O'Hagin's Quick Vent Calculation Guide
For Standard, WeatherMasterTM, and Fire & Ice® Attic Vents

An easy guide to determine the number of O’Hagin attic vents required for your project!

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

  1. First, determine the total square footage of the attic floor space to be ventilated.
  2. Secondly, 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.
THE REST IS AS EASY AS 1, 2, 3!
STEP 1 - DETERMINE SQUARE FEET OF CODE-REQUIRED VENTILATION
÷ Compliance Method: =
Enter Total Square Feet of
Attic Space to be Ventilated
  Select Required
Method
    Total Square Feet of Code-
Required Ventilation
STEP 2 - CONVERT SQUARE FEET OF CODE-REQUIRED VENTILATION TO SQUARE INCHES
x 144 =
Total Square Feet of Code-
Required Ventilation
    Total Square Inches of
Code-Required Ventilation
STEP 3 - DETERMINE THE ADEQUATE NUMBER OF O’HAGIN VENTS REQUIRED
÷ Net Free Ventilation Area
Value for O’Hagin Vents
= TOTAL VENTS REQUIRED
Total Square Inches of
Code-Required Ventilation
  Shown Below   Totals Shown Below for Each O’Hagin Vent Style (rounded to next even number where necessary for balanced ventilation system**)
- Vents High
- Vents Low

Tapered Low-Profile
72.0 sq. in NFVA
- Vents High
- Vents Low

High-Profile Model S
97.5 sq. in NFVA
- Vents High
- Vents Low

Low/Medium Profile Mode M
86.25 sq. in NFVA
- Vents High
- Vents Low

Low-Profile Model Flat
98.75 sq. in NFVA

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.