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My mom lives in a converted barn

Caren V. | Posted in General Questions on

Hi. I hope someone can help me. My mom lives in a converted barn. The air conditioner and oil burner are in the basement which in on the ground floor in the back and underground in the front. It’s on a slope. She lives upstairs. In the summer, the central…

The basement is on a slab. I don’t know how much insulation is in the walls or attic. Oh, and the attic is only in the center of the apt. The lower part of the ceiling is a cathedral ceiling. I think the whole apt is about 800 square feet, if that helps. Thanks again!

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  1. GBA Editor
    Martin Holladay | | #1

    It looks like part of your post got cut off.

    Can you please tell use what your question is?

  2. Caren V. | | #2

    Whoops! Here's what's MIA: In the summer, the central AC overheats and shuts down. It's about 40 in the basement and almost 90 upstairs. There is no air exchange between floors. I know we need to insulate the ductwork, but should we also cut registers into the apt floor and install a whole house fan to bring the cold air up? Just want to see what's best before we hire a contractor. Thanks!

  3. GBA Editor
    Martin Holladay | | #3

    I'm not sure what you mean by "the central AC overheats and shuts down." Perhaps you intended to write something like, "The air conditioner shuts off when the downstairs thermostat is satisfied, even though the top floor is still hot."

    It's hard to know from your description, but I'm guessing that this house needs:

    1. Air sealing work to limit infiltration and exfiltration.

    2. Insulation improvements.

    3. A Manual J calculation to determine room-by-room heating loads and cooling loads. (For more information on this issue, see Who Can Perform My Load Calculations?)

    4. A properly designed duct system, which is now lacking, to deliver cool air to the upper floor.

  4. Expert Member
    Dana Dorsett | | #4

    A temp of 40F in the basement when it's 90F upstairs is a condition that only happens in or near perma-frost zones. Where are you?

    Exchanging cold air from the basement with 90F air from the upper floors won't maintain the temperature difference for long. It's essentially using the basement slab as the heat exchanger to the colder subsoil, but there isn't enough surface area to keep up with higher BTU rate. The better strategy would be to lower the load on the upstairs, and/or improve the air flow balance with the central air, or install a separate cooling system for that zone, say a mini-split heat pump right-sized for the zone's cooling load.

    If the same ducts are used for both heating & cooling, they are almost never properly sized for both cooling & heating loads across multiple floors. What works fine during the heating season will almost always leave the upstairs under-cooled during the cooling season, due to the higher solar gains from both the roof and the higher exposure of upper floor windows.

  5. GBA Editor
    Martin Holladay | | #5

    I suspect that Caren comes from a family where exaggeration is used as a form of emphasis. It's a rhetorical device, I imagine.

    I don't think we're supposed to understand her sentence -- "It's about 40 in the basement and almost 90 upstairs" -- the way we might understand testimony from a scientist providing data for a published paper.

  6. Expert Member
    Dana Dorsett | | #6

    Martin- I get that, but used that as a hook to try to figure out what sort of climate we're dealing with here. :-)

    A whole house fan can make sense in some climates, not so much in others.

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