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Old 03-24-2012, 09:25 PM   #1
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Gable vent fans - intake vs exhaust


I live in a house built around 1950, so no soffit vents and no current ridge vent. I would like to provide some more attic ventilation. The walk out attic has 3 gable vents, 2 on one side on each side of the chimney and another gable vent on the opposite side of the house. If I put a gable vent fan in the lone gable vent side, would the opposite side with the two gable vents provide enough intake? Would this help to cool the attic?

Thanks for the input.

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Old 03-24-2012, 09:44 PM   #2
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Gable vent fans - intake vs exhaust


Without soffit vents all those vents are doing little good.
Any power vent would just suck air in the gable vents. The whole idea is get rid of the moist air in the attic, not suck more in.
Any chance at some point of getting some pictures of the soffit area to figure out how to add some vents?
With a ridge vent and soffit vents all those other vents could be blocked up and the attic would be cooler and dryer.

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Old 03-24-2012, 10:20 PM   #3
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Gable vent fans - intake vs exhaust


Gable vents work fine if you have a power attic fan that is well placed and on a thermostat. Every house I have lived in for the past 55 years has had gable vents and either no other vent at all, or a powered fan, and contrary to what some people will tell you your house will not rot to the ground or burst into flames. Amazing how houses even existed before ridge vents :D

FYI, heat should not be your primary concern, but rather moisture buildup. If your worry is that the heat is lowering the efficiency of your conditioned space, then the answer to that is more insulation and air sealing between the conditioned space and the attic.

You can add a power attic fan. Put it in a spot where it will draw air as equally as possible from your gable vents to give you the best air evacuation.
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Old 03-25-2012, 02:16 PM   #4
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Gable vent fans - intake vs exhaust


+1

Gable end vents have worked great for years.

You could argue that they worked a number of years ago when we weren't generating as much moisture in the homes, however, proper air sealing and isolation of the living space from the attic space will largely contain and prevent the migration of most of the moisture in the home.

I would also add that a combination thermostat and humidistat might be preferable on the attic fan.
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Old 03-25-2012, 02:47 PM   #5
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Gable vent fans - intake vs exhaust


I have an old house with only 2 end gable vents. I had a solar attic fan installed a year ago and it seems to be doing a good job. Whenever I poke my head up there, I feel some air current.
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Old 03-25-2012, 03:02 PM   #6
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If I put a gable vent fan in the lone gable vent side, would the opposite side with the two gable vents provide enough intake?
The powered vent fan should indicate how much cfm it will draw, or how much free intake space is needed from the opposite gable vents.
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Old 03-26-2012, 03:01 PM   #7
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I have an old house with only 2 end gable vents. I had a solar attic fan installed a year ago and it seems to be doing a good job. Whenever I poke my head up there, I feel some air current.
of course you do, since you just opened up a source of venting (the attic access hatch). A better test is to get up there, close the attic hatch, and then see if you feel the air current. And if your attic hatch does not seal very well, then you are likely losing quite a bit of conditioned air out of the living space.
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Old 03-27-2012, 12:46 AM   #8
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Gable vent fans - intake vs exhaust


You're probably right. I think I have good intake ventilation though between my two gable vents and my solar attic fan. It wouldn't hurt to test it out with the attic hatch shut tight. Do you have much confidence in those hatch covers that are designed to fit over them?
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Old 03-27-2012, 11:33 AM   #9
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+1

I would also add that a combination thermostat and humidistat might be preferable on the attic fan.
What should the thermostat be set at to turn on the attic fan?
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Old 03-27-2012, 11:38 AM   #10
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Gable vent fans - intake vs exhaust


Probably 20-30 higher than maximum ambient temperatures.

Attic ventilation is not for attic cooling. It is for moisture removal.
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Old 03-27-2012, 11:43 PM   #11
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Originally Posted by rreynolds12 View Post
I live in a house built around 1950, so no soffit vents and no current ridge vent. I would like to provide some more attic ventilation. The walk out attic has 3 gable vents, 2 on one side on each side of the chimney and another gable vent on the opposite side of the house. If I put a gable vent fan in the lone gable vent side, would the opposite side with the two gable vents provide enough intake? Would this help to cool the attic?

Thanks for the input.
1. What is your location? Heating or cooling climate?

2. Is the attic air sealed? Insulated per minimum code for your area?

Primary reason of venting is to prevent ice dams by removing the heat and moisture coming from below: http://www.buildingscience.com/docum...on?full_view=1 Need the insulation, air-sealing first, the rest advice depends on climate.

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Old 03-28-2012, 07:49 AM   #12
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Gable vent fans - intake vs exhaust


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Originally Posted by joecaption View Post
Without soffit vents all those vents are doing little good.
Any power vent would just suck air in the gable vents. The whole idea is get rid of the moist air in the attic, not suck more in.
Any chance at some point of getting some pictures of the soffit area to figure out how to add some vents?
With a ridge vent and soffit vents all those other vents could be blocked up and the attic would be cooler and dryer.

Ahh, replacement air coming into the attic will be the same outside air whether it enters through gable vents or soffit vents. The problem with introducing a power vent into the mix is the chance it will depressurize the attic and pull more moisture laden and/or conditioned air into the attic from the living space. AIR SEAL, AIR SEAL, AIR SEAL.

Ridge vent/soffit vent is my system of choice, but is not always the best/most cost effective system for the situation. Properly sized, the OP's solution should work fine.
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Old 03-28-2012, 07:51 AM   #13
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Gable vent fans - intake vs exhaust


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Originally Posted by strategery View Post
You're probably right. I think I have good intake ventilation though between my two gable vents and my solar attic fan. It wouldn't hurt to test it out with the attic hatch shut tight. Do you have much confidence in those hatch covers that are designed to fit over them?
Never bought one, but have built a couple from rigid insulation board. Very DIY friendly project. Also look at any wire/pipe/vent penetrations through the ceiling.
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Old 03-28-2012, 03:06 PM   #14
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Gable vent fans - intake vs exhaust


That is a tricky question and depends who you ask. I recently went to a two hour seminar by Air Vent about this exact topic that was very informative. Their expert recommendation was to close off all your gable vents from the inside (board them up), then install adequate intake soffit vents and ridge vents that have equal exhaust and intake. Here is some information {hope it helps } Proper attic Ventilation


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Precision Construction

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Old 03-28-2012, 03:22 PM   #15
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Gable vent fans - intake vs exhaust


Of course they would say that. They don't sell ridge vent without saying that.

Gable end vents have worked for years.

Air sealing is first on the list.

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