--- title: How do you size foundation vents? description: Here is some information for sizing foundation vents. --- [Skip to content](https://help.gibraltarbuildingproducts.com/en/knowledge/how-do-you-size-non-powered-foundation-vents#main-content) English Show submenu for translations ![GBAD Full Color.png](https://blog.stealthbond.com/hubfs/GBAD%20Full%20Color.png) Open main navigation Close main navigation - English Show submenu for translations - Go to www.gibraltarbuildingproducts.com Go to www.gibraltarbuildingproducts.com Hello. How can we help you? - There are no suggestions because the search field is empty. 1. [Help Center](https://help.gibraltarbuildingproducts.com/en/knowledge?hsLang=en) 2. [Ventilation](https://help.gibraltarbuildingproducts.com/en/knowledge/ventilation?hsLang=en) 3. [Foundation Vents](https://help.gibraltarbuildingproducts.com/en/knowledge/ventilation?hsLang=en#foundation-vents) # How do you size foundation vents? ## Here is some information for sizing foundation vents. Whenever possible, vents should be placed on all sides of the foundation. This will create an intake/exhaust system that delivers a steady flow of air. One vent should be installed for each 8 to 10 feet of foundation wall. Most building codes require 1 square foot of open ventilation area for every 150 square feet of crawl space. For crawl spaces with polyethylene installed, on 80-90% of the floor, the ventilation requirement changes to 1 square foot of ventilation for every 500 square feet of crawl space with a minimum of 4 vents installed to provide cross ventilation. For crawl spaces with polyethylene, install at least one vent for every 500 square feet of crawl space. Avoid dead air spaces by placing vents within 3 feet of each corner. Dense shrubbery should be trimmed for the vents to be effective. Power Foundation Vents are designed for foundations that require a higher rate of airflow and for areas that are difficult to vent. Depending on the model they can move large amounts of air per hour. To determine the correct number of vents, use the following formula: 1) Multiply the square feet of the crawl space by the height in feet. This gives the number of cubic feet in the crawl space. 2) Multiply the cubic feet in the crawl space by the number of air changes per hour desired (4-6 is the recommendation). This gives the total number of cubic feet of air that has to be moved per hour to produce the desired number of air changes. 3) Divide this number by the published CFH (cubic feet per hour) specification by the vent manufacturer. That's the number of vents needed. 4) Install vents to provide air intake on one side of the foundation with the power vents on the other side to create a system of intake and exhaust.   - [Metal Roofing](https://help.gibraltarbuildingproducts.com/en/knowledge/metal-roofing?hsLang=en#main-content) - [Metal Roofing](https://help.gibraltarbuildingproducts.com/en/knowledge/metal-roofing?hsLang=en#metal-roofing) - [Oil Canning](https://help.gibraltarbuildingproducts.com/en/knowledge/metal-roofing?hsLang=en#oil-canning) - [SMRIB Profile](https://help.gibraltarbuildingproducts.com/en/knowledge/metal-roofing?hsLang=en#smrib-profile) - [5V Crimp Profile](https://help.gibraltarbuildingproducts.com/en/knowledge/metal-roofing?hsLang=en#5v-crimp-profile) - [Job Packs](https://help.gibraltarbuildingproducts.com/en/knowledge/metal-roofing?hsLang=en#job-packs) - [Roofing Accessories](https://help.gibraltarbuildingproducts.com/en/knowledge/metal-roofing?hsLang=en#roofing-accessories) - [Rainware & Gutter](https://help.gibraltarbuildingproducts.com/en/knowledge/rainware-gutter?hsLang=en#main-content) - 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