Power Fan with box vents or ridge vent okay?


I’m getting different views from manufacturer reps on this one. Shocker…actually not. I know if you install ridge vent you need to close the box vents and close the gable vent. I also know to make sure there is plenty of soffit ventilation. Some of these goofy homes I can’t ridge vent for various reasons so I’m stuck with the box vents and sometimes no soffit venting or gable ventilation. “See moron builder 101.” So I’ve been suggesting installing a power fan about 2ft below the box vents or ridge vent. I often do this on hip roofs where there is minimal ridge area. Another contractor told my customer I was nuts. SOOOO…am I nuts? And what’s everyones opinion on the new solar fans? I was curious about that too. Thanks!


Ya dont say…

I completely disagree.


Good job.

Install 2 right next to each other instead of just one due to its much weaker power.
Yes, it is a little expensive at first.
Pays later.

I don’t think any one knows about their longevity yet.


The advice to delete the box vents is correct…given the following:

If you install ridge vent in conjunction with the appropriate soffit vent, you will have the proper airflow.

Any box vents near the ridge will disrupt the flow… now they will act as an INTAKE, so the flow will be very short… from the box vent to the ridge. Yes, the soffits and box vents will still provide some ventilation, but the full linear flow of air from bottom to top will be disrupted. Typically, I wouldnt recommend using both box and ridge vent together…use one or the other.

Gable vents on an average rambler style aren’t as disturbing to the airflow, as they are more near the peak. Given their size, however, if a home already has gable vents, there isnt a big need to go ridge vent at that point. Everything you need is already in place.

Powered fans, especially thermostatically controlled, including solar fans, are a great way to complement your ridgevent and move more air, especially in hip-roof areas where you have very minimal ridge.


Thanks for confirming I’m not nuts.


In addition to what roof-lover said, check these links for more information and related video.

roofingcontractorreview.com/Roof … -Myth.html

roofingcontractorreview.com/Hip- … nting.html


I don’t disagree with the video. Problem is that Certainteed disagrees with the video. These guys drive me nuts. They say if I do not close the gable vents I’ll void the warranty. They say the gable vents will create a vortex of swirling air, thus rendering the ridgevent ineffective. I think it’s a load of crap, but who am I to argue with the reps? My real question has become lost though. I was asking if putting a power fan just below the box vents or ridgevent was okay. I’ve done it a thousand times, but I had another contractor tell my customer I was crazy. That was the real question I was trying to get answered.


If you’ve done it a thousand times, you can easily answer your own question with a few experiments. Go up on some of those old roofs when the fan is running, or go into the attic and force it on first. Then go over to the box vents with some strips of paper and see if they are being sucked into the vent. If so, close off the vent from inside the attic and you’re done.

You want the full air flow of the fan to draw in the coolest air possible and exhaust the hottest air possible. If you can’t use ridge vent, then pull off two of those box vents, open up the holes, and put power fans there instead. If you know what you’re doing, wire them so that they operate from a single thermostatic relay, and put the extra thermostat in the “spare parts you will likely need later” box. Just don’t put the fans downslope - they do the most good when they are as close to the peak (and as near the center of the house) as possible.

If you don’t believe in doing it that way, argue your point with the manufacturers, but don’t let your choice void the customer’s warranty.

If you really want to do it up right, harken back a couple of generations and get them to put a whole-house fan in the ceiling downstairs, install double-hung windows so they can lower the upper sashes, put sufficient static venting on to accomodate the CFM of the WH fan and let 'er rip. And then ask them for the unused air conditioner so you can sell it on Ebay.

Just for the record, I actually do have a degree in physics.


Good points by neville.

A power fan in place of two box/turtle vents would provide about the same static ventilation.

If the soffits are sized to the power fan, enough nfva, then I don’t see a problem.

And you could ask the manufactures reps to produce the test results that show this “swirling vortex” effect. :smiley: