Worm Drive

Will installing a gable vent fan and gable vent have any negative affects in an attic that has soffit and ridge vents already installed? I remember reading that you should block off gable vents, if you're installing a ridge vent.

loneframer

The attic fan will pull air from the path of least resistance, starting with the ridge vent closest to the fan. Additionally, if the fan is not running, the ridge vent will draw air from the gable vent. However, I believe that as heat on the bottom of the sheathing naturally rises, it will still draw air from the soffit vents. A breaze will also cause areas of possitive pressure and negative pressure, causing air movement. How effectively the whole scenario will dissipate moisture is a mystery to me. I have soffit, ridge and a gable vent with a fan and haven't seen any ill effects to date.

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LNG24

I have yet to see an attice vent TOO MUCH heat from it.

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Larry Jensen, Broker/Owner
St. Lawrence Properties, LLC
LNG Contracting, LLC

genecarp

If you want the system to work efficiently, look at what the specs are on your fan(cfm). The spec will tell you how much intake surface area the fan needs to draw from. measure what you have , best estimate on ridge vent, and design accordingly.G

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delta l

My roof has full soffit vents front and back (66 linear feet); the attached garage also has front and back soffit vents. They are not blocked by inside insulation.

Booth roofs have ridge vents. Before my re-roofing, the ridge vent was metal with holes small enough to keep insects out. Afterwards, the vent was replaced with Cobra (tortuous path) vent.

I have never been able to demonstrate that air was pulled in at the soffits, nor discharged at the ridge, either before or after re-roofing.

My 2nd floor ceilings are R30, but it still gets hot upstairs, with insulation and vents. After the a/c shuts down for the day (due to cooling), the heat really builds up there.

What's a body to do?

Delta

rayh78

I no longer use them
About 10 years ago there was a long-term test by some university in Florida.
It had no effect on shingle life and actually increased the cooling cost of the houses in the test. Even in a well-built house it caused some of the cooling to be sucked up from the home into the attic. Around attic doors, light fixtures etc.
The overall conclusion has a powered attic fan did more harm than good

Worm Drive

Thanks for the replies. I'm hoping to make our upstairs more bearable on the 90+ deg. days.

LNG24

You are dealing with two DIFFERENT heat sources.

1) Radiant Heat: The attic is getting heat through the roof from the sun beating down on it. The ventilation helps prolong the life of the shingles, not cool the house down. There is supposed to be insulation between the attic and the living space so very little will be radiant

2) Heat Rise: Since heat rises, the heat from the main living area, radiant heat coming in from the windows, etc. is rising and getting trapped inside. This has nothing to do with nor will it be correct by the attic cooling.

You have two ways to resolve your issue.
1) Install AC up stairs and down stairs
2) Install a Whole House Vent Fan. This is a large fan that will evacuate all the air from your house. It pulls the air from outside in through an open window and exhausts it out the roof vents. The best version of the actually vents it directly outside and not just into the attic.

In the absence of installing either roof those, you can just practice proper air control. Keep windows open on the shady side of the house or at night. Close them up during the heat of the day to keep the hot air out of the house. Open Windows at the very bottom of the house and at the very top. Since heat rises, you will create a natural flow if it is cool enough outside.

Ceiling fans help too.


Good Luck

__________________
Larry Jensen, Broker/Owner
St. Lawrence Properties, LLC
LNG Contracting, LLC