Crawl Space Ventilation Fans

How to Choose a Crawl Space Ventilation Fan

A crawl space ventilation fan mounts over an existing foundation vent and exhausts damp air from under the house, while replacement air comes in through the other vents. It suits vented crawl spaces where the outdoor air is drier than the air underneath. A sealed, encapsulated crawl space is usually dried with a dehumidifier instead.

Sizing by Airflow

Match fan CFM to the size of the crawl space. The VentirPro 260 is sized for 2,400ft³ to 3,600ft³, the 540 for 3,600ft³ to 5,600ft³ and the 720 for 5,600ft³ to 7,400ft³. The VentirMax 300, 570 and 780 cover up to 550ft², 950ft² and 1,300ft². Large or divided crawl spaces can take more than one fan on separate vents.

Controls

• Humidistat knob. Set a humidity level between 10 and 80 percent and the fan runs only while the crawl space is above it. VentirPro fans and VentirMax S models use this control.
• Programmable controller. VentirMax SD models and the dual fan VentirPro-S2 add humidity and temperature triggers, timed run cycles and five airflow levels.
• Freeze protection. A thermostat stops VentirPro and VentirMax fans in freezing weather, below 35 to 37 degrees Fahrenheit outdoors.

Housing

Aluminum-zinc housings cost less. Stainless steel housings, on the VentirPro S models and every VentirMax, stand up better to constant damp. Every model here has an insect screen behind the fan.

For sealed crawl spaces see crawl space dehumidifiers, or browse all dehumidifiers.

Frequently Asked Questions

Does a crawl space ventilation fan replace a dehumidifier?

Not in every case. A vent fan exchanges crawl space air with outdoor air, so it helps most when the outdoor air is drier. In humid climates or sealed crawl spaces, a crawl space dehumidifier controls moisture more reliably.

Where should a crawl space vent fan be installed?

Mount the fan over an existing foundation vent with its metal plate and four screws, trimming the plate to fit if needed. Replacement air then comes in through the other vents, so keep them open and clear.

Will the fan run in freezing weather?

VentirPro and VentirMax knob models have a thermostat that stops the fan below 35 to 37 degrees Fahrenheit outdoors and restarts it near 50 degrees. VentirMax SD models shut down below 37 degrees.

What is the difference between VentirMax S and SD models?

S models use a humidistat knob set between 10 and 80 percent relative humidity. SD models add a digital controller with humidity and temperature triggers, a timed cycle, five airflow levels and memory after a power cut.