Crawl Space Fans

CFM (Cubic Feet per Minute) determines air movement volume. Calculate based on crawl space size and desired air change frequency.

Quick Calculation:

1. Calculate volume: Length × Width × Height (in feet) = Cubic Feet
2. Choose target air change interval (2-5 minutes)
3. Divide: Cubic Feet ÷ Minutes = Required CFM

Examples:

• 1,000 cu ft crawl space: 500 CFM for 2-minute changes, 250 CFM for 4-minute changes
• 2,400 cu ft crawl space: 1,200 CFM for 2-minute changes, 600 CFM for 4-minute changes

Fan Capacity Guide:

• 460 CFM: Up to 1,800 cu ft (2-minute changes)
• 850 CFM: Up to 3,400 cu ft (2-minute changes)
• 1,115 CFM: Up to 4,500 cu ft (2-minute changes)

For spaces over 4,000 cu ft, consider multiple fans or professional consultation.

Choose based on your crawl space configuration and moisture strategy.

Exhaust Fans - Remove Air to Exterior:

• Use when: Outdoor air is drier than crawl space air
• Requires: Exit point (foundation vent) and adequate intake vents for replacement air
• Best for: Traditional vented crawl spaces in dry climates
• Types: Shutter fans (wall-mount), foundation vent fans, modular exhaust systems

Circulation Fans - Move Air Within Space:

• Use when: Dead zones exist with stagnant air, or supplementing a dehumidifier
• No exit point needed
• Best for: Distributing dehumidified air, targeting specific problem areas
• Types: Portable modular fans with flexible positioning

Warning: Exhaust fans can introduce MORE moisture in humid climates when outdoor air is more humid than crawl space air. Pair with humidistat controllers for smart operation.

Continuous operation is possible but not always beneficial—smart controls optimize performance.

Equipment for Continuous Use:

• Energy-efficient motors rated for continuous duty
• Our fans handle 24/7 operation without overheating
• Three-speed controls allow matching airflow to conditions

When Continuous Operation Works:

• Circulation fans distributing dehumidified air
• Very humid climates with persistent moisture problems
• Supplementing dehumidifier in large crawl spaces

Why Continuous Isn't Always Best:

• Exhaust fans introduce moisture when outdoor humidity is high
• Wastes energy during favorable outdoor conditions
• Can over-dry in winter, creating static issues

Better Approach - Humidistat Control:
Automatically operates fan only when outdoor air is drier than crawl space air. Conserves energy and prevents introducing humid air during unfavorable conditions.

Typical Operation: Intermittent cycles (15-30 minutes per hour) often more effective than continuous operation.

Fans and dehumidifiers serve different purposes—many spaces benefit from both.

Dehumidifiers: Extract water from air regardless of outdoor humidity. Essential for encapsulated crawl spaces. Work 24/7 to maintain target humidity.

Fans: Move air but don't remove moisture. Exhaust fans only work when outdoor air is drier.

When You Need Both:

Dehumidifier + Circulation Fan:

• Medium/large encapsulated spaces (800+ sq ft)
• Dehumidifier conditions air immediately around unit; circulation fan distributes throughout space
• Prevents humidity stratification and dead zones
• Improves dehumidifier efficiency

Fan Alone May Work:

• Traditional vented crawl space in consistently dry climate
• Outdoor air reliably drier than crawl space

Dehumidifier Alone Works:

• Small encapsulated space (under 800 sq ft) with good natural circulation
• No significant dead zones or obstructions

Best Approach: Dehumidifier for moisture removal + circulation fan for air distribution in larger spaces.