Home Improvement Expert Danny Lipford

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Combining an Attic Vent Fan with a Roof Ridge Vent

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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.

Danny

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27 Comments on “Combining an Attic Vent Fan with a Roof Ridge Vent”

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  1. doug Says:
    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

  2. cameron Says:
    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?

  3. Official Comment:

    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!

  4. Zerry Says:
    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?

  5. Mack Deloney Says:
    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?

  6. Mike Leonardo Says:
    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?

  7. Jennifer Huckins-Todd Says:
    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.

  8. robert Says:
    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.

  9. Official Comment:

    Ben Erickson Says:
    March 2nd, 2012 at 6:59 am

    Hi Robert,
    Thanks for the feedback on attic ventilation, good points!

  10. Jeff Says:
    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?

  11. Mike McGee Says:
    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?

  12. Eric Says:
    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

  13. Les Vyhnalek Says:
    June 28th, 2012 at 6:13 pm

    I have a theory that if I add a fan to the ceiling of my attached garage (drawing air from around the garage door and glass block window vent – blowing up into the attic) it may help draw more air from the soffit vents. This may only work on the South side of our attic where most of the sun hits the roof. Thoughts?

  14. Larry Cooper Says:
    July 24th, 2012 at 8:51 am

    I have a large home with a second story. The roof has ridge vents and soffit vents. i want to install a powered vent system to pull the cooler air from under the soffits but I do not want to pull the hotter air in from the ridge vents. Is there a sheet metal duct like system that can be installed in my attic to mount the exhaust fans in so that they will blow air out of the ridge vents and only suck cooler air from the soffit vents?

  15. Ted Bucci Says:
    July 25th, 2012 at 6:29 am

    I have a 1950 built house. Sometime after that a family room 15×12 was added. 1950 insulation and only a gable vent.
    Cement slab under addition and there are no registers in this room to bring in heat or ac. What they have is a gas heater thru the side wall of this brick addition. This is a home that I just purchased–its summertime and I am getting ready to move in. Problem I have been working in this room painting, it is unbelievably hot and the attic from inside has no access—is not available from the existing house. I need to cool my attic first of all –no ridge vent and can I install say ridge vent or wind powered turbines from the outside only? No access to this small attic from inside. Old type ceiling and I dont want to tear it down.
    What suggestions to cool this attic?

  16. Jeff Says:
    July 25th, 2012 at 3:19 pm

    Larry Cooper – I installed a fan to blow into my attic. The goal is to have the fans introduce the cool air from the outside of house – into the attic to cool & exhaust through ridge vents.
    See my 05/03/2012 post above.

  17. alec Says:
    July 26th, 2012 at 9:19 pm

    I am interested in adding a second attic fan because my attic really gets hot. The contractor suggested sealing up 15 feet of ridge vent above each of the 2 attic fans. He says the reason for doing this is so the attic fans don’t draw hot air from the ridge vents. Does this make sense?

  18. Dave Says:
    November 20th, 2012 at 3:53 pm

    I have a similar issue with a very warm attic after having ridge vents installed when I replaced my shingles. Unfortunately, I did not measure the temperature with the old vented roof, but with the ridge vents the temperature as measured by an Acurite outdoor thermometer in the attic has gone as high as 155 degrees in the summer. Not sure if I trust the thermometer but it is pretty hot.

    I tried leaving the access door to the attic open to see if more input air would help – no difference at all. Tried mounting a 20″ box fan blowing air into an intake vent and maybe 5 degree cooler at best and maybe cools off sooner at night.

    I’m currently thinking of mounting an intake fan on one side of the house and an output fan on the onther.

    I really wish I’d measured the temp before the new roof, but I didn’t. Still as others are reporting my attic is hotter than I would like and I have ridge vents.

    Are some brands of ridge vents better than others?

  19. shawn Says:
    January 7th, 2013 at 8:11 am

    Hi there I have four ridge vents running across my second story. I was thinking about putting a powered exhaust fan in the gable.Do I need to put two or one and another non powered vent at other gable? Or should I just stay away since I read it can suck in rain through roof vents thx

  20. Dave Says:
    January 7th, 2013 at 11:10 am

    Everything I’ve read has indicated to not add separate out take vents when we have ridge vents. Still, I’m not very happy with my attic getting up to 155 on hot summer days.

    I’ve receive 1,000 sq ft of ventilated reflective foil that I plan to lay across the top of the insulation in the attic. This will not lower the temperature in the attic in the summer, but I can’t bring myself to put the foil right under the rafters.

    The people that seem to think the attic temperature is not a problem seem to be mostly the people that sell shingles.

    I may “bite the bullet” and put a gable in take fan at one end and a gable out take fan at the others.

    It is common to find posts by others with ridge vents that wish their attic temperature was lower. What I don’t know is if the attic temperature was lower, before switching to ridge vents.

  21. Seth Says:
    February 13th, 2013 at 11:00 am

    I live in an 1872 sq. ft. colonial in New Hampshire. The home is 3 years old and just recently I had a neighbor (who has the same size home tell me he has mold in his attic. I checked mine and sure enough just like my neighbor I have mold growing on the north side of my roof… We have soffit/ridge vents. I’ve had 5 more neighbors (all with the same house look and sure enough they all have the same problem??? Could it be that the ridgevent is not allowing enough air flow and I need to install one that allow more air flow? One of my neighbors added 4 more inches of blown in insulation after sealing all possible points of humid air entry including bathroom vent fans, smoke detectors, etc. and that did nothing to help….any ideas? Thank you!

  22. Denver Dave Says:
    February 13th, 2013 at 12:37 pm

    I started monitoring my attic temperature after installing ridge vents with my new roof and on hot summer days, gets up to 155. Unfortunately, didn’t measure the temperature before installing the ridge vents. Have enough attic floor insulation, does not seem to heat up the house, but still would like it to be cooler in the attic. I first tried leaving the attic access open thinking not enough intake air – no benefit. Then tried mounting a 20 inch box fan on the outside of the intake vents blowing air in – maybe 5 degree benefit and very slight faster cooling at night. I’ve purchased 1,000 sq ft of attic perforated foil that I plan to lay over the floor insulation, but haven’t installed yet. Shouldn’t change the actual attic temperature or maybe make it higher in the summer (might keep heat from going into the house). What we really need is someone to compare traditional venting with ridge vents to see if ridge vents really do leave the attic hotter or if it is just the people with ridge vents are monitoring the temperature.

  23. Melanie L. Says:
    February 25th, 2013 at 11:01 am

    Thank you for your website, it has been very helpful!
    We have an 11 year old home that was built with gable and ridge vents in conjunction with the sofits. About 5 yrs ago my husband installed a electric attic vent fan because our 2nd floor gets extremely hot in the summer. A couple of days ago after going into the attic we noticed mold growing on the trusses. Is this do the electric vent fan? Can it just be unplugged, or do we have to seal it up somehow? If yes, what would be that best way to do that? Thanks so much

  24. Jose Says:
    July 21st, 2014 at 9:17 pm

    I do not notice soffits on my house and am about to have a new roof put in, with ridge vents. I currently have 2 attic fans and the roofer suggested I remove them and seal the holes. Should I keep the attic fans since there are no soffits?

    Can soffits be added in order to make the ridge vents more effective? For what else can I check in order to make sure ridge vents work?

    Roof is a lot of money and I just want to make sure that I get the most comfort and protection from the new roof.

    Thank you all for the information.

  25. Jeff W Says:
    July 22nd, 2014 at 10:02 am

    Roof Replacement – Roof as insulator. Two years ago, I had a complete roof tear down and replacement. 1 layer of cedar shingles, and 3 layers of composite shingles were removed. After 2 summers with the new roof, I am amazed to learn how much insulating value the old 1-cedar and 3-composite layers offered, compared to the new plywood base and 1-layer composite. makes complete sense. 4 roofing layers vs 1.
    Don’t forget to take this into account if you are performing a complete roof teardown.

  26. Mike McGee Says:
    July 22nd, 2014 at 10:39 am

    ….not much experience with roofs, but it seems to me if you kept one fan and screened the other hole, you could exhaust the hot air under your roof, without drawing air from inside your house.

  27. Jeff W Says:
    July 22nd, 2014 at 11:01 am

    Ridge Vents are designed to permit hot air to rise to the highest point of the roof (ridge), and exit through the ridge vent. Basic physics would say that for the hot air to escape, need some method of allowing cooler air in to replace it.

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