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I have a single story house with an unfinished attic. The attic has a bunch of blown cellulose insulation up there. The thermal camera shows that the ceiling areas on exterior walls are conducting heat in. Any way to improve or mitigate this?

Also, the attic temperature on really hot days is around 135F. I've read some places that it's a problem and other places say it isn't. I have two gable vents and soffits, but no fans. I've read that fans often do more harm than good so I've been hesitant to install one or more.

What brought this up is I feel my AC is not able to keep my house cool and my power bill has been a bit outrageous. The AC unit overall is 7 years old. The cold air coming out of the vents is 18-20 degrees cooler than the air going back in the return. The static pressure is also .5 in h20 between the return and the supply. I keep up on filter maintenance and I don't think there's anything wrong with my unit. I should also note that the air handler is also up in the attic.

I'm looking for any pro-tips/suggestions to address the heat transfer along the ceilings of exterior walls and potentially some info on the hot attic.

Pictures: https://imgur.com/a/3aAQgx2 (attached same pictures twice because one of each shows the scale).

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  • Make sure the soffits are open and maybe think of ridge vents. If adding more insulation at the ends can use baffers to keep the soffits open.
    – crip659
    Commented Aug 15, 2023 at 14:44
  • as far as i know, my soffits are not the open/close style, they're one long continuous vent that runs the span of both sides of my roof.
    – Alex
    Commented Aug 15, 2023 at 16:49
  • Do you have baffles like this? atticexperts.com/wp-content/uploads/2021/01/vent-baffles.png They allow the air to come in the eaves/soffits and rise up to the attic, particularly with blown insulation, which tends to block eave vents without baffles.
    – Huesmann
    Commented Aug 16, 2023 at 12:47
  • My baffles aren't that fancy, they're just what looks to be cardboard stapled on to the beams to prevent blown insulation from falling down in to the soffit area.
    – Alex
    Commented Aug 16, 2023 at 14:40

2 Answers 2

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If the attic is 135 F and the highest interior spot temperature you can find is 80 F, then I'd say the insulation is working perfectly.

18 F temperature drop over your A/C coil doesn't sound right though. It sounds like there hasn't been any professional maintenance on this system in a long time. Have a pro come out for a routine service call.

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    It would seem that a thermostatically-controlled attic fan might be a useful addition. Even if the outside air is 120F it would help to exchange it for the 135F in the attic.
    – Jon Custer
    Commented Aug 15, 2023 at 14:51
  • That's not "18 F temperature drop over your A/C coil", it is between supply and return vents - e.g., might be set thermostat for 75, cool air coming out at 57, returning at 77, which sounds reasonable to me. The supply air temperature is not the same as the coil temperature. Commented Aug 15, 2023 at 15:52
  • Yea as another commenter replied, the temperature differential is between supply and return vents. I just wasn't sure if the interior ceiling being that much hotter was "normal" but it sounds like it might be and there isn't much for me to improve on.
    – Alex
    Commented Aug 15, 2023 at 16:51
  • 18 F temp delta is right on the spot
    – Traveler
    Commented Aug 15, 2023 at 18:01
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A 10 degree difference from the edge to the rest of the roof doesn't seem too bad, considering there should be a bit less insulation on the edges to allow for air flow at the soffits.

You want to ensure that any insulation up there doesn't block the intake at the soffits so you move enough of the hot air out and reduce the overall temperature of the attic.

There are a lot of incentives on right now in Canada and the US for energy improvements, so you could add more insulation, but if you were to go that route I would ensure you installed some soffit baffles first to make sure you have enough air flow for the soffits and then add more on the edges, but overall it doesn't seem too bad.

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  • Thank you! My soffits do have baffles and insulation doesn't block/interfere with air flow. So sounds like I'm in good shape and about as good as it's gonna get. Thanks again!
    – Alex
    Commented Aug 16, 2023 at 14:40

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