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Ben H

Powered Roof Vent

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Saw one the other day, and it got me thinking how I rarely see any. Maybe one in a hundred homes around here have them.

I'm curious if it's a regional thing, building cost thing, or they just don't live up to what they claim thing.

Do you guys see them often? What is your opinion of them (when they actually work?

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About 1/3 to perhaps 1/2 of houses in my area have them. I don't think the cooling effects of powered vents justifies the impact they have on the electric bill.

Marc

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I see them often. Many do not last long. The motors burn out and lock up. They often have open splices/improper wiring.

I don't like them because of that and they are often installed with other upper ventilation that prevents them from operating as intended.

I prefer the continuous ridge and soffit vents.

Many folks in the south will disagree with me on the power vents.

I say if you plan to install them that in many cases you will need more than one, let them be your only upper ventilation, and get the ones with thermostats AND humidistats so it will also work when needed in the cooler months.

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I have one in my townhouse attic. The 4/12 comp roof covers 400sq ft attic that had only 4 4x12 soffit vents along one eave only and a single 12x12 vent in the upper third. The attic was reaching 160 degrees in summer, and the ceiling, under 8 inches insulation, was radiating a considerable amount of heat into the building at night. Not having any control over roofing or vents, I waited until the roof was being recovered and installed a new thermostatic power vent the day before. I'm now saving quite a bit on AC costs, much more than I spend on electricity for the fan. True, I have to monitor the fan and replace the motor every few years, but it's still a small price to pay.

It's a case by case basis whether a power roof vent will save power/money in the long run. I would much rather have installed a ridge vent, but sometimes that's not possible.

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Back in the day before ridge vent became common, I recommended people replace the motor with a permanently lubricated version. Granger has motors with the same frame. At that time a turbine was my choice over a power vent.

If you read the installation instructions that come with the power vents, the manufacturer directs the owner to oil the motor once a year.

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My house has gable vents and a power vent (1957 split level). There are no soffits and I decided that a power vent in the center of the upper rear roof was a better solution for me than a ridge vent. The power vent runs during the day for 2-3 months a year. The central A/C does not have to fight as much heat radiating down from the ceilings. The attic is much cooler on hot days and the house is more comfortable than before I had the fan installed.

All of the new houses we design have soffits and ridge vents. No power vents are installed in the new houses.

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One of these cookie-cutter design, build-on-your-lot companies in this area uses them on every model. House has to be tight, tho, as I have heard that on retro-fits or rehabs of older dwellings the power vent sucks conditioned air out of the living space.

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Saw one the other day, and it got me thinking how I rarely see any. Maybe one in a hundred homes around here have them.

I'm curious if it's a regional thing, building cost thing, or they just don't live up to what they claim thing.

Do you guys see them often? What is your opinion of them (when they actually work?

My opinion is they should never be installed unless there is absolutely no other option to ventilate an attic. I have installed them in the past, but no more after seeing literally hundreds of burned-out / locked-up motors.

They will not survive more than a couple of seasons around here since it is a flawed design. Trying to use an air cooled motor for continuous duty in an air stream that is 110-150 degrees just does not work.

Add to the reliability concerns the cost of energy to run the things and the fact that you are using interior air sucked through every hole in the ceiling to cool the attic and they become less and less attractive. Maybe, just maybe, if I was in an area that air conditioning was not required and the unit only ran a few weeks every year, I might consider... Nah, there are better methods![;)]

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I normally talk my clients out of keeping power fans in the attic as they tend to create hot spots and may pull hot air back in under the right conditions. I believe that the shingle manufactures (at least Certainteed) will void shingle warranties in many cases if the home has ridge and soffit venting AND a power fan.

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Here are some links to building science documents that describe power attic ventilators as a bad idea.

http://www.homeenergy.org/archive/hem.d ... 51103.html

http://tinyurl.com/m7nrq

http://tinyurl.com/66qq8jv

http://www.energystar.gov/index.cfm?c=d ... entilation

I've seen several attics with a PAV that had terrible moisture problems, not to mention the problem of not saving any energy during the summer.

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