Another attic ventilation issue

Discussion in 'Roofing and Siding' started by Toadfish, Sep 5, 2019.

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  1. Sep 5, 2019 #1

    Toadfish

    Toadfish

    Toadfish

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    We had a new HVAC unit installed and during the hot Georgia summers the attic will get up to 116F where the AC unit is installed. The second floor below the unit will get up to 76F. The thermostat is set for 72F. Sq.ft of the attic is about 1300-1500
    It has ridge vents, soffit vents and probably 10 or so roof vents. The HVAC guys have come out numerous times to check my system and cannot find any issues with the unit. It's has 10Kmore BTU's and 10K more CFM than my old unit and it did the same thing.
    They feel it's the extreme temps in my attic that are causing this issue.
    I installed a power gable vent and it has helped little.
    I talked to the vent manufacturer and they feel the power vent is pulling hot air from the ridge and roof vents.

    What do I do?
     
  2. Sep 5, 2019 #2

    oldognewtrick

    oldognewtrick

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    Mixing different kinds of exhaust ventilation is never a good idea. It's counterproductive. The ridge vent turns the 10 or so vents into intake vents, this short cycles the ability to intake at the eaves and exhaust at the ridge.
     
  3. Sep 5, 2019 #3

    Toadfish

    Toadfish

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    I agree. So what do I do? The existing vent system never functioned correctly. Do I add more vents? Or do I cover the existing roof vents and go with the power vent? Can I cover the existing roof vents with out causing other issues?
     
  4. Sep 5, 2019 #4

    nealtw

    nealtw

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    The heat in the attic sounds normal, how much insulation do you have in the cieling?
     
  5. Sep 5, 2019 #5

    oldognewtrick

    oldognewtrick

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    I'd remove the box vents. Or make them nonfunctional. Take a piece of rigid insulation and fill in the holes from the back sides or cover them with heavy plastic and duct tape. The power vent will draw air in from the ridge vent. I would discontinue use of it.

    As Neal said, heat of 110-115 or higher is common in attics. I'd look at insulation and make sure your a/c duct joints are not leaking.
     
  6. Sep 5, 2019 #6

    Toadfish

    Toadfish

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    I have R30 but some areas could use some more which I'll be adding after the AC issue is resolved. R38 which should cover most of the flexible duct work helping with heat gain.

    The HVAC guy's said the delta T was not in the range in which they would like. It's close but could be better.
    They attribute that to the attic being to hot. Basically the AC unit being in an oven.
    I rented a thermal camera and didn't see any hot spots on the ceiling below. Ceiling temps ranged from 72-75. Register temps were in the 65ish range.

    The HVAC company has checked the unit and originally thought it was the expansion valve. The coil was replaced along with the expansion valve with the same results.

    Yesterday at 7 PM I taped over some of the roof vents and blocked some of the ridge vents to see if it improves. Using smoke it was pulling more air and attic temps stated to drop but by then the sun was going down.
    It'll be in the 90's today and sunny so it'll be a good test.

    Since installing the power vent it looks like its taking the attic longer to heat up. It was reaching 75F + at the thermostat by 1-2 PM before the install.
    Yesterday at 2 PM it was 72 by 4PM it was 74 with 93 outdoor temps 75 at 5 PM

    "I'd remove the box vents. Or make them nonfunctional. Take a piece of rigid insulation and fill in the holes from the back sides or cover them with heavy plastic and duct tape. The power vent will draw air in from the ridge vent. I would discontinue use of it. "Discontinue use of what? Box vents?"

    As Neal said, heat of 110-115 or higher is common in attics. I'd look at insulation and make sure your a/c duct joints are not leaking."

    No duct's leaking verified by thermal camera. The power vent manufacturer suggested blocking the ridge vents also but some of which aren't reachable. :(

    Should I be blocking the roof vents and just leave the ridge vents open?
     
  7. Sep 5, 2019 #7

    oldognewtrick

    oldognewtrick

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    Are the soffit vents covered with insulation? Can you see daylight at the eaves when the attic light is off?
     
  8. Sep 5, 2019 #8

    Toadfish

    Toadfish

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    No and there are rafter baffles in place.
     
  9. Sep 5, 2019 #9

    Toadfish

    Toadfish

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    Update
    95F and sunny today. Thermostat is staying at 72 all day. :)
    Think I'll block off the roof vents and leave the ridge vents alone and see what happens.
    Wifey just checked the attic temperature 112-116.

    Insulation is next going to blow in R38+
     
  10. Sep 16, 2019 at 5:58 PM #10

    Toadfish

    Toadfish

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    So I added 12 more 5" diameter soffit vents, removed all vent blocks I installed. Didn't help at all. Still getting up to 75F. Blew in about 10+" of cellulose insulation on Saturday. Sunday Temps were in the low 90's and all is good. :) Today is supposed to be a bit hotter but I'm confident this problem is fixed. Got about R40 in the attic floor now. :)
    Left the power vent at 120F and it'll come on if needed.
     
    nealtw likes this.

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