HVAC / MEPHVACConstruction Calculator
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ACH Calculator — Air Changes Per Hour

ACH measures how many times room air is replaced per hour. Critical for ventilation design, IAQ, and HVAC sizing. ACH = (CFM × 60) ÷ room volume.

Concept Fundamentals
4–6
Bedroom ACH
6–8
Bathroom ACH
7–8
Kitchen ACH
6–15
Lab ACH
Calculate ACHEnter room dimensions and CFM to verify ventilation

Why This Construction Metric Matters

Why: Insufficient ACH causes stale air, CO2 buildup, and pathogen spread.

How: ACH = (CFM × 60) ÷ room volume. CFM required = (volume × desired ACH) ÷ 60.

  • ●ACH = (CFM × 60) ÷ volume
  • ●Bedroom 4–6; bathroom 6–8; kitchen 7–8
  • ●15+ CFM per person (ASHRAE)
Sources:ASHRAE 62.1EPA IAQ

📋 Quick Examples — Click to Load

ft
ft
ft
Cubic feet per minute

Planning estimates only. Verify with a licensed engineer or contractor before construction.

📐 Construction Industry Facts

🌬️

ACH = (CFM × 60) ÷ room volume

— Ventilation

📐

CFM required = (volume × desired ACH) ÷ 60

— ASHRAE

👥

15+ CFM per person for occupied spaces

— ASHRAE

ACH (Air Changes Per Hour) measures how many times room air is replaced per hour. Critical for ventilation design, IAQ, and HVAC sizing. ACH = (CFM × 60) ÷ room volume. ASHRAE and CDC provide room-type recommendations. Bedrooms need 4–6 ACH; bathrooms 6–8; kitchens 7–8; labs 6–15.

60
Minutes per hour (CFM→ACH)
15
Min CFM/person (ASHRAE)
4–6
Typical bedroom ACH
6–15
Lab/hospital ACH

Sources: ASHRAE 62.1, EPA IAQ, CDC Ventilation Guidelines.

Key Takeaways

  • • ACH = (CFM × 60) / Room Volume (cu ft)
  • • CFM Required = (Room Volume × Desired ACH) / 60
  • • ASHRAE recommends 15+ CFM per person for occupied spaces
  • • Room types: Bedroom 4–6 | Bathroom 6–8 | Kitchen 7–8 | Lab 6–15

Did You Know?

🌬️ ACH measures how many times room air is replaced per hour; higher ACH = fresher air.
🏥 Hospital isolation rooms require 6–12 ACH; operating rooms may need 15–20 ACH.
💻 Server rooms need 10–20 ACH to remove heat from equipment.
🚿 Bathrooms need 6–8 ACH to control moisture and prevent mold.
📐 60 in the formula converts CFM (per minute) to per-hour rate.
⚡ Higher ACH increases energy use; balance ventilation with efficiency.

How Does ACH Work?

ACH from CFM

ACH = (CFM × 60) / Volume

CFM from ACH

CFM = (Volume × ACH) / 60

Activity Multiplier

Heavy activity (gym, kitchen) needs 1.5–2× base ACH.

Expert Tips

Measure interior dimensions; exclude furniture volume.
Heavy activity needs 1.5–2× base ACH.
ASHRAE: 15+ CFM/person for acceptable IAQ.
Bathroom/kitchen exhaust counts toward ACH.

ACH by Room Type

Room TypeMinMaxAvg
🛏️ Bedroom465
🚿 Bathroom687
🍳 Kitchen787.5
💼 Office465
📦 Warehouse6108
🔬 Laboratory61510

Frequently Asked Questions

What is a good ACH for a bedroom?

4–6 ACH for residential bedrooms. Higher if allergies or asthma. ASHRAE recommends minimum ventilation rates by occupancy.

How does CFM relate to ACH?

ACH = (CFM × 60) / Room Volume. CFM is airflow rate; 60 converts to per-hour. Example: 100 CFM in 960 cu ft room = 6.25 ACH.

What ACH for COVID/sick room?

CDC recommends 6+ ACH for isolation; consider HEPA filtration. Healthcare settings may require 6–12 ACH for infection control.

Why does activity level matter?

More activity = more CO2, odors, heat. Multiply recommended ACH by 1.2–2.5. Heavy exercise needs 2× base ACH.

Can ACH be too high?

Yes. Excessive ACH wastes energy and can cause drafts. Match to room use. Balance ventilation with efficiency.

How to measure existing CFM?

Use anemometer at supply/return grilles or consult HVAC professional. Balometer or flow hood for accurate readings.

Key Statistics

60
Minutes per hour
15
Min CFM/person
4
Typical bedroom ACH
6–15
Lab/hospital ACH

Official Data Sources

ASHRAE 62.1 ↗
Ventilation standards
EPA IAQ ↗
Indoor air quality
CDC Ventilation ↗
Healthcare ventilation
ENERGY STAR ↗
Efficiency guidelines

⚠️ Disclaimer: ACH values are estimates. For HVAC design, infection control, or code compliance, consult ASHRAE standards and a licensed HVAC professional.

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