Attic fan with ridge venting

Local Inspection Issues Florida and SUNachi Inspectors
1

Hello all,

I haven’t had time to google this as I just finished the inspection. The house has
a gable roof with recently updated ridge and soffit ventilation. There is a rather large attic fan mounted 5 feet from the beginning of the ridge vent. The fan box (still in attic) states moves 1600 sqft of air.
Common sense says the fan is counter productive to the ridge venting. I know this is beyond the scope of an HI, but I want to absorb as much knowledge as possible.
So what do you guys/gals think?

2

You need to verify if the fan is on a thermostat or a simple switch within the home. If it’s oversized it will simply draw more air out.
1600 Sf of air per minute? What’s the entire volume of the attic? Will the size of the soffit vents allow for this type of draw or will you merely be drawing air from the ridge vent and perhaps out of the living space itself? A negative attic pressure could then draw cold air from within the conditioned space if it’s not properly balanced. Lots of variables.

3

Yes it has a thermostat set at 100deg.

The box stated 'moves up to 1600sqft (no time)

The house is 2900 sqft plus 650 garage.

I attached a spiderweb (all I had) to the ridge vent close to the fan and it appeared to be blowing down and toward the fan.

There are approx’ 10 recessed light cans located very close to the fan as well.

Thanks Mr. Elliot. All good points

4

"]http://www.buildingscience.com/documents/insights/bsi083-mea-culpa-roofs](http://www.buildingscience.com/documents/insights/bsi083-mea-culpa-roofs/URL)

5

http://www.baileyeng.com/wp-content/uploads/2014/08/THE-PASTON-EFFECT2.pdf

6

Thanks Fred,
I appreciate that info.
Helped a lot.