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Ventilation

ASHRAE 170

ANSI/ASHRAE/ASHE Standard 170 — Ventilation of Health Care Facilities

ASHRAELatest · 170-2025 (supersedes 170-2021)Referenced by FGI Guidelines and by CDC infection-control guidance.

Edition last checked against publisher sources:

Scope

Standard 170 specifies minimum ventilation requirements for hospital, outpatient, and residential health-care spaces. It defines air changes per hour (ACH), pressure relationships, filtration efficiency, and temperature/humidity ranges for every functional space in a hospital, including the patient room and airborne infection isolation room.

Where it applies in the room

  • Total and outdoor air changes per hour by room type
  • Pressure relationship (positive, negative, neutral) versus adjacent spaces
  • Filtration MERV / HEPA requirements
  • Temperature and relative humidity ranges

Key requirements at a glance

Space-by-space tableTotal and outdoor air changes, pressure relationship, filtration, and temperature/humidity are set per space type; values have changed between editions.
AIIR (isolation)≥ 12 ACH new / ≥ 6 existing; negative to corridor by ≥ 0.01 in. w.c. (consistent with CDC's 2003 environmental infection control guideline; confirm against the adopted 170 edition)
Protective environment room≥ 12 ACH; positive to corridor; HEPA-filtered supply. (consistent with CDC's 2003 environmental infection control guideline; confirm against the adopted 170 edition)

Summarized for reference. Consult the source document for the definitive text.

Caveats

  • Authorities having jurisdiction adopt and enforce different editions of Standard 170; confirm which edition applies.

Source & further reading

Also known as

  • ANSI/ASHRAE/ASHE Standard 170
  • ASHRAE Standard 170
  • ASHRAE 170

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Cited in

Guides that reference ASHRAE 170