How To Calculate How Many Roof Vents You Need
Balance is the key to having an efficient attic ventilation system. Calculating the correct number of exhaust and intake vents is simple and will ensure you have an effective, balanced system.
We must first calculate the net free area required. One square foot of ventilation is required for every 300 square feet of enclosed attic space, with half being exhaust and half being intake.
1. For a home with 3000 square feet of attic floor space you will need 10 square ft (3000/300=10) of attic ventilation.
2. Since you must have a balanced system, you divide by 2 (10/2=5) so that half of the ventilation is intake and half is exhaust.
3. Because vents are rated in square inches, you need to convert the square feet required to square inches (1sqft=144 sq inches).
4. In our example we need 5 sqft, thus 5×144=720 square inches of intake and exhaust. If we are using regular roof vents (50 sq inches each) and 10″ vented vinyl soffit (4.52 sq inches per foot) we would require 15 vents (720/50=14.4 – round up to 15) and at least 160 sqft (720/4.52=159.29) vented vinyl soffit to properly ventilate a 3000 sqft attic space.
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