Vivarium HVAC and the NIH Guide
The NIH Guide for the Care and Use of Laboratory Animals (8th edition) establishes environmental standards for animal housing. Section on Macroenvironment specifies:
- Temperature: 68–79°F (20–26°C) for most rodents, with ±2°F stability
- Relative humidity: 30–70%
- Air changes: 10–15 ACH is the long-standing recommendation
- Ventilation strategy: 100% outside air is preferred; recirculation requires HEPA filtration
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.