Combining an Attic Vent Fan with a Roof Ridge Vent
Our contractor installed a ridge vent on our roof. We were still getting significant heat build up in the attic, so he then installed a solar roof fan that moves 500 CFM (cubic feet per minute). I noticed you said that these two systems should not be combined. Should we remove the solar vent fan? -Ron
Attics are vented using the natural circulation that occurs when hot air rises. Vents in the soffit beneath the eaves at the bottom of the attic draw in cool outside air while gable or ridge vents at the peak of the attic allow heated air to exit. In hot climates, a power vent fan is often mounted behind a gable vent or cut into the roof near the peak to assist this process by forcibly expelling additional hot air from the attic.
Combining an attic power vent fan with a ridge vent is usually not recommended because:
- It could reverse the natural flow of hot air out the ridge vent.
- If air is drawn in through the ridge vent while it’s raining, it might pull rainwater in with it, which could lead to leaking or mold in the attic.
While a power vent fan combined with a ridge vent can work against the natural flow of air through the attic, it will still exhaust more hot air than not having a fan at all, it’s just not the most efficient way to go about it.
Since your solar vent fan only moves 500 CFM (a third to half that of a typical hardwired attic vent fan), it probably won’t move enough air to reverse the action of the ridge vent. Also, since the fan is powered by the sun, it should turn off when the sky is overcast during a storm, which will keep it from drawing rain into the attic.
So, while it’s may not the most efficient way to cool an attic, in your case I would continue using the solar vent fan. You might want to check the attic occasionally when it’s raining to see if there is any water coming in the ridge vent.