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astroboy 06-22-2008 04:56 PM

Efficacy of roof attic fans?
I'm considering putting in a couple of powered attic vents. Despite a lot of anecdotal evidence, I'm not sure how much difference they'll make to the temperature inside the house. We live in a high desert environment (Carson City, NV); the single-floor house is 11 years old, and is quite well insulated. It has 2x6 exterior walls which are full of fiberglass, and there is about a foot of blown insulation in the attic. What's giving me pause is some measurements I've made with a handheld infrared thermometer. Readings taken at 3 PM and 8 PM show only one-to-two degree difference between interior walls, exterior walls, and the ceiling. Will one or more attic fans make a significant difference in the indoor temperature?


mrkool 06-22-2008 05:23 PM

Hello Jeff,

Here in Middle Tenn, it's a very good idea, I'm installing 2 or 4 next week and probably 10 next month, I've proven to myself, they can relieve up to 12,000 Btu-H of heat gain for some houses
and unmeasurable damage to the roof and especially if you store items in the attic. After last years 105 degree Summer, it's a cheap savings all the way around.
Since I own an HVAC company, I'm using a fan and bracket from a 5 ton condensing unit to cool my attic, because it's 220 volt, it draws less power, but it's stronger.
If you have gables with real louvers, not the plastic/vinyl preforated triangle, get a measurement and get the biggest fan you can use, then cover up any roof vents that are
close by so you can get a cross breeze from the far end, if no gable(s), then roof mount is the next best thing.


pweller 06-24-2008 10:34 PM

You need to look at the temperature difference between your attic and the outside. An attic fan is only going to equalize these two temperatures. If you only have a 10 degree difference, I suspect it won't do you much good. Probaby, if your house is fairly new, it has adequate passive ventilation.

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