Which side of attic to install gable exhaust fan?

[jeromedawg]

Hi all

Was wondering which side of the attic to install a gable exhaust fan. It looks like the prevailing winds are from the west in my area (south orange county, ca) and our house is facing west (very slightly south westerly). So the ventilation in our attic seems pretty poor given the position. We have no soffit vents in the front and there are no roof or ridge vents (spanish clay tile roofing makes this difficult) so there is not much air that naturally gets pulled in from what I can tell.

I'd be inclined to have the fan installed on the north side. Our neighbor has one installed on the north side of their attic as well. Our attic is a bit odd as there are 3 sections of 'split' roofing. One gable vent is on the end where the shortest roof/attic height is, and another vent is right in the middle. The north side vent is highest up in the attic i think. Since heat rises, it seems placing it there would make the most sense (despite the south westerly orientation not being ideal and potentially counteracting an exhaust fan being positioned like that.).

Thoughts? I'll probably just buy the fan and have my HVAC contractor or electrician install. Going up on a ladder inside of our attic and trying to DIY electrical and mounting work just seems like an accident waiting to happen.

Any suggestions on fans? Quietcool? The attic is probably anywhere from 1300-1600sq ft.

[ChpBstrd]

My understanding is that you have three levels of gabled roof with the planes facing roughly east-west, and all your gable vents face north. Correct?

In that case I like your idea, but there may be better passive options to get airflow that don't burn electricity all the time. If you could install a few square feet of soffit vents, you might find that makes a huge difference in the way air flows into the attic and out of the existing vents. Right now, air is only exchanged when the attic gets so hot the air flows out of the higher vent and outside air is sucked into the lower one. All vents are facing the same direction as I understand, so wind can interfere, especially since wind speeds are generally higher at the higher elevations.

Take a look at your soffits. If they are just painted wooden boards, you can easily hack out 5-6 rectangular holes and tack on some inexpensive soffit vents like these:

https://www.lowes.com/pd/Master-Flow-Undereave-16-in-L-White-Aluminum-Soffit-Vent/999972080

If the soffits are solid siding, explore whether you could replace a few soffit pieces with perforated siding material and open up an air channel into the attic. If the home was originally built with siding, it will probably not be solid wood under the existing siding.  So this scenario is an especially easy fix. If the siding was added later, you might remove the solid soffit while being careful not to tear up the channel pieces, saw out the old underlying soffit boards to expose the attic, and then replace the soffit with perforated material. You might even find that siding was added and covered up the old vents!

I suggest focusing your vent additions on the upwind west side of the house, so the house itself scoops incoming air up into the soffit vents, the air blows through the attic, heats up, and exits through the existing north-facing gable vents. If it seems simpler and you have a west-facing porch, consider putting a several of these vents in the ceiling there. A porch will act as a natural air scoop too, although it won't distribute the airflow across the hot roof deck as well as soffit vents.

[snic]

Generally there isn't much point to adding electric attic ventilation. If there isn't adequate ventilation to begin with, all a big, powerful fan is going to do is draw conditioned air from the house into your attic. Do you really want to pay to air condition your attic?

As pointed out above, adding passive ventilation if it is insufficient is a far better option. It's also important to realize that attics are *supposed* to be hot. Ventilation is more to control humidity, although sufficient ventilation will also keep it a bit cooler. Your roof tiles are absorbing an enormous amount of heat in full sun, which is going to keep the attic underneath incredibly hot - and the fan you would need to keep the attic at the outside temperature would have to be very powerful and use a lot of electricity.

So, the best option, if you are worried about the hot attic making the floor below it too hot, is to seal all the penetrations between the attic and the living space, then add insulation to code or beyond. That can be done after adding adequate passive ventilation; just make sure that you install baffles so that soffit vents don't get covered with insulation.