HVAC CFM Calculator

CFM Calculator

Proper airflow is essential for HVAC efficiency and comfort. CFM (Cubic Feet per Minute) determines duct sizing, equipment selection, and overall system performance.

Understanding CFM

CFM measures the volume of air moved through your HVAC system:

• Definition: Cubic feet of air moved per minute
• Purpose: Ensures adequate cooling/heating delivery
• Too low: Poor comfort, hot/cold spots, longer run times
• Too high: Noise, drafts, wasted energy

CFM Requirements by Tonnage

Standard residential cooling requires 400 CFM per ton:

• 1 ton: 400 CFM
• 1.5 ton: 600 CFM
• 2 ton: 800 CFM
• 2.5 ton: 1,000 CFM
• 3 ton: 1,200 CFM
• 4 ton: 1,600 CFM
• 5 ton: 2,000 CFM

CFM by Room Type

For room-by-room distribution:

• Bedrooms: 1 CFM per sq ft
• Living rooms: 1-1.5 CFM per sq ft
• Kitchens: 1.5-2 CFM per sq ft
• Bathrooms: 1 CFM per sq ft (exhaust separate)

Factors Affecting CFM Needs

• Climate: Hot/humid areas may need more airflow
• Insulation: Well-insulated homes need less
• Ceiling height: Taller rooms need more CFM
• Windows: Rooms with large windows need more
• Occupancy: More people = more airflow needed

CFM and Air Changes

CFM relates to air changes per hour (ACH):

• Formula: ACH = (CFM × 60) ÷ Room volume
• Typical residential: 4-8 air changes per hour
• Example: 400 CFM in 1,000 cu ft room = 24 ACH