Ridge Vent Effectivness

randy427July 18, 2007

I am considering putting in a whole-house fan. When adding up the square footage of existing attic ventillation, how much does 40 foot of ridge vent give me?



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I have a ridge vent. It works great for the winter ventilation but does not cut in the summer heat. I installed an attic gable fan last summer and it helped a lot.

    Bookmark   July 19, 2007 at 10:02AM
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Ridge vents are one part of a two part system. Installing just one part will not do the job. Ridge vents let out the super heated air. You need to install intake vents at the lower part of the roof to pull in the cooler outside air. Soffit vents would be a solution.
The third issue is to install the correct number of the vents for the size of the attic. You need so many sq inches of venting for every sq foot of attic flooring.
If you install a power attic fan you might have to increase the number of intake vents based on the size of the fan(which is sized based on the attics sq foot.)
On the fans box will be what you need in the way of vent requirements.
Each vent you buy will have the venting sq inches on it. This also goes for the ridge vent. Each linear foot will equal so many sq. inches.

    Bookmark   July 19, 2007 at 12:06PM
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This ridge vent has been in place for years, so there's no box to read. Any rule-of-thumb like 1 linear foot is 16 sq" of vent?

    Bookmark   July 19, 2007 at 5:39PM
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Brushworks Spectacular Finishes

Most ridge vents will provide approximately 18 square inches of net free area per foot.


    Bookmark   July 19, 2007 at 9:08PM
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Brushworks Spectacular Finishes

Just a reminder. Ridge vent is never to be used as an intake vent.


    Bookmark   July 19, 2007 at 9:10PM
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"This ridge vent has been in place for years, so there's no box to read"

"On the fans box will be what you need in the way of vent requirements."

Whether you have the paperwork is not important. As long as you can get a decent estimate of what you have and compare it to what you need to make the system work. Most of the time people slap stuff on the roof with no concept of the system involved. I'm speaking about homeowners and contractors, especially roofers who stick up a few tiny vents on a roof and call it a day. Guys who install attic fans without enough intake vents so the fan pulls conditioned air out of the house.
You just sit down with a pencil and paper before you start cutting holes.

    Bookmark   July 20, 2007 at 9:38AM
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I've owned 2 house in which I installed a whole house fan. With proper ventalation, they really work well.

So, when installing a whole house fan, the most effective way to exhaust the air is to use gable vents. Chances are your house will have gable vents already. You will probably need to increase their size.

Ridge vents and soffit vents will not be enough to make a whole house fan function properly. If you do not have gable vents, you will need to have them installed. Be advised that this installation will involve a structural change to your roof/ gable structure so you may want to contact a contractor.

Enjoy the journey.

eal51 in western CT

    Bookmark   July 21, 2007 at 9:53AM
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A contractor's input might be a good idea. Originally, our house had a gable vent at each end, and 3 soffit vents on one side of the house only. No vents in the garage!!! Ugh. When we installed our new roof last year, the contractor put in a ridge vent, and added several soffit vents, on both sides of the house, about every 10' or so.

We had to close up our gable vents or they'd serve as intake vents and suck in the snow in the winter. Previously, our ceiling would be warm to the touch, and our garage extremely hot in the summer. It's much better now with the ridge vent going across the entire house and garage. We decided not to get a whole house fan as we no longer needed it.

    Bookmark   July 22, 2007 at 1:58AM
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eal51 said:
"I've owned 2 house in which I installed a whole house fan."

What you're describing is an attic exhaust fan, not a whole house fan. A whole house fan intake areas are the doors and windows in your house. It's used to cool the house, not the attic. This is only effective when it's cooler outside then the house. An attic fan will be on a thrmostat located in the attic and go on when the temperature reaches 100-110 degrees in the attic. It will equalize the attic temps to the exterior temps.

    Bookmark   July 23, 2007 at 9:56AM
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I think eal51 was describing a whole house fan. I agree with him that is unlikely a ridge & soffit vent will provide enough area to properly vent the attic with a whole house fan running.
Enough gable venting could provide for the whole house fan exhaust, but would tend to short circuit the ridge/soffit vent.
BTW- A whole house fan exhausting through the attic does wonders to cool the attic. It's just not usefull when the A/C is running of course.

    Bookmark   July 24, 2007 at 12:46PM
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I have a recommendation for whole-house fans, and that is to go with the ones made by Triangle Engineering of Arkansas (made in the USA!).

These things move more air than any other brand. As an example: the 36" belt-drive model sold at Lowes & Home Depot moves 6,900 CFM on its highest speed. The 36" one that Triangle makes moves 10,600 CFM.

I just put one of these in last week and am so taken with it that I'm evangelizing for Triangle now.

These things are much higher quality than the other brands too -- these are made with very heavy-gauge solid welded steel (as opposed to the thin, flimsy metal - often aluminum - that other brands use). They use a very solid motor made by Emerson, the best of the top three motor-making companies (the other two being Fasco and A.O. Smith). They come pre-framed on a wood frame for installation, AND they have sponge-rubber noise-dampening material between the fan and the frame, so they are much quieter than the other brands. Also, Triangle holds a patent on an automatic belt-tensioning system these things use, so you don't have to worry about getting the tension right when you install the fan (or in the years thereafter as the belt loosens up).

Also, they come in more sizes than the other companies -- from 24" all the way up to 48" blade diameter (which moves a ridiculously whopping amount of air; no one else makes one that big).

They're sold online at Southern Tool amongst other places that ship nationwide, so they're available wherever you live.

Also, Triangle re-brands some of these as a private label for Dayton, which is the "store brand" of Grainger - so if you have a Grainger store near you (check your phone book or their website), you can buy one there. I will say this, though - Grainger/Dayton makes their own shutters, and those shutters are much better than the one Triangle makes. Triangle makes great fans, but crappy shutters. Luckily, they're sold separately -- so buy a Triangle fan and Dayton shutters; money can't buy better products.

They also re-brand some for a company out in San Francisco called "Fanman" (a/k/a "Delta Breeze").

A word to the wise -- these fans move a lot of air, so make sure to install at least the recommended minimum amount of attic exhaust space (gable vents, soffit vents, roof vents, some combination thereof, whatever works for you) - if you don't have enough, the fan will operate at reduced capacity, and there will be a backpressure which will cause the shutters to rattle when the fan is in operation (any time you hear whole-house fan shutters rattling, you know there isn't enough exhaust space). Oh, and one other thing -- only buy a belt-drive whole-house fan, don't EVER buy a direct-drive model...the direct-drive models are at least five times louder, they sound like standing on an airport runway next to an old prop plane getting ready to take off.

Several of the dedicated whole-house fan installing companies have chosen to use Triangle fans; that should tell you something. These companies want satisfied customers, so they use Triangle and only Triangle.

Refer to http://www.trianglefans.com/wholehouse.html for more info

Here is a link that might be useful: Triangle whole-house fans

    Bookmark   February 15, 2009 at 6:40AM
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The ventilation provided by eave and ridge vents is intended to allow moisture to escape the attic space. They will have only a modest effect on the temperature of the attic space because that heat build up is primarily from the hot roof sheathing radiating energy to the attic floor where the warm floor heats the air in the attic.

Adding more ventilation to your attic with a fan will remove hot air from the attic but it can also bring more moisture in from the outside in a humid climate. If you want to reduce the heat in your attic you should add insulation and/or a radiant barrier in the rafter bays in addition to what is already part of the attic floor assembly.

A whole house fan is for a different purpose altogether.

    Bookmark   February 15, 2009 at 10:34AM
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whole house fans are a waste IMO,running these fans will only suck the conditioned air from your living area making your frunace or AC/HP run harder and longer than necessary. Your best bet is to add insulation in your attic space to R-50 have the proper ventilation in the attic wither by soffit and ridge venting or gable venting along with ridge venting will be more than enough ventilation for the attic space. If you have any equipment in the attic space be sure your duct work is insulated properly and sealed good to prevent your return air taking in hot air from the attic and pushing it into the living space is essential. In fact if your attic space has blown in insulation and you do have duct work running thru the attic it is best to have those duct runs barrier in the blown in insulation to give the duct work the most insulating factor you can provide.

    Bookmark   February 16, 2009 at 4:57PM
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Huh? The whole idea of whole house fans is that you open the windows and cool (or warm) your house by drawing in outside air. You would never use them at the same time as your heating/cooling system - makes no sense.

My whole house fan is one of the best additions that I've made to my house. Turn it on at night in the summer and cool the whole house down - then close the windows during the day - hardly any need for air conditioning except for about seven days/year.

    Bookmark   February 17, 2009 at 9:31AM
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You don't need it to be cooler outside for a whole-house fan to be effective, although drier climates are better. The idea is the huge movement of air produces a cooling effect to the skin because of evaporation. I'm not sure what the fan is supposed to do in terms of exhaust but you don't want to just pressurise your roof space. I'm sure they have to be vented a particular way.

They certainly aren't used in conjunction with a/c, usually instead of, as Dennisgli said. Where I live in Kamloops, BC it would be ideal, because it's dryyyyyy here...and gets pretty hot, but I want to get a heat pump so I can heat the house with it most of the rest of the year.

    Bookmark   February 17, 2009 at 1:38PM
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I agree with dennisgli. I live in southern Cal and installed a ridge vent and fan last year. Theres good and bad ridge vents. Shop around. I had Lowes order it for me. When installed with a whole house fan they kick butt. You open the windows up and run a whole house fan at night when its cooler outside than inside. Then if you have decent insulation and Argon filled windows you only need the AC for an hour or so in the summer or maybe not at all. Saves bookoo bucks.Check out this link.

Here is a link that might be useful: Ridge vents

    Bookmark   February 18, 2009 at 11:59PM
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Dawger, after listening to my neighbour's a/c running constantly, even in the fall, I concluded they must have it set very cool. Right now, we don't have any a/c and want to get a heat pump, mostly for the heating - like you, I think we could do without much of the cooling (I lived in Australia for many years, so the dry heat of Kamloops BC is a walk in the park for me)

My question is, how did you regulate/restrict your a/c use? Just by turning it off, or did you set your thermostat high, or what? Just curious, because I'm thinking once you turn your a/c on, it seems in some ways you're committed to leaving it run unless you take some sort of steps...eg I hear it's best not to alter it too much during the day if you want a cool evening because it takes a while to catch up.

Since we are in a semi-alpine area with decent evening breezes, we open the house up as soon as we see the outside temp is cooler than inside, and close it in the am when it's warmer out. Like you, I don't intend to work the a/c too hard when we get it.

    Bookmark   February 20, 2009 at 2:27PM
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" Since we are in a semi-alpine area with decent evening breezes, we open the house up as soon as we see the outside temp is cooler than inside, and close it in the am when it's warmer out"

That's the ticket for us, 4500' in the sierra nevadas where it gets chilly even in the summer at night. Open up the house at night, close it down first thing in the morning, no a/c needed!

    Bookmark   February 20, 2009 at 7:03PM
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For a whole house fan, or what the Home Ventilating Institute (HVI) calls "a whole house comfort ventilator", you need a 1 square foot opening for every 300 cubic feet per minute (cfm) of airflow. So a 1000 cfm fan would require a 3.3 square foot (clear) opening. A 7000 cfm fan would require a 23.3 square foot opening! (You have to subtract the area blocked by louvers, etc.) The net free area of most ridge vent products is pretty low, ranging from about 18 square inches per linear foot for the best to 7 square inches per linear foot for the worst. Ridge and soffit vents are really there to prevent ice dams, keeping the roof deck at an even temperature. They do very little for cooling the attic or eliminating moisture. It's a much better step to carefully seal all the holes in the attic plane and prevent the moisture from getting into the attic in the first place.

Here is a link that might be useful: Heyoka Solutions

    Bookmark   July 24, 2012 at 1:59PM
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Where I live, a whole house fan would be ideal, it's semi-arid but pretty hot in summer. Unfortunately I want to go for a heat pump as it'd take care of a lot of my heating needs in the fall/winter/spring, so a HH fan would be more or less superfluous.

    Bookmark   July 26, 2012 at 1:24AM
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