ANSI/ASHRAE/ASHE Standard 170, Ventilation of Health Care Facilities, is the code-referenced basis for how every occupied space in a hospital or outpatient facility is conditioned and ventilated. Its design-parameter table (Table 7-1 in recent editions; Table 7.1 in earlier ones) is the single most consulted artifact in healthcare HVAC design, defining the minimum performance every room must meet.
Standard 170 sets minimum ventilation and conditioning requirements; it is a floor, not a target. It is co-published with ASHE (the American Society for Health Care Engineering) and is adopted by reference inside the FGI Guidelines (both the Hospitals and Outpatient volumes), which is how it gains regulatory force. When a state's authority having jurisdiction (AHJ) adopts a given FGI edition, the matching Standard 170 edition becomes enforceable. CMS Conditions of Participation and The Joint Commission both look to FGI/Standard 170 as the recognized ventilation reference.
Standard 170 covers the requirements for new construction and major renovation. Existing systems are generally allowed to remain at the code in force when they were built, unless a renovation triggers compliance for the affected area.
The core of the standard is a single large table that lists every defined space type and, for each, the design parameters that govern it. Reading a row of the table tells the designer exactly what that room must achieve:
| Column | What it specifies |
|---|---|
| Pressure relationship | Positive (+), negative (−), or no requirement (NR) relative to adjacent spaces — see hvac pressure relationships |
| Minimum outdoor ach | Outdoor (fresh) air changes per hour the system must deliver |
| Minimum total ach | Total supply air changes per hour, including recirculated air |
| All air exhausted directly | Whether room air may be recirculated or must be exhausted to outdoors |
| Air recirculated by room units | Whether fan-coil / room-level recirculation is permitted |
| Design relative humidity (%) | Allowable RH range for the space |
| Design temperature | Allowable dry-bulb temperature range |
Filtration requirements are set separately by space category (see below), not by an individual table column in every edition. The table is grouped by functional area — surgery and critical care, inpatient nursing, radiology, nursing facilities, sterile processing, support, and so on.
The values below illustrate how stringency scales with infection-control and patient-acuity risk. Designers must verify against the specific adopted edition — values are periodically revised.
These figures are the minimum; project teams routinely design above them for resilience, recovery time, and operational margin. Detailed ach and filtration logic is treated in hvac air change rates filtration, and temperature/humidity control in hvac temperature humidity condensation.
Standard 170 assigns minimum filter efficiencies (MERV ratings) by space category, typically through a two-filter-bank approach in critical areas: