Attic fan installation questions

Hi all,

I have read several posts (Chandler and Airman posted in them) debating attic fans versus turbines. I hate the idea of cutting holes in the roof which is why I am leaning away from turbines. Also, as my house has gable vents on both sides, I can move the air if I put a fan there. I'm ok with the cost of running the fans versus the savings I think I'll see from my AC running less. If the fan goes out, well, I'll fix it or else I'm back to where I started. I bet the $85 fan will pay for itself in two months in North Carolina.

Installation:
-I've read how people install them with rubber washers/bushings to cut vibration and I plan to do that.

-I also read people installing them onto plywood and about making sure that outside air can't enter from immediately outside the fan shroud and just get blown out immediately. SO - for those people that install these on plywood, are they suggesting to cover 100% of the existing gable vent with plywood and cut the hole where the fan will be mounted?

-Or, do people typically build a box, mount the fan on the box, and hang that in the center of the gable vent (and not worry that it doesn't cover the entire gable vent).

-If my existing gable vent has screen on it, should I remove it and then put screen on the attic side of the fan once I've installed it? I'm thinking about how the fan might clog up the existing gable vent screen if I put the attic fan over it.

Thanks,

Chris

 

Chris, I would use the gable vents with a fan, since that is what you have. Installing the mushrooms and cutting holes in an otherwise non leaking roof would not be beneficial. Yes, for a complete flow of hot air from the attic, building a box, or occluding any air from coming in the perimeter of the fan is the way to go. Some fans are mounted in a box that attaches to modified studwork over the gable area, and you seal it up. Toss up on the screen, but if you are mounting it permanently, I would remove the screen from the gable vent itself and install one on the fan inlet side so you can clean it.
Main thing is complete movement of old air, and no reintroduction of new air unless it is coming from another location such as the opposite gable or soffit vents.

 

Happy Wednesday I agree! I will add a soft and ridge vent would be best

 

I will also add that you need to seal the attic well also. Any air leakage will be multiplied when you create the negative airflow by installing the fan. Any holes in the ceiling will cause that air conditioning to be drawn into the attic!!

 

I was going to mention the ridge vent, but figured it may be counterproductive since he had gable vents and planned on a fan. Thinking was, it would restrict the flow of lower air in the attic and only pull in the air from the ridge. You know me, I am for passive energy, and a ridge vent would be best, but his cards are dealt with the gables unless he occludes them. Thoughts??

 

What is wrong with me. I agree gable would reduce any advantage that soft and ridge will provide. Air sealing is over rated homes need 60 to 90 cfm of fresh air for good IAQ

 

Thnaks, y'all! Last question: I'm adding the fan to a circuit that has (up until now) been dedicated to the outlet on the garage ceiling that supports the garage door opener. I was going to add the attic fan leg starting at that outlet box. This outlet is not a GFCI outlet. Do you think it's ok to leave as-is, or is it more than worth the $12 cost of the GFCI outlet to change it to GFCI?

Sincerely,

Chris

 

Good point badeyeben; another issue I have with the house (built 1977) is that the roof trusses shrink during the winter (when humidity drops) and pull the ceiling sheetrock away from the wall sheetrock at the corners. This winter was particularly bad for that and I had upwards of a 3/8" gap at some spots. During the summer, the trusses set back down and leave no gap. I could tell that it had been attempted to be sealed with caulk when it was last painted but that didn't work (nor would I have expected it to). This gapp occurs in the kitchen (at the end closest to the middle of the truss, where the bow would be most pronounced) and both bathroom showers.

Have you dealt with this before? Do you think i should wait for it to happen again, insert some shim material to fill the gap and then seal that with a rubberly caulk? I guess that would leave a slight but permanent bow in my ceiling/wall corners but I like that better than seeing the gap open up every winter.

 

Don't place the motor on a GFCI receptacle. It is basically inaccessible by personnel and may have nuisance trips due to the motor and the heat.

 

Hi all, I installed the fan in september 2011 and it hadn't come on yet. I went into the attic and used a hair dryer to heat up the thermostat and viola the fan came on. That's good. As I watched it work, though, it raised several questions:

1) Per the instructions, I installed the thermostate on the stud adjacent to the fan. Thus, my thermostat is hung on one of the studs to which the fan is mounted. This places the themorstat right next to the gable vent to the outside. The question: if the thermostat is so close to the outside, it seems like the areas of the attic farthest from the vent will have to get super hot in order to trigger the thermostat to hit 105 degrees. Have other people felt this way and moved the thermostat farther away from the gable vent? I realize the result will be that the fan will run more and perhaps run so long that it uses more electricity and gets more wear than is practical in the big-picture view of why people use these fans anyway. Thoughts?

2) There is a 1.75" gap (the thickness of a 2*4) between the 'front' edge of the fan housing and the gable vent. My gable vent is wooden and the slats are 45 degrees. Certainly there is some resistance when the fan tries to blow air through it: I expected this. However, there seems to be a significant amount of air 'spilling' through the 1.75" gap. Thus, it feels like instead of pushing air through the vent, a lot of it is just spreading out as it hits the vent and not really exiting the attic. Do people typically built boxes or cut out circle in some plywood to mount between the fan and the gable vent in order to eliminate such gaps?

3) This goes back to my decision between using a square vent whose flaps open by the force of the air when the fan comes on or leaving in place the existing gable vents. It seemed like a lot of unnecessary cutting to cut out a square in the middle of a gable vent just to install the vent that the fan manufacturers market to go with the fan.

4) I have a picture - if someone could briefly share how people share pics on this forum nowadays (photobucket used to be popular) then I'm happy to post them.

-Chris

 

Chris: http://www.doityourself.com/forum/el...your-post.html should help.
1) The thermostat is placed there so the air will ride over it. Once it cools down, it will signal for the fan to turn off.
2) Some people flash the edges of the fan so it is pulling 100% of the air through it. IMO, you are getting a pretty good flow even with the gap, but if you feel it is not, then, by all means, flash around it.
3) I would use a blank fan up to the original vent slats, mainly for aesthetics from the outside. The vent slats should have wire cloth over them to prevent infiltration of animals.
4) By all means, post pix!!