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Power Attic Ventilators – Bad Idea

Power attic ventilators, once thought to be a great idea, are now deemed to be a bad idea. That goes for the “now popular” solar power attic ventilators. You know the ones, using the sun to make the electricity that powers the fan? However, using the sun to power your attic ventilators is only marginally better than using the electric models.

Why are we talking about power attic ventilators just as winter is coming on? There’s a very good reason why now. It’s time to unplug those power attic ventilators now during the cooler weather.

Power Attic Ventilators – The Debate

power attic ventilators may actually cost you more than they claim to save youPower attic ventilators will probably keep your attic cooler during the hot summer months, and that means you’ll have less conductive heat transfer across your ceiling. The problem is that a significant portion of the cooling in your attic will be provided by your air conditioner. So, you spend money to buy the fan, to run the fan if it’s not solar, and then your air conditioning bill goes up, too.

You ask, “How can the A/C bill go up? Isn’t it supposed to pull that blazing hot air from the attic and send it outside, replacing it with much cooler outdoor air that gets pulled in through the soffit and gable vents? In marketing theory, yes. Building science shows a different result, however.

What really happens is that when that power attic ventilator runs, it’s going to pull air from wherever it can find it. Since air takes the path of least resistance, some of it will most likely be coming from the conditioned space in your home. So basically what you’re doing is air conditioning your attic. The longer the fan runs, the more conditioned air it pulls into the attic from every little nook and cranny the air can find to get into the attic.

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If you have a perfectly air-sealed ceiling, you’re not going to have this problem, of course. The reality, however, is that very few ceilings are leak-free. Since air needs only a pressure difference and a pathway to move, and your ceiling probably has plenty of pathways, it’s best not to enhance any pressure differences that will increase air movement into or out of your home.

Another major problem is that passively ventilated attics bring in large amounts of moisture laden air into the attics during the evening and morning hours when relative humidity is often high. This can lead to sweating air conditioning ducts and air handlers with associated insulation and even ceiling damage.

Our best advice: Don’t install power attic ventilators. If you have one or more of them installed already, disable them so they never run.

If you’re tempted to buy one because it’s solar-powered and won’t make your electric bill go up, go back and read what we just said. These things probably won’t save you any money. Even if they’re solar, they’ll still suck the conditioned air out of your house and make your bill higher, not lower.

If your roofing shingles are near the end of their life expectancy, consider the color of shingles you replace them with. Tests comparing white and black shingles have shown that shingle color makes a greater difference in peak shingle temperature than the presence of one or more power attic ventilators. Black shingles tend to be almost 25 degrees hotter than peak temperatures for white shingles.

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There are many studies that have been done on power attic ventilators and their effect on your power bill, attic, roof, and comfort level of your home. This article is not intended to cover all aspects of these findings, but if you have more questions or would like a consultation to discuss these findings, please don’t hesitate to give us a call. If you’re considering whether to install power attic ventilators or not, by all means, call us. Brown and Reaves Services, Inc. 843-497-9867. And don’t forget to Like us on Facebook and grab your 20% off coupon on our next service call.

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