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Air Changes per Hour

Calculate room air changes per hour (ACH) from supply airflow and space volume.

Author

Dr. Lars Eriksson

HVAC editorial contributor

Swedish environmental economist from Stockholm School of Economics, advisor to the EU on carbon pricing policy

Reviewed by

Prof. Rajesh Sharma

HVAC content reviewer

Indian agricultural economist from IARI New Delhi, advising governments on food security under climate change

Last updatedFebruary 22, 2026

PublishedFebruary 22, 2026

On this page

  1. Reference values
  2. Calculator
  3. Reference table
  4. FAQs
  5. Methodology and review
  6. Related conversions

20×15×9 ft room at 100 CFM =

2.22 ACH

Representative value from the Air Changes per Hour reference table.

Reference Values

Browse 36 reference values with individual detail pages for quick lookup.

Browse all reference values

ACH Calculator

Calculate ACH from airflow or find required airflow from target ACH.

ACH Result

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Reference Table

Use this complete table for quick lookup and internal linking to specific value pages.

Air Changes per Hour Reference
ScenarioACHRoom Volume (ft³)
10×10×8 ft room at 100 CFM7.5 ACH800
10×10×8 ft room at 200 CFM15 ACH800
10×10×8 ft room at 300 CFM22.5 ACH800
10×10×8 ft room at 400 CFM30 ACH800
10×10×8 ft room at 600 CFM45 ACH800
10×10×8 ft room at 800 CFM60 ACH800
12×12×8 ft room at 100 CFM5.21 ACH1,152
12×12×8 ft room at 200 CFM10.42 ACH1,152
12×12×8 ft room at 300 CFM15.63 ACH1,152
12×12×8 ft room at 400 CFM20.83 ACH1,152
12×12×8 ft room at 600 CFM31.25 ACH1,152
12×12×8 ft room at 800 CFM41.67 ACH1,152
15×12×8 ft room at 100 CFM4.17 ACH1,440
15×12×8 ft room at 200 CFM8.33 ACH1,440
15×12×8 ft room at 300 CFM12.5 ACH1,440
15×12×8 ft room at 400 CFM16.67 ACH1,440
15×12×8 ft room at 600 CFM25 ACH1,440
15×12×8 ft room at 800 CFM33.33 ACH1,440
20×15×9 ft room at 100 CFM2.22 ACH2,700
20×15×9 ft room at 200 CFM4.44 ACH2,700
20×15×9 ft room at 300 CFM6.67 ACH2,700
20×15×9 ft room at 400 CFM8.89 ACH2,700
20×15×9 ft room at 600 CFM13.33 ACH2,700
20×15×9 ft room at 800 CFM17.78 ACH2,700
25×20×10 ft room at 100 CFM1.2 ACH5,000
25×20×10 ft room at 200 CFM2.4 ACH5,000
25×20×10 ft room at 300 CFM3.6 ACH5,000
25×20×10 ft room at 400 CFM4.8 ACH5,000
25×20×10 ft room at 600 CFM7.2 ACH5,000
25×20×10 ft room at 800 CFM9.6 ACH5,000
40×25×12 ft room at 100 CFM0.5 ACH12,000
40×25×12 ft room at 200 CFM1 ACH12,000
40×25×12 ft room at 300 CFM1.5 ACH12,000
40×25×12 ft room at 400 CFM2 ACH12,000
40×25×12 ft room at 600 CFM3 ACH12,000
40×25×12 ft room at 800 CFM4 ACH12,000

Frequently Asked Questions

Common questions about Air Changes per Hour, formulas, and typical use cases.

What is ACH in HVAC design?

ACH means air changes per hour and indicates how many times the room air volume is replaced each hour.

How is ACH calculated?

ACH = (CFM × 60) / room volume in cubic feet.

Can I calculate required CFM from target ACH?

Yes. Rearranging gives CFM = (ACH × room volume) / 60.

Is higher ACH always better?

Not always; target ACH depends on occupancy, use type, comfort, and energy goals.

Methodology and Review

This page combines a live calculator, precomputed reference values, and FAQ content from the same conversion definition to reduce mismatch between calculator output and lookup tables.

Editorial metadata (author, reviewer, and update date) is rendered on the page and in structured data. See our editorial policy, review process, and corrections policy.

For compliance-sensitive work, verify final values against project requirements, governing standards, and manufacturer documentation.