Attic Fan

[SkunkedAgain]

It's time for me to finally install an attic fan. I've got decent airflow through the soffit vents and up through the roof vents, but my house has zero shade in the afternoon summer sun. It cooks that roof, heats up the house, and makes me have to run the A/C more than I care to do.

Here is my apparent problem. Looking online I seem to only find vertical-mounted fans meant to work on a gable vent, or roof-mounted fans that are built into a new roof vent. Don't they sell anything that I can mount underneath an existing roof vent? I don't mind ripping out an existing roof vent to install a new one with a fan, but it seems unnecessary. Then again, maybe my thought of just bolting a fan on the underside of an existing roof vent isn't efficient. Thoughts?

[K_Josh87]

i do not know of any such fans that do the task you are looking to complete...

[c0untryf1sh3r]

Heres a link to a fan that can be mounted up under a pre-existing vent, might take some creativity but it would work.

Pre-existing vent fan

Or this one from Northern Tool might work as well. Can be mounted vertically or horizontally, just needs to be hard-wired into the system. Dont know how big your attic is but I imagine 1600CFM would be enough.

http://www.northerntool.com/shop/tools/product_200461071_200461071

[chad austin]

I wouldn't do it, you will end up venting only the top 1/3 of your roof. Airflow will take the path of least resistance, the air that will be exhausted through the vent with the fan will be pulled from the vents next to it with no fan on them and you will create more issues for your self down the road. If you want a fan in the attic, put a fan on ALL of the vents that will all turn on at the same time, forcing a true soffit to roof vent exchange.

I see this all the time where a house will have gable vents, static vents and a turbine. The air has no path or direction in which it should flow. By putting a fan on each vent you create the path and truly exchange the air in the attic.

[crothmeier]

+1 what Chad Said. Too many and different kinds of vents can work against each other.

[CAMAN]

+2 to what Chad says!

Each and every roof vent needs a fan, otherwise the path of least resistance with be mostly through the other roof vents and not the soffit vents.

[SkunkedAgain]

Hmmm, I guess that I never considered that one would need to buy 6 new fans for all of the roof vent openings. Thanks for the advice. It'll probably sound like a prop plane on take-off

[CAMAN]

Here is exactly what you are looking for..

PDF

They are called roof vent booster fans.

[K_Josh87]

what they hay, +3 on chads advice...

[Tom7227]

I don't know beans about how many to put up but it sure doesn't make sense to me to put one up without some sort of automatic control on it. The Tjerlinde product didn't seem to have anything like that. At least 25 years ago a friend put one in his house and I'm pretty sure it had a humidistat and a thermostat. Made sense to me then, still does now.

[chad austin]

The Tjerlinde product didn't seem to have anything like that. At least 25 years ago a friend put one in his house and I'm pretty sure it had a humidistat and a thermostat. Made sense to me then, still does now.

Tom I agree, I was looking for something regarding that too. After looking into that particular power roof vent, it says that it's the "ice buster" or something like that and is meant to keep the attic below 32 degrees in the winter to prevent ice dams and doesn't have the correct controls for summertime.

How many vents are currently on the home? What is the "attic" SF? Length X width. You may not have enough roof vents installed as of now. Take a look at: Roof vent calculator and click on static roof vents, on the right hand side then on the right side of the second screen you will see where it says "how many roofing vents?" pick your sq footage and it will tell you how many vents you need on your roof.

[SkunkedAgain]

There are 11 vents in the roof along with soffit vents all around the perimeter. After we bought the house, I went through the attic and pulled the blown-in insulation back from the edges. According to that HSOforum, my 1,350sf attic requires anywhere from 3-9 vents depending on size so I'm pretty good with 11. I guess that it seems odd to need 11 roof vent fans but I guess that's how it goes.

[Tom7227]

Chad,

I understand the idea that a fan may screw up the natural flow of the air but if you are pulling enough out to lower the overall temp in the attic what's wrong with it? For example, I have a continuous vent ridge and soffit openings. There is also a gable end vent but only one one end. Should I somehow block that gable end vent and achieve better airflow? If I were to put a fan on it would it pull air through the ridge vent closest to the fan? Again, if I am moving more cfm wouldn't I also be keeping the temp lower?

Would it make a difference in the winter? I may be way off on this but I think part of the reason for air exchange in the winter is to get rid of humidity as well as keeping the temp down to prevent ice dams.

Just wondering.

Tom

[chad austin]

There are 11 vents in the roof along with soffit vents all around the perimeter. After we bought the house, I went through the attic and pulled the blown-in insulation back from the edges. According to that HSOforum, my 1,350sf attic requires anywhere from 3-9 vents depending on size so I'm pretty good with 11. I guess that it seems odd to need 11 roof vent fans but I guess that's how it goes.

Just another thought; look in the attic, up at the vents and make sure you can actually see the the vent. I have seen many incorrect roofing installations where the roofer forgot/didn't cut out the felt where the vent should be installed. You should be able to see 11 square holes in the sheathing and the "inside" of the vents.

Another thing that I want to be VERY CLEAR on is the possibility of creating negative pressure in your home if powered roof vents are used. Trying to exchange too much attic air can pull excessive make-up air from the interior of you home, from appliances that require it thus creating a back-draft in your flue pipe, pulling deadly gasses into the living space of your home. Not trying to scare anybody here but it is a real problem.

[chad austin]

Chad,

I understand the idea that a fan may screw up the natural flow of the air but if you are pulling enough out to lower the overall temp in the attic what's wrong with it? For example, I have a continuous vent ridge and soffit openings. There is also a gable end vent but only one one end. Should I somehow block that gable end vent and achieve better airflow? If I were to put a fan on it would it pull air through the ridge vent closest to the fan? Again, if I am moving more cfm wouldn't I also be keeping the temp lower?

Would it make a difference in the winter? I may be way off on this but I think part of the reason for air exchange in the winter is to get rid of humidity as well as keeping the temp down to prevent ice dams.

Just wondering.

Tom

Tom,

Being that air will move with the path of least resistance, the top 1/3 of your roof may exchange 10:1 to the bottom 2/3 of the roof. Soffit and ridge venting is designed to work as a static system. I would block the gable vent and let the soffit and ridge vents do their job. If you are having issues with ice damming in the winter then I would have a insulation company come out and check out your particular situation and have them also check to make sure that the attic is sealed from the house.

[K_Josh87]

I will second this, I have ran into these issues before... not so much ice damming, but I have seen where frost will form due to incorrect air flow... the gable vent and ridge vent only vent the top 3rd or so... i have seen this more than once be the actual issue... The continuous eve vent along with a continuous ridge vent, theoretically creates a perfect, continuous flow of air, from the eve to the peak, along the whole roof.... when this system is in correctly, and working properly, I have been in attics where there is a VERY noticeable proper flow of air... its actually kind of neat to be in an attic that the ventilation is working correctly...