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Combining an Attic Vent Fan with a Roof Ridge Vent
By: Danny Lipford 
Our contractor installed a ridge vent on our roof. We were still getting significant heat build up in the attic, so he then installed a solar roof fan that moves 500 CFM (cubic feet per minute). I noticed you said that these two systems should not be combined. Should we remove the solar vent fan? -Ron
Hi Ron,
Attics are vented using the natural circulation that occurs when hot air rises. Vents in the soffit beneath the eaves at the bottom of the attic draw in cool outside air while gable or ridge vents at the peak of the attic allow heated air to exit. In hot climates, a power vent fan is often mounted behind a gable vent or cut into the roof near the peak to assist this process by forcibly expelling additional hot air from the attic.
Combining an attic power vent fan with a ridge vent is usually not recommended because:
- It could reverse the natural flow of hot air out the ridge vent.
- If air is drawn in through the ridge vent while it’s raining, it might pull rainwater in with it, which could lead to leaking or mold in the attic.
While a power vent fan combined with a ridge vent can work against the natural flow of air through the attic, it will still exhaust more hot air than not having a fan at all, it’s just not the most efficient way to go about it.
Since your solar vent fan only moves 500 CFM (a third to half that of a typical hardwired attic vent fan), it probably won’t move enough air to reverse the action of the ridge vent. Also, since the fan is powered by the sun, it should turn off when the sky is overcast during a storm, which will keep it from drawing rain into the attic.
So, while it’s may not the most efficient way to cool an attic, in your case I would continue using the solar vent fan. You might want to check the attic occasionally when it’s raining to see if there is any water coming in the ridge vent.
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12 Comments on “Combining an Attic Vent Fan with a Roof Ridge Vent”
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September 4th, 2010 at 1:40 pm
what if you installed fans mounted upward next to the ridge vents forcing air from the soffit vents, would this cool off your attic saving on your ac from working so hard
September 21st, 2010 at 9:16 am
I was wondering if the same issues mentioned in the article apply when you mix ridge vent with other passive venting at the peak of the roofline? In my situation I believe I need more venting at the top of the attic but there is no more space to add ridge venting and I would rather not add a gable. If I add passive venting such as the whirly bird vents or similar do you still have the issue of pulling air/rain through the ridge vent?
Ben Erickson Says:September 27th, 2010 at 12:15 pm
Hi Cameron,
Since turbine vents don’t have much sucking power, I would think it would be okay to put them near the ridge, or you could add several of the smaller unpowered vents that are made to be installed on a roof. Good luck with your project!
February 27th, 2011 at 7:58 pm
My attic has soffit and ridge vents. I checked them and they seem to be done properly, but my attic still gets very hot. You said adding a roof fan isn’t very efficient with this system. Where could I put a fan to increase circulation and efficiency in my attic? Doug Commented earlier about installing a fan inside the attic pointing up at the ridge vent. Would this work?
June 12th, 2011 at 1:09 pm
We have a single story house, approx 2800 sq. ft. with ridge vents on a steep roof (12×12). Te air intake is thru holes in vinyl soffits
The attic temp gets up to 129 – 130 deg with the summer heat in Covington, LA, and our electric bills get to $400/month. We had an energy consultant suggest that we add 2 or three whirly birds near the top of the roof near the ridge vents.
I see from information that I found online that that we shouldn’t mix different types of exhaust vents since one type may pull from the other.
What do you suggest?
September 13th, 2011 at 6:38 am
I have an attic that has a square floor. I have perforated soffit vents extending around the entire perimeter of the floor. I have a powered attic fan controlled by a thermostat. Each side of the roof is sloped, so the sides of the roof meet at the top of the roof in a very short ridge vent about three feet long. It seems from what I have read that having both a powered fan and a ridge vent at the same time is taboo. However, in my case, since the ridge vent is so short (too short for adequate ventilation without a powered fan in my opinion), isn’t it wise to stick with both a powered fan and a ridge vent in my case when I replace my roof?
November 21st, 2011 at 10:49 pm
My husband and I just bought a brick home with vinyl tiny holes in the soffit area, these let no light at all into the attic. The home has a thermostat based electric fan mounted near a peak in the roof, but it also has 2 gable-end vents and ridge venting. I believe the previous owner recognized they had a problem, but never investigated the soffit. How do we fix it at this point? It appears to have been designed to be continuous, but someone either closed it all in with plywood or forgot to leave it open? Thanks for any input. We just want to make sure we get it right and stop all the moisture before it is a problem.
March 2nd, 2012 at 5:20 am
Check to make sure:
1.you can see daylight through your soffit vents,if not redo them, contiuous is better than other forms.
2.you have baffles in the attic to keep the insulation from blocking the bay.
3.how much ventilation do you need lxw divided by 1.5 is total, then divide by 2 so half is for soffitt and half for roof. ex. your house is 32×24=768 divided by1.5=5.12 then divide by 2 for equal parts soffitt and roof.the answer is 2.56. this figure you can multiply by 144 to get square inches.
4.if you have a ridge vent and if it is not effective (most brands arent, add old fashioned roof vents, the average on requires a hole with an 8 inch diameter.
5.stick to the formula for the roof as close as possible dont worry if you have to much soffit vent,especially if you have electric fans.
The other school of thought is to eliminate both soffit and roof vents alltogether and spray foam the attic ceiling and treat it like any other conditioned space of your house.
Ben Erickson Says:March 2nd, 2012 at 6:59 am
Hi Robert,
Thanks for the feedback on attic ventilation, good points!
May 3rd, 2012 at 12:44 pm
Danny: Our 2-story home with a walk-up attic recently had a new roof installed with the addition of a ridge vent. For air intake – there are absolutely no soffit vents, and only a few static vents placed low on the shady side of the roof. I’m concerned that we are still very short on cool intake air. The attic has two north facing dormers. I’m considering installing two solar powered gable fans – in the dormers, with the airflow reversed. The goal is to have the fans introduce the cool air from the north/shaded side of house – into the attic to cool & exhaust through ridge vents. Am I creating any headaches?
May 5th, 2012 at 2:47 pm
Hi….I live in Florida, have a hip roof with ridge vents and unobstructed soffits. On sunny summer days it still get unbearably hot up there, and is the reason I think my AC continues to run at night even though it’s cooler outside than my thermostat setting.
I’m not about to put any more holes in the roof (hurricanes), but I’ve considered putting a vent fan blowing upwards into the roof in the soffit. It seems to me it would bring cooler outside air into the roof area, and the increased pressure would force the warmer air up through the vents. Working off of a thermostat, set to 100 or so degrees, I wonder if such an arrangement would increase airflow up and out of the roof.
Any thoughts on the matter?
May 14th, 2012 at 1:11 pm
I’m with Mike McGee.
I’m in Florida and would like to take a gable fan and mount it on my off-ridge vent blowing up/out. I don’t have any gable ends, it’s all hip-roof design.
I’m looking for reasons why won’t this work.
Thanks