Introduction
ASHRAE Standard 170, Ventilation of Health Care Facilities, is the foundational ventilation standard for healthcare facility design in the United States. Updated periodically, it establishes minimum ventilation requirements for spaces within hospitals, outpatient facilities, nursing facilities, and other healthcare environments.
For MEP engineers, understanding and correctly applying ASHRAE 170 is critical — not only for code compliance, but for patient safety, infection control, and energy performance.
Key Requirements
Air Change Rates
ASHRAE 170 specifies minimum total air changes per hour (ACH) and minimum outdoor air changes per hour for each space type. Some of the most commonly referenced requirements include:
| Space Type | Total ACH | Outdoor ACH | Pressure Relationship |
|---|---|---|---|
| Operating Room | 20 | 4 | Positive |
| Patient Room | 6 | 2 | Negative (Airborne Infection Isolation) or Neutral |
| Emergency Department Waiting | 12 | 2 | Negative |
| Pharmacy (USP 797) | 30+ | N/A | Positive (ISO 7 or better) |
| Laboratory (General) | 6 | 2 | Negative |
Pressure Relationships
Maintaining correct pressure relationships between spaces is essential for infection control. ASHRAE 170 defines whether each space should be positive, negative, or neutral relative to adjacent areas:
- Positive pressure rooms (e.g., operating rooms, protective environment rooms) prevent contaminated air from entering the space.
- Negative pressure rooms (e.g., airborne infection isolation rooms, soiled utility) prevent potentially infectious air from escaping.
- Neutral spaces have no specific pressure requirement relative to adjacent areas.
Temperature and Humidity
The standard also specifies design temperature and humidity ranges for healthcare spaces. Operating rooms, for example, typically require temperatures between 68°F and 75°F with relative humidity between 20% and 60%.
Design Considerations for Engineers
Energy Impact
Meeting ASHRAE 170 requirements often results in significantly higher energy consumption compared to commercial buildings. Engineers should consider:
- Energy recovery — Enthalpy wheels or plate heat exchangers on exhaust air can recover 50–70% of the energy that would otherwise be lost.
- Demand-controlled ventilation — Where permitted by the standard, reducing ventilation rates during unoccupied periods can yield substantial savings.
- Variable air volume (VAV) systems — Using VAV with appropriate minimums allows the system to respond to actual loads rather than running at maximum capacity continuously.
Coordination with Other Standards
ASHRAE 170 does not exist in isolation. Engineers must coordinate with:
- NFPA 99 — Health Care Facilities Code, which governs medical gas systems, electrical systems, and other life safety requirements.
- FGI Guidelines — The Facility Guidelines Institute publishes design guidelines that many states adopt as code, often referencing ASHRAE 170 for ventilation.
- USP 797/800 — For pharmacy spaces, United States Pharmacopeia chapters 797 and 800 impose additional ventilation and containment requirements beyond ASHRAE 170.
Common Design Pitfalls
Based on our experience across 50+ healthcare projects, the most common ASHRAE 170 compliance issues include:
- Incorrect pressure relationships — Particularly at transitions between clean and soiled spaces, or between isolation rooms and corridors.
- Insufficient outdoor air — Confusing total ACH with outdoor ACH requirements, leading to under-ventilated spaces.
- Missing redundancy — Critical spaces like operating rooms and isolation rooms require redundant systems to maintain ventilation during equipment failures.
- Inadequate commissioning — Pressure relationships and air change rates must be verified through functional performance testing, not just design calculations.
Evolve's Approach
At Evolve Consulting Engineers, we apply ASHRAE 170 requirements from the earliest stages of design. Our approach includes:
- Early coordination with architects and infection control teams to establish space pressurization maps before schematic design.
- Computational analysis of air change effectiveness to optimize diffuser placement and minimize short-circuiting.
- Energy modeling that accounts for healthcare-specific ventilation loads, allowing us to identify energy recovery opportunities early.
- Commissioning support through construction to verify that as-built systems meet the design intent.
Conclusion
ASHRAE 170 compliance is non-negotiable in healthcare facility design. However, meeting the standard's requirements while optimizing energy performance and constructability requires deep expertise and careful coordination across disciplines.
If you're planning a healthcare project and want to ensure your ventilation systems meet current standards while minimizing lifecycle costs, contact our team to discuss your project requirements.
This article is provided for informational purposes and reflects Evolve Consulting Engineers' interpretation of ASHRAE Standard 170. Always consult the current edition of the standard and applicable local codes for your specific project.