O’Hagin Vent Calculator

Quick Vent Calculation Guide for O’Hagin’s Standard, WeatherMaster™, and Fire & Ice® Attic Vents

There are two important pieces of information required in order to calculate the adequate number of vents required for your project:

Determine the total square footage of the attic floor space to be ventilated.
You must know which code compliance method is required in the project area. Most local building codes require compliance with either the 1/150 method or the 1/300 method exception (refer to local code). These methods dictate that one (1) square foot of ventilation is provided for every 150 or 300 square feet of attic floor space. Compliance with attic ventilation code requirements should always be verified at the local governing level before performing the following calculations.

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Step 1: DETERMINE SQUARE FEET OF CODE-REQUIRED VENTILATION

Square Feet:

÷ Compliance Method

Calculate

=

Total Square Feet of Code Required Ventilation

Step 2: CONVERT SQUARE FEET OF CODE-REQUIRED VENTILATION TO SQUARE INCHES

x 144 = Total Square inches of Code-Required Ventilation

Step 3: DETERMINE THE ADEQUATE NUMBER OF O’HAGIN VENTS REQUIRED

Total O’Hagin Vents Required for sq. inches:

O’Hagin Tapered Low-Profile
72.0 sq. in NFVA

Vents High:
Vents Low:

O’Hagin High-Profile Model S
97.5 sq. in NFVA

Vents High:
Vents Low:

O’Hagin Low/Medium Profile Model M
86.25 sq. in NFVA

Vents High:
Vents Low:

O’Hagin Low-Profile Model Flat
98.75 sq. in NFVA

Vents High:
Vents Low:

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MANUFACTURER’S RECOMMENDATIONS
The patented O’Hagin Balanced Ventilation System utilizes O’Hagin vents placed strategically within the field of roofing material both high (near the ridge for exhaust) and low (near the eave for intake). This strategic high and low placement of O’Hagin vents allows the balanced system to fully optimize both wind and thermal effects to provide superior passive ventilation throughout the attic. Additionally, placement of O’Hagin vents both high and low should provide an equal, balanced rate of ventilation performance in each area. The calculations above do not include any potential Net Free Ventilation Area (NFVA) values provided by alternative ventilation methods that may be present in any specific structural design.

Code Required Attic Ventilation Calculations

÷ = x 144 = Total Square inches of Code-Required Ventilation

6 inch Extended Flange

6″ Extended Flange 72.00 sq. in NFVA

4″ Standard Flange 72.00 sq. in NFVA

Tapered, Low-Profile Vents For: Slate, Shake and Shingle Roofs

Exhaust/High Vents: Intake/Low Vents: Total Square Inches Provided:

Profile Specific Attic Vents For: Clay and Concrete Tile Roofs

Low-ProfileFlat	High-Profile‘S’	Medium-Profile‘M’

98.75 sq. in NFVA	97.50 sq. in NFVA	86.25 sq. in NFVA	86.25 sq. in NFVA

Exhaust/High Vents: Intake/Low Vents: Total Square Inches Provided:	Exhaust/High Vents: Intake/Low Vents: Total Square Inches Provided:	Exhaust/High Vents: Intake/Low Vents: Total Square Inches Provided:	Exhaust/High Vents: Intake/Low Vents: Total Square Inches Provided:

MANUFACTURER’S RECOMMENDATIONS

The patented O’Hagin Balanced Ventilation System utilizes O’Hagin vents placed strategically with in the field of roofing material both high (near the ridge for exhaust) and low (near the eave for in take).This strategic high and low placement of O’Hagin vents allows the balanced system to fully optimize both wind and thermal effects to provide superior passive ventilation throughout the attic. Additionally, placement of O’Hagin vents both high and low should provide an equal, balanced rate of ventilation performance in each area. The calculations above do not include any potential Net Free Ventilation Area (NFVA) values provided by alternative ventilation methods that may be present in any specific structural design.

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