CFM Calculator

Step 1: Calculate Room Volume

Start with your room's cubic footage:

• Room Volume = Length x Width x Height (in feet)
• Example: 12' x 10' x 8' = 960 cubic feet

Step 2: Determine Air Changes Per Hour (ACH)

Different rooms require different air exchange rates:

• Bedrooms: 0.5 ACH (quiet, minimal ventilation)
• Living rooms: 1.0 ACH (moderate activity)
• Bathrooms: 8 ACH (moisture removal)
• Kitchens: 15 ACH (odor and smoke removal)
• Garages: 6 ACH (fume removal)

Step 3: Calculate CFM

Use this formula:

• CFM = (Room Volume x ACH) / 60 minutes
• Example: (960 cubic feet x 8 ACH) / 60 = 128 CFM
• Add 15 CFM per occupant for fresh air

Step 4: Select Equipment

Choose fans and ducts based on CFM requirements:

• Round up to the next standard fan size (50, 80, 110 CFM, etc.)
• Duct size: larger ducts = less noise and energy use
• Consider static pressure for duct runs over 25 feet

Bathroom Exhaust Fans

Bathroom fans remove moisture and odors. Use these minimum requirements:

Kitchen Range Hoods

Kitchen exhaust requirements depend on cooking equipment and BTU output:

• Electric cooktop: 100 CFM minimum
• Gas cooktop: 100 CFM per 10,000 BTU
• Wall-mounted range hood: 100-400 CFM typical
• Island range hood: 150-600 CFM (higher due to cross-drafts)
• Professional cooking: 1 CFM per 100 BTU of burner output

Whole House Ventilation

Continuous ventilation for indoor air quality:

• Minimum: 15 CFM per occupant + 3 CFM per 100 sq ft
• Example: 4-person, 2000 sq ft home needs 120 CFM continuous
• Can be provided by ERV, HRV, or exhaust fans
• Balance intake and exhaust for proper operation

Duct Sizing Guidelines

Proper duct sizing reduces noise and energy consumption: