Attic Ventilation Calculator

Enter your attic dimensions and vent types to calculate the required net free area (NFA) for balanced intake and exhaust ventilation — with vent counts and cost estimates.

Attic Length (ft)

Attic Width (ft)

Ventilation Ratio (IRC)

Intake Vent Type

Exhaust Vent Type

Pricing (edit to match local rates)

Intake Vent ($/section)

Exhaust Vent ($/4-ft section)

Total NFA Required

1075 sq in

Attic: 1,120 sq ft | Ratio: 1/150

Intake Vents Needed

576 sq in NFA provided

Exhaust Vents Needed

576 sq in NFA provided

Total Vent Cost

$280.00

Intake $120.00 + Exhaust $160.00

Purchase Option	Quantity	Est. Cost
Intake: Continuous Soffit	8 8-ft sections	$120.00
Exhaust: Ridge Vent	8 4-ft sections	$160.00

Balanced ventilation: 50/50 intake-to-exhaust splitThe IRC requires a balanced system with roughly equal intake and exhaust NFA. Slightly more intake than exhaust is ideal — this creates positive pressure in the attic, which prevents moisture-laden air from being pulled through gaps in the ceiling. Use the 1/300 ratio if you have a vapor barrier and balanced intake/exhaust; otherwise, use the more conservative 1/150 ratio.

This is a ventilation estimate based on IRC 1/150 and 1/300 rules. NFA ratings vary by manufacturer — always verify the NFA rating printed on the vent you purchase. Local codes may have additional requirements.