Attic temps

[George Hardy]

Hi everyone, stumbled across the forum as I was searching for common attic temperatures to justify my success or failure to get air moving in my attic. Experimented first in my detached garage by installing a gable fan in reverse so that it pushes air to the back of the garage attic . The mounting is one foot away from the intake vent; it is sucking air from the gable as well as two eve vents ( added more along the eve also). Distance to the exhaust vent is 31 feet. Replaced the exit vent with a home made one to increase air flow; gave me a nice outflow as attic temp is about 105 at 1:28 pm, ambient temp is 89 in Southern New Jersey. There is a small table fan near the exhaust to assist ( temporary) Not bad, even with the assist fan off there is a nice outflow.
House attic has a similar setup with temporary floor fan as a " pusher" ( again temporary ) but there is an air handler in the way decreasing the effectiveness of my setup. This attic has a ridge vent as well as eve vents in place. Got a real nice Wireless Thermometer from Walmart for 10 bucks so I don`t have to keep going into the attic for readings ( Acurite model 02044 W)
Current readings: ambient air outside 89
inside 74 with HVAC
attic 117
At this point, from reading other posts, I`m guessing my results are very good. Most likely will replace the house exit vent with a home made one to increase exit air flow. The plastic commercial one is just plain useless. Only working ok because the fan is 4 inches away from it. Your opinions are appreciated. thanks

[Brian Hannigan]

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[Jerry Peck]

Your description sounds like you are depressurizing the attic (blowing attic air out/sucking attic air out, either one one creates the same effect).

When you depressurize the attic, that air has to ... HAS TO ... come from someplace else, and it is likely that some, little or a lot, is coming from inside the house. :(

I.e., you are sucking your air conditioning into the attic, so, yes, the attic will be cooler :) ... but the air conditioner will have to work harder to cool the inside of the house :( because ... the air being sucked from the house into the attic has to ... again, has to ... come from someplace else, and that would be the outside air. :(

At least that is what I am getting from your descriptions.

[Egbert Jager]

Jerry has (as usual) some great points. Passive ventilation really should be enough to get the ventilation you need, but you have to consider where the air is entering as well as where it's exiting. Typically here in Calgary, there simply isn't enough of either and we enjoy temperatures from -30 to +30 (yes Celcius :rolleyes:) sometimes in the same week!

And when there 'appears' to be venting, turns out the vented soffit was installed over solid plywood, or there are no baffles and the insulation is pressed against the roof sheathing.

As for roof vents, the roofers sometimes cut a 4"x4" hole for the plastic 'turtle back' vent (that is listed as a vent of 50 sq inches net free area), or they calculate the vent as 1/2 sq foot and so don't install enough, or the vents end up getting buried under a foot of snow...

Good lucks with your venting improvements!

[John Kogel]

If you have ridge venting, you should cover the gable vents to prevent air from coming in there.

Make sure you have clear soffit vents between every rafter. If you had to add some to your garage, probably similar for the main house.

Depending on when the house was built, you can get a lot of leakage from below, especially at light fixtures and wall junctions.

A full length ridge vent with full length soffit vents gets air moving nicely, no fans needed as a rule.