Is a whole house fan compatible with a ridge vent?

Whole house fans are compatible with ridge vents as long as there is 1 square foot of ventilation for every 500 CFM capacity of the fan. For example, if you have a whole house fan with a rating of 4000 CFM the ridge ventilation should be more than (4000/500) = 8 sq.ft. If you have ridge ventilation for your attic I am pretty sure it has more area for attic vents than this.

Ridge ventilation needed (sq.ft) = CFM of whole house fan/500

How did I reach this ridge vent area calculation?

According to Energy.gov, the attic ventilation needed for a whole house fan is 1 sq.ft per 750 CFM capacity of the fan. So for a fan of 4000 CFM the attic should have a vented area 5.34 sq.ft (4000/750). But in the case of ridge vents, the available ventilation is limited since they come with screens. Therefore we need to add 50% more area for the ridge vents to match the ventilation requirements of whole house fans.

That means; Ridge ventilation needed = (CFM of whole house fan/750)x1.5

Since 1.5/750 is 500 the above equaltion becomes;

Ridge ventilation needed = CFM of whole house fan/500

Here is a table listing the size of the whole house fan, the area it can cool, and the ridge ventilation needed;

Whole house fan sizeArea of houseRidge ventilation needed
2500 CFM1000 Sq.ft5 sq.ft
4000 CFM1500 sq.ft8 sq.ft
5500 CFM2000 sq.ft11 sq.ft
7000 CFM2500 sq.ft14 sq.ft
9000 CFM3000 sq.ft18 sq.ft

Below is a graph showing the ridge ventilation needed based on the CFM of the whole house fan. As you can see it is a linear graph.

chart showing ridge ventilation for whole house fans

You can check my article whole house fan sizing guide to check what CFM your whole house fan needs to be.

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