What filtration level does ASHRAE 170 require for surgical suites?
ASHRAE 170-2021 requires MERV-16 final filtration for operating rooms (Class B/C surgery), with MERV-14 for procedure rooms and trauma rooms. Systems use two filter banks in series: a prefilter (typically MERV-7/8) upstream of coils and the final filter bank downstream. Earlier editions specified MERV-14 for ORs — confirm which edition your AHJ enforces before designing or replacing.
The filtration chain
- Filter Bank 1 (prefilter): MERV-7 or higher, upstream of heating/cooling coils — protects the coils.
- Filter Bank 2 (final): MERV-16 for ORs, MERV-14 for procedure rooms — downstream of coils and supply fan, the patient-protection layer.
- Seal the edges: filter bypass around poorly seated filters defeats the rating — gasket and seal filter racks.
- HEPA is not generally required by 170 for ORs (MERV-16 suffices), though some facilities specify it; protective environment (PE) rooms for transplant/burn patients have their own HEPA requirements.
Maintenance is the requirement too
The standard’s filtration levels assume maintained filters: pressure drop monitored, changeout on schedule or differential pressure, not on the calendar alone. A loaded MERV-16 performing at MERV-8 pressure drop is still filtering — but verify airflow is maintained, since loaded filters reduce ACH.
The rating is only as good as the seal around the filter.
See OR vs. procedure room ventilation and HEPA filtration in construction.
FAQ
What MERV rating do operating rooms require?
MERV-16 final filtration under ASHRAE 170-2021 (MERV-14 under earlier editions — verify your adopted edition).
Do operating rooms require HEPA filters?
Not generally under ASHRAE 170 — MERV-16 final filtration is the requirement; some facilities specify HEPA voluntarily.
Why two filter banks?
The prefilter protects coils; the final bank downstream of coils and fan protects patients. Both must be sealed against bypass.