Compute air changes per hour from CFM and room volume, check NIH Guide compliance, assess heat load balance, and evaluate pressurization for vivarium rooms.
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Load example vivarium air change calculator data to see the full workflow
| Supply ACH | 0 |
| Exhaust ACH | 0 |
| NIH Status | ACH of 0.0 is below NIH Guide minimum of 10. Increase supply airflow. |
| Heat Removal Capacity | 0 BTU/hr |
| Heat Balance | Heat load (800 BTU/hr) exceeds removal capacity (0 BTU/hr). Room may overheat. |
When to use
Do not use for
The effective ACH is limited by the lesser of supply and exhaust. A room with 600 CFM supply but only 400 CFM exhaust has an effective ACH based on 400 CFM — the rest pressurizes the room.
IVC (individually ventilated cage) racks have their own blowers and may not depend on room ACH for cage-level ventilation — but room ACH still matters for heat removal and the workspace air.
Don't forget to account for people in heat load. During cage change, 2–3 technicians add 800–1,200 BTU/hr of sensible heat.
Measuring CFM at the diffuser is not the same as room supply. Duct leakage can reduce delivered CFM by 10–20%.
ACH is computed as (CFM 60) / room_volume_ft³ for both supply and exhaust. The effective ACH is the minimum of the two. Heat removal capacity uses the sensible heat equation: Q = CFM 1.08 ΔT (BTU/hr). Heat load sums cage and occupant contributions. NIH compliance thresholds: <10 ACH = below minimum, 10–15 = compliant, >20 = excessive.
Last validated 2026-04-08. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience Vivarium Air Change Rate Calculator (v1.15.0). ConductScience. https://conductscience.com/tools/vivarium-air-change-calculator
National Research Council. Guide for the Care and Use of Laboratory Animals. 8th ed. Washington, DC: The National Academies Press; 2011.
ASHRAE. HVAC Applications Handbook, Chapter 16: Laboratories. Atlanta, GA: ASHRAE; 2019.
The NIH Guide for the Care and Use of Laboratory Animals (8th edition) establishes environmental standards for animal housing. Section on Macroenvironment specifies:
The 10–15 ACH range balances three competing needs: 1. Gas dilution: Ammonia from urine must stay below 25 ppm (OSHA PEL) 2. Heat removal: A room of 200+ mouse cages generates significant sensible heat 3. Energy cost: Each CFM of conditioned air costs $2–4/year in energy
Modern facilities increasingly use demand-controlled ventilation (DCV) that modulates airflow based on real-time ammonia or CO₂ sensors, allowing ACH to drop to 5–8 during unoccupied periods while ramping up during cage changes. AAALAC accepts DCV systems that maintain adequate air quality as documented by environmental monitoring.
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