air is even hotter. All that supply ductwork has conditioned air in it, so your delta T is even greater, and it's only isnulated to R8-10. That's a lot of surface area. Six 25'x 8" supply and return ducts are about 52 square feet Plus the air handler and plenums, you are probably at 60-70 square feet for a typical system.

  11. #11
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,475
    Quote Originally Posted by teddy bear View Post
    How about expanding on "I will bring in fresh air"? The devil is in the detail!
    Anxious to here about it. How much and how will you control it?
    Regards TB
    Im still chewing on that. The first job is a two stage gas pack. The HO has family who owns a supply house who sells nordyne. I was hired to install it and run the ductwork. I normally back away from that but it will keep my guys busy for 3 or 4 days. My thoughts on the gas pack was a motorized 0-35% fresh air damper that is energized when the blower is.

    The big house will have fresh air piped into the platforms for the downstairs units and im still unsure about the upstairs unit and not sure how it will be controlled on either level. Ill see what the supply house offers and go from there.

    Open to suggestions for both homes

  12. #12
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,062
    Quote Originally Posted by ar_hvac_man View Post
    Im still chewing on that. The first job is a two stage gas pack. The HO has family who owns a supply house who sells nordyne. I was hired to install it and run the ductwork. I normally back away from that but it will keep my guys busy for 3 or 4 days. My thoughts on the gas pack was a motorized 0-35% fresh air damper that is energized when the blower is.

    The big house will have fresh air piped into the platforms for the downstairs units and im still unsure about the upstairs unit and not sure how it will be controlled on either level. Ill see what the supply house offers and go from there.

    Open to suggestions for both homes
    Any well built home needs controlled fresh filtered air when it is occupied. ASHRAE suggest an air change in 4-5 hours. This is about 100 cfm per 3,000 sqft. It is tied to occupancy, not a heating/cooling cycle. A whole house ventilating dehumidifier is an ideal device to blend filtered fresh air into the home via the cooling ducts. The dehu will also maintain <50%RH when the a/c does not have a high cooling load. I suggest the Ultra-Aire line of wh hs dehu which are available to wholesalers throughout US.
    Check it out. They are also sponsors of this site.
    Regardless fresh air and supplemental humidity control are a must for health and comfort.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  13. #13
    Join Date
    Jan 2001
    Posts
    6,652
    Quote Originally Posted by ar_hvac_man View Post
    Seems the foam insulation is starting to get popular around here. Have two full installs, back to back, where they are foaming the walls and ceiling. On top of the sheet rock, not the underside of the roof.

    These will be my first installs with this sort of insulation. The load calcs came out drastically smaller than what Im used to seeing. I will trust them but must say im a bit worried.

    To my question....The bigger install is two story, about 6k sq feet. The upstairs unit will be in the attic space. The insulator is trying to get the HO to spray foam that ductwork, which I really have no issue with but thought Id run it by you guys and see what your opinions and experience are on doing this?

    Also. They used engineered trusses between floors which is always a PITA. Ive always insulated my pipe between floors. Feel stupid for asking but is it necessary?
    I knew a guy once that had a commercial building that he bought and he had the whole thing spray foamed. He opted for spraying the underside of the roof...........lol

    That roof had several leaks in it and for the three or four years that I knew about......they never found or fixed the leaks.

    I told him his only option would be to "cool seal" or otherwise coat the entire roof but he opted for buckets and pools of water on the floor instead.

    Dont ever coat the underside of the roof with that mess.........lol
    As Seen On You Tube (usually under someone elses name)

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