[kmc]

Just installed an attic gable fan. I cut a hole in plywood, and mounted the fan on the board, and then bolted it all to the gable. The fan fits pretty tight against the plywood and there is little room for air to escape and recirculate. The fan is on a wall switch and set to 80 F. I leave it off while at work. I also have a wireless thermometer in the attic. The readings I get before using the fan so are from 100 F to 120 F so far (two days).

The issues I'm having is right when I fire it up, the temperature suddenly starts to rise and continues for a while. It will work eventually later in the evening when the outside temp starts to go down but not until then. It has been one hour now at 73 F outside temp since turning the fan on and the temp in the attic went from 104 F to 109 F.

Inlet:

Sofits: 7 on north wall and 1 on south wall. Each- 1" x 8" w/ screen

Gable vent: identical to the one the fan is attached to (~14.5 x 19" slotted) on opposite wall.

Outlet:

15", 1300 cfm gable fan in 15" diameter circular area.

Attic area:

~1,250 sqft

What is wrong here, and what would you do to fix it if this was your house? Thanks

 

[yuri]

Is your attic hatch sealed well? Heat rises and if you create a draft/negative pressure you may be sucking heat upwards from the house into the attic. Obviously it would have to be hot under the hatch and we don't know the house temp there.

 

[kmc]

Is your attic hatch sealed well? Heat rises and if you create a draft/negative pressure you may be sucking heat upwards from the house into the attic. Obviously it would have to be hot under the hatch and we don't know the house temp there.

House is about 73 F and the hatch is sealed o.k., not great, just o.k. I plan to overhaul the attic one day and replace the insulation and duct work. The original 1973 insulation is still there under a mickey mouse job of flopped home depot insulation sheets that the former owner did. It all needs to be removed and replaced along with some support boards and mastic, etc. I believe the inspector mentioned that the ridge vents may be covered over if that will make any difference here. I have not verified this yet.

 

[Hubcap626]

I don't know much about attic venting but make sure all you soffit vents are clear and nothing is blocking them. That is where you will be getting all your fresh air as hot air rises. So I would assume you don't have enough fresh air intake to cool down the space. You will only get the attic down so much as well, attics can get pretty hot, I would assume up to 130-140. So if it's 80 out and the space is 130, and your getting it down to 110 I would say that's pretty good. But don't quote me on that I don't know what kinds of temperature your looking for.

 

[yuri]

There is a tremendous heat gain/solar gain if you have dark shingles and depending on the time of day and exposure it will transfer thru them into the attic. You may be gaining heat faster than the fan can exhaust it and that may be normal. I face due West and from 3pm to 8 pm get a lot of that.

 

[kmc]

One thing I just noticed is that my gable vent is a little plugged up. If you zoom in you can see it. I think I will try to poke out the blocked holes in the screen and see if it helps. Also, does anybody know if I can just simply cut bigger sofit holes and install new vents? I have a new multi tool that would be perfect for that.

 

[Hubcap626]

One thing I just noticed is that my gable vent is a little plugged up. If you zoom in you can see it. I think I will try to poke out the blocked holes in the screen and see if it helps. Also, does anybody know if I can just simply cut bigger sofit holes and install new vents? I have a new multi tool that would be perfect for that.

You might want to check with a roofer about those Sofits. Thy does not look like much of an opening to me. How many of them do you have? Make sure no insulation is blocking them.

 

[clocert]

You need at least 10 of those holes at the other side of the attic.

 

[Gary in WA]

Your soffit vents are grossly undersized. 1"x8" with screen = maybe 5 sq.in.NFVA which should be 9 NFVA per lineal ft. With 1/2 at each side, together they meet the exhaust NFVA; http://www.airvent.com/homeowner/products/intakeSoffit-specs.shtml Total divide by 150... The gable fans will suck air from the living space or other gable end, or ridge vent, whichever is easier- before the soffits.

Gary

 

[beenthere]

Depending where you have your sensor located. It may not be sensing the true attic temp. And when you turn the fan on, it senses the true attic temp.
Relocate your sensor.

Better to leave the fan run anytime the thermostat calls for it, then to leave it off all day until you come home.