Testing the effectiveness of a powered attic fan versus ridge vent and soffit ventilation.

Myth - A power roof ventilator will pull air from your roof ridge vent and short circuit the air flow from the lower eave soffit vents.

Fact - A powered roof fan will cool your hot attic space faster and more efficiently than ridge vent and soffit vents alone without compromising the venting system.

The video below demonstrates the fact. Please pardon the shakiness and lack of professionalism in the video. It was Hot, cramped, dusty and noisy.

The video was shot inside a smaller attic that is connected to a larger attic. This is inside a large home with a hip roof shingled with slate roofing material. There are large rectangular vents located along the soffit around the perimeter of the roof eaves. The roof peak has ridge vent installed along the entire length of the ridge.

The test was performed on a hot day, the outdoor temperature was about 80 degrees fahrenheit. The attic temperature was 92 degrees at the floor and 109 degrees at the peak.

At the start of the video we are looking from the smaller attic space towards the larger attic space. A smoke bomb has just been set off in the larger attic space and the smoke is starting to be seen flowing from the large attic to the small attic. The power vent is already running behind the camera in the hip end of the small roof.

As we progress we pan around the attic looking for signs of air being sucked in from other sources other than the attic spaces. Particularly the ridge/peak of the attic with the ridge vent. Extra time is spent looking between the rafters at the peak to see if the cobwebs are moving, which would indicate air being sucked in from outside at the ridge vent.

As seen there is no indication of air coming from the ridge vent which means there is no "short circuit " or disruption of airflow.

What is seen is the smoke, particularly visible against the beam of the flashlight,  from the far attic moving into and through the small attic and being exhausted through the powered attic fan.

Attic Ventilation Video

Conclusion : A powered roof attic fan will help to exhaust hot air from your attic, providing the attic has adequate soffit vent intake, with or without ridge vents.

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