ASHRAE 170-2025: What Changed for Healthcare Air Filtration
The 12 changes in ANSI/ASHRAE/ASHE Standard 170-2025, what each one means for filters and air cleaning, and how to tell which edition applies to your project.
Quick answer
ANSI/ASHRAE/ASHE Standard 170-2025 is the new edition of Ventilation of Health Care Facilities. ASHE lists 12 significant changes: optional natural ventilation, system-level outdoor air for mixed 170/62.1 systems, updated Class 2 and 3 imaging rooms with a nuclear medicine clarification, outpatient turndown, separation distances and stack heights, new behavioral health spaces, reserve capacity and fuel, a reorganized Section 10 for construction, equivalent alternative filtration test methods, consistent table requirements, bronchoscopy, and FGI 2026 space types. It applies to your project only when your authority having jurisdiction adopts it. The FGI 2026 documents incorporate it in full.
Why this update matters
ASHRAE 170 is the standard engineers, architects and mechanical contractors use to set ventilation rates, pressure relationships and filtration for every hospital space type, from operating rooms and isolation rooms to imaging suites and pharmacy compounding. The 2025 edition, developed by ASHRAE and ASHE, replaces the 2021 edition. It is the baseline that new construction and major renovations will be designed against as states adopt the FGI 2026 documents.
The 12 changes in ASHRAE 170-2025 and what they mean for filtration
The change descriptions below follow ASHE's published list. The right-hand column is our engineering reading of what each change means for air filtration and air-cleaning specifications.
| Change | What the 2025 edition does | What it means for filtration and air cleaning |
|---|---|---|
| 1. Optional natural ventilation | New requirements for when and how natural ventilation may be used. | Where windows or openings serve a space, filtration and pressure control depend on the mechanical system that remains; confirm which spaces qualify. |
| 2. Total outdoor air at the system level | Outdoor air calculated at the system level for systems serving both Standard 170 and Standard 62.1 spaces. | Affects air-handler sizing and therefore filter bank area, face velocity and pressure drop. |
| 3. Class 2 and 3 imaging, nuclear medicine | Updated requirements for Class 2 and Class 3 imaging rooms and associated non-imaging spaces, with clarification for nuclear medicine. | Class 3 imaging already moved to MERV 16 in the 2021 edition. Nuclear medicine exhaust and pressure relationships matter where radioiodine is handled. |
| 4. Outpatient unoccupied turndown | Clarified unoccupied turndown requirements in outpatient spaces. | Turndown changes airflow through filters; confirm pressure relationships are held when airflow is reduced. |
| 5. Separation distances and stack heights | Clarified separation distances and stack discharge heights for complex situations. | Relevant to exhaust from isolation, nuclear medicine and laboratory spaces near outdoor air intakes. |
| 6. Behavioral health | Additional behavioral health space types. | Ligature-resistant, tamper-resistant air devices and filter access need early coordination. |
| 7. Reserve capacity and on-site fuel | Updated cooling and heating reserve capacity and on-site fuel requirements. | Indirect for filtration; affects resilience planning for critical air handlers. |
| 8. Section 10: ventilation during construction | Section 10 reorganized and updated for ventilation during construction. | Temporary filtration, negative pressure containment and protection of outdoor air intakes during renovation work. |
| 9. Alternative filtration test methods | Indication of equivalent acceptable alternative filtration testing requirements. | Helps projects that buy filters rated to test methods other than ASHRAE 52.2 (MERV). Check the exact equivalence in the standard before substituting. |
| 10. Consistent table requirements | Similar requirements for similar space types across the tables. | Fewer inconsistencies between space types when setting filter efficiencies. |
| 11. Bronchoscopy | Clarified bronchoscopy requirements. | Aerosol-generating procedure rooms: check pressure, air change and exhaust requirements. |
| 12. FGI 2026 space types | New space types to coordinate with the Facility Guidelines Institute (FGI) 2026 space types. | Space names in design documents should match FGI 2026 so the correct table row applies. |
Filtration baseline: what carried over from 2021
The largest filtration change came in the 2021 edition, and it still applies:
- Operating rooms, cesarean delivery rooms and Class 3 imaging rooms moved from MERV 14 to MERV 16 final filtration.
- HEPA filters at the air terminals were added for higher-acuity procedures such as orthopedic, transplant, neurosurgery and burn procedures.
- The 2025 edition adds equivalent alternative filtration test methods, which helps projects that source filters rated to test methods other than ASHRAE 52.2.
Nuclear medicine and I-131 therapy rooms
The 2025 edition clarifies nuclear medicine requirements together with Class 2 and 3 imaging. Spaces that handle radioiodine, such as I-131 therapy rooms and radiopharmacy hot labs, sit where two rulebooks meet: Standard 170 for ventilation and pressure, and NRC or Agreement State radiation protection for airborne radioactivity and effluents. In practice this means negative pressure, dedicated or carefully routed exhaust, HEPA plus activated-carbon filtration for radioiodine, and exhaust discharge placed away from outdoor air intakes, which is itself a clarified topic in 2025.
Read our I-131 therapy room ventilation guide, the I-131 half-life and air safety explainer, and see radioiodine carbon and HEPA filters.
Section 10: ventilation during construction
Section 10 was reorganized and updated. Renovations inside occupied hospitals are where airborne contamination risks are highest: dust, Aspergillus spores and disrupted pressure relationships. Plan for these before work starts:
- Negative pressure containment of the work zone relative to adjacent patient areas, with HEPA-filtered exhaust.
- Protection of outdoor air intakes near dust-generating work.
- Pressure monitoring and documented daily checks.
- Filter replacement and inspection of downstream air handlers after the work ends.
Which edition applies to your project?
Publication is not adoption. ASHRAE 170 becomes binding by reference:
- FGI: the FGI 2026 documents incorporate ANSI/ASHRAE/ASHE Standard 170-2025 in full, including issued addenda.
- States: each state adopts an FGI edition on its own timeline. Indiana adopted FGI 2026 on September 2, 2026, for project applications submitted on or after June 1, 2027. Some states lag several cycles.
- Codes: NFPA 99 and the International Mechanical Code also reference Standard 170.
- Existing spaces are generally held to the edition in force when they were built or last substantially renovated.
Confirm with your AHJ
Ask your state health department or authority having jurisdiction which FGI and ASHRAE 170 editions apply to your project before you finalize filter efficiencies and air-handler selections.
How ASHRAE 170-2025 relates to ASHRAE 241
ASHRAE 170 and ASHRAE 241, Control of Infectious Aerosols, are separate standards that can apply to the same hospital. Standard 170 sets baseline ventilation and filtration by space type using air change rates and filter efficiencies. Standard 241 uses an equivalent clean airflow (ECAi) target for infection risk management mode, which can be met with outdoor air, filtration and air cleaning. Evaluate equipment against each standard's own compliance method. Our ASHRAE 241 vs 170 comparison sets them side by side.
ASHRAE 170-2025 filtration project checklist
- Confirm the adopted FGI and ASHRAE 170 editions with the AHJ.
- List every space by its FGI 2026 space type name so the correct table row applies.
- Record the required filter efficiency per space from the tables (for example MERV 7 pre-filter, MERV 14 or MERV 16 final filter, or HEPA at the terminal).
- If filters are rated to a non-ASHRAE 52.2 method, document the equivalence and keep test reports.
- For nuclear medicine and I-131 areas, coordinate 170 pressure and exhaust with radiation-protection requirements (HEPA plus activated carbon).
- Check exhaust discharge locations and stack heights against outdoor air intakes.
- Plan Section 10 construction ventilation: negative pressure, HEPA exhaust, intake protection.
- Check outpatient turndown schedules against pressure relationships.
- Decide whether ASHRAE 241 infection risk management mode also applies.
- Specify filter access, differential pressure gauges and replacement intervals for operations staff.
Download the checklist (PDF)
One page to share with your design team, contractor or infection prevention committee.
How Iodine Air Systems supports ASHRAE 170 projects
I-131 therapy and hot-lab filtration
HEPA plus activated-carbon filtration and exhaust design for radioiodine areas.
Read the guide → IAS-NC700-HIPortable HEPA + iodine air cart
700 CFM HEPA and iodine adsorber cart for radioiodine areas, temporary exhaust and containment work.
View specifications → FILTERSHEPA and carbon replacement filters
HEPA, pre-filters, impregnated carbon and adsorbers, with specifications and prices.
See consumables → HOSPITALCustom hospital air purification
Engineered HEPA and iodine-catalyzed air purification for critical hospital spaces.
Hospital solutions →ASHRAE 170-2025 FAQ
What is ANSI/ASHRAE/ASHE Standard 170-2025?
It is the 2025 edition of Ventilation of Health Care Facilities, developed by ASHRAE and the American Society for Health Care Engineering (ASHE). It sets minimum ventilation, filtration, pressure relationship, temperature and humidity requirements for patient care, resident care and related support areas.
What changed in ASHRAE 170-2025 compared with 170-2021?
ASHE lists twelve significant changes, including optional natural ventilation, system-level outdoor air for mixed 170/62.1 systems, updated Class 2 and 3 imaging requirements with a nuclear medicine clarification, outpatient turndown, separation distances and stack heights, behavioral health space types, reserve capacity, a reorganized Section 10 for construction, equivalent alternative filtration test methods, consistent table requirements, bronchoscopy, and FGI 2026 space types.
Did ASHRAE 170-2025 change MERV requirements?
The big filtration step came in the 2021 edition, which raised operating rooms, cesarean delivery rooms and Class 3 imaging rooms from MERV 14 to MERV 16 and added HEPA at the air terminals for higher-acuity procedures. The 2025 edition adds equivalent alternative filtration test methods and standardizes similar spaces across tables. Check the 2025 tables for each space type on your project.
When does ASHRAE 170-2025 become mandatory?
Only when your authority having jurisdiction adopts it. Standard 170 becomes binding by reference: the FGI documents incorporate it, states adopt FGI, and NFPA 99 and the International Mechanical Code reference it. The FGI 2026 documents incorporate 170-2025 in full. Indiana, for example, adopted FGI 2026 on September 2, 2026 for project applications submitted on or after June 1, 2027.
Does ASHRAE 170-2025 apply to existing hospitals?
Standard 170 applies to new buildings, additions and renovated spaces. Existing areas are usually held to the edition in force when they were built or last substantially renovated, so one hospital can contain spaces designed to several editions.
What does ASHRAE 170-2025 mean for nuclear medicine and I-131 therapy rooms?
The 2025 edition clarifies nuclear medicine requirements alongside Class 2 and 3 imaging. Rooms where radioiodine is handled also fall under NRC or Agreement State radiation-protection requirements, so exhaust, negative pressure, HEPA and activated-carbon filtration are designed to meet both. See our I-131 therapy room ventilation guide.
How does ASHRAE 170-2025 relate to ASHRAE 241?
Standard 170 sets baseline ventilation and filtration by healthcare space type. Standard 241, Control of Infectious Aerosols, uses an equivalent clean airflow (ECAi) target for infection risk management mode. A hospital can apply both; equipment is evaluated against each standard separately.
What does Section 10 of ASHRAE 170-2025 cover?
Section 10 covers ventilation during construction and was reorganized and updated in 2025. In practice this means planning temporary filtration, negative pressure containment and protection of outdoor air intakes while renovation work goes on next to occupied patient areas.
Can Iodine Air Systems supply filtration for an ASHRAE 170-2025 project?
Yes. We supply HEPA and activated-carbon filtration, replacement filters, portable HEPA and iodine air carts for nuclear medicine and I-131 areas, and custom-engineered air purification for hospital spaces. Send your space types, adopted edition and schedule through the form on this page for a quotation.
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Related pages
- Hospital air purification
- ASHRAE 241 vs ASHRAE 170
- ASHRAE 241 guide
- I-131 therapy room ventilation
- I-131 half-life and air safety
- HEPA DOP vs PAO testing
- HEPA and carbon filters
- University lab iodine filtration
- Technical resources
- Contact sales
Sources
- ASHE: ANSI/ASHRAE/ASHE Standard 170-2025, Ventilation of Health Care Facilities
- ANSI Blog: ANSI/ASHRAE/ASHE 170-2025 Ventilation of Health Care Facilities
- HFM Magazine: Changes to health care ventilation requirements
- Indiana adopts the FGI 2026 Guidelines (AeroPG)
- Facility Guidelines Institute (FGI)
- ASHRAE Standard 241, Control of Infectious Aerosols