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Community and Q&A

Destratifying Attic Space

stolzberg | Posted in General Questions on

We’re remodeling a house in Zone 5 (Northwest Massachusetts) and bringing the attic into the conditioned space.  It will be a single large space, approximately 40′ long and 20′ wide with ceiling about 16′ high at the ridge descending to 3′ knee walls on either side. We removed old slate roof, covered board sheathing with Grace Ice & Water as air barrier, then 7″ polyiso, plywood sheathing, and metal roof.  Inside we’ll also be putting batt insulation in 6″ rafter bays. We’re installing a minisplit on one of the gable walls (Mitsubishi MSZ-FS09NA indoor unit, MUZ-FS09NA outdoor unit). 

I’m wondering what is best way to ensure heating and cooling is distributed throughout the room, especially with such a tall ceiling.  I’ve read about a number of options, which include:

1. Ceiling fan in middle of room that can be reversed to either push hot air down or pull cool air up.  My concern with this is distracting shadows from can lights above it.

2. Bladeless fan in middle of room to circulate air.  I’ve read these are more efficient and better for destratification.

3. Horizontal blower: hang some sort of fan from the ceiling or mount on gable wall to push air across the room and hopefully circulate top to bottom.

4. Exhaust fan or duct fan that pulls hot air from the ridge and releases it near the floor.  I’ve heard of this being done between an attic and lower floors, but never within a single room.

Am I overthinking this?  Will the minisplit by itself be enough or does it make sense to add something to destratify the air within this space?

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Replies

  1. DC_Contrarian | | #1

    My experience is that if air leakage is controlled heat distribution is very even. You may not need anything.

  2. Expert Member
    BILL WICHERS | | #2

    I would use a ceiling fan if you actually notice any issues, but DC is right -- it's not always much, if any, of a problem. The easy way to "have it both ways" here would be to prewire a few ceiling boxes for potential ceiling fan use. If you end up not needing the fans, no big deal, but if you find that you do, all the wiring is already there so you're fan install will be easy. Remember to wire the boxes with 3 conductor + ground cable, so that you can control lights and the fan motor seperately. This would likely be a 14/3 WG cable.

    Note that you'd want at least two ceiling fans for a space this long, with the fans "half centered" on the space (which means in the center of each half of the space lengthwise). One fan is not going to give you even airflow over a space that long.

    Bill

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