ICARELIFE — Technical Guide
Is ASHRAE 170 Mandatory Outside the US? AHJ, Edition and Local Code Conflicts
For contractors, MEP engineers and consultants working outside the US. How to check jurisdiction, edition and conflicts with local codes before design freeze.
Quick Answer
- Is ASHRAE 170 mandatory outside the US? Only if an AHJ adopts it or the contract names it.
- Check in this order: AHJ first, contract second, the standard last.
- Use the edition that the AHJ or the contract names, not the newest edition.
- MERV, US HEPA and EN 1822 H-grades are different scales. Do not convert between them.
- Build a compliance matrix before design freeze. Send each conflict to the AHJ in writing.
What We See in Tenders
A recent enquiry from an MEP contractor in Asia shows four gaps. Details are withheld.
No edition named
The requirement reads "we will follow ASHRAE 170". No edition and no authority are named.
Three filtration scales
One package asks for H13/H14 grades, a MERV 14 filter and "99.97 % at 0.3 µm". These are different scales.
Three airflow units
Design data shows m³/h, L/s and CFM side by side.
No owner at the interface
The buyer procures air conditioning and AHU only. The operating room enclosure is supplied under another contract. Compliance across the boundary has no owner.
Each gap is inexpensive to close before design freeze. Sections 03 to 05 show how.
Does ASHRAE 170 Apply Outside the US?
Not by itself. Outside the US, ASHRAE 170 is borrowed, not adopted. It binds a project through only two routes.
- The authority having jurisdiction (AHJ) adopts it.
- The contract names it.
"We follow ASHRAE 170" states intent, not enforcement. Someone still has to decide which edition applies, and someone has to inspect the result.
Order of enquiry: AHJ first, contract second, standard last.
Four ways ASHRAE 170 reaches a project
| Tier | How it reaches the project | What to do |
|---|---|---|
| A | A regulator's guidelines cite it. Example: the Dubai Health Authority Health Facility Guidelines, Part E, Section 2 (HVAC) list ASHRAE 170 as a reference standard, edition 2017. | Read the guideline text and the edition it names. |
| B | No national healthcare ventilation code. Consultants and tender documents cite it. | Read the project specification. It is the evidence. |
| C | A local code exists and ASHRAE 170 is also cited. | Build a compliance matrix and mark every conflict. |
| D | Not known yet. | Ask the AHJ and the client in writing. |
Where to look first
The origin of the tender often indicates which standard family it cites. Use this to decide whom to ask first. It is not a statement of legal status.
| Tender or consultant origin | Standard family often cited |
|---|---|
| US-trained consultants | ASHRAE 170 |
| UK or Commonwealth | HTM 03-01 |
| German or Central European | DIN 1946-4 |
| French | NF S90-351 |
| Chinese national projects | GB 50333 |
Which Edition Applies
Use the edition the AHJ or the contract names. Not the newest edition.
ASHRAE has published editions of Standard 170 in 2008, 2013, 2017, 2021 and 2025. The 2025 edition is described as current by ANSI. Addenda are published between editions. Values and room entries change.
| Change | What moved |
|---|---|
| 2017 edition, addendum p | For operating rooms, filter Bank 1 changed from MERV 7 to MERV 8. Bank 2 stayed at MERV 14. Source: ASHRAE addendum |
| 2017 to 2021 | More granular, function-based approach with more than 80 room types. Air filtration requirements extensively modified. Guidance on unoccupied turndown added. Source: ASHRAE fact sheet |
| 2021 to 2025 | Optional natural ventilation requirements. System-level outdoor air calculation where one system serves both Standard 170 and Standard 62.1 spaces. Equivalent alternative filtration testing, for easier international use. Section 10 (ventilation during construction) restructured. New behavioral health space types. Alignment with FGI 2026. Source: ANSI |
The named edition can be older than the current one
The Dubai Health Authority guideline cited above lists "ASHRAE 170 - Ventilation of Healthcare 2017" in its reference standards table. The page checked shows no document date. Design to the edition the authority names, and confirm it in writing.
Two Traps: Units and Filtration Scales
Two mismatches cause most avoidable errors on international projects: mixed units and mixed filtration scales.
Trap 1: Units
Drawings, specifications and site instruments on one project can use different units. A pressure written in Pa and read on an in. w.g. instrument is a common error. Fix one unit system per project and print the unit in every table header.
| Quantity | Example | Basis |
|---|---|---|
| Pressure | 2.5 Pa = 0.0100 in. w.g. | 1 in. w.g. ≈ 249.1 Pa |
| Airflow | 1,000 m³/h = 277.8 L/s = 588.6 CFM | 1 L/s = 2.11888 CFM |
Trap 2: Filtration scales
MERV, US HEPA and EN 1822 H-grades are separate scales.
| MERV | HEPA (US) | H13 / H14 (Europe) | |
|---|---|---|---|
| Standard | ASHRAE 52.2 | US HEPA definition (IEST-RP-CC001) | EN 1822 / ISO 29463 |
| Scale | MERV 1 to 16 | One threshold | Classes H13, H14 |
| Particle size tested | 0.3 to 10 µm, in three size bands | 0.3 µm | Most penetrating particle size (MPPS) |
| Efficiency | MERV 14: at least 75 % in the 0.3 to 1.0 µm band MERV 16: at least 95 % in the same band | At least 99.97 % | H13: at least 99.95 % H14: at least 99.995 % (overall efficiency) |
- MERV 14 and H13 are not equivalent. MERV 14 is rated at least 75 % in the 0.3 to 1.0 µm band. H13 is rated at least 99.95 % at its test size.
- US HEPA (0.3 µm) and EN 1822 (MPPS) are close but not identical tests.
- HEPA is not part of the MERV scale.
- ISO 14644 classifies room air cleanliness by particle concentration. It does not grade filters.
Ask in the tender
- Which scale is used: MERV, H-class or both?
- Which edition of the standard applies?
- Is HEPA a standard requirement or a project requirement?
Compliance Matrix Before Design Freeze
One room is one row. Put every named standard side by side and mark each conflict.
- List the standards
Every standard named in the tender or by the AHJ.
- Confirm each edition
In writing, from the AHJ or the client.
- List parameters per room
Particle class, ACH, pressure differential, temperature, humidity, filtration grade.
- Compare and mark conflicts
Place the standards side by side. Mark every difference.
- Submit conflicts to the AHJ
In writing. Do not assume the stricter value wins.
- Record the answers
Add them to the commissioning documents.
Add one more column: who is responsible for each parameter. Where the air-handling supplier and the enclosure builder are different parties, the matrix shows who owns each line.
Example rows (illustrative values only)
| Room | Parameter | Standard A | Local code B | Result |
|---|---|---|---|---|
| OR-01 | Total ACH | 20 | 25 | Conflict |
| OR-01 | Outdoor ACH | 4 | 4 | OK |
| OR-01 | Pressure (Pa) | 2.5 | 5 | Conflict |
The values above are examples of the format. They are not requirements of any standard.
What is checked at commissioning
The same physical tests are usually run whichever standard family applies: filter integrity where HEPA filters are installed, measured air change rate, pressure differentials across the cascade, recovery time, temperature, humidity, noise, illumination and electrical safety. The validation report is the evidence. The name of the standard on the drawing is not.
Background: The Standard in Brief
For readers new to the standard. Skip to section 07 if the basics are known.
What it is
ANSI/ASHRAE/ASHE Standard 170, Ventilation of Health Care Facilities, applies to new buildings, additions and certain alterations. It covers patient care areas, resident care areas and related support areas. It establishes design requirements for temperature, humidity, odour control, asepsis and ventilation rates. (ASHRAE fact sheet)
- It sets minimum design requirements for adoption by code-enforcing agencies.
- It is not a design guide.
- Meeting it means meeting a minimum, not reaching a quality target.
How to read it: one room, one row
The core is a room-by-room table. Each row is a space function. Each column is a requirement. Typical columns are:
- Pressure relationship to adjacent areas
- Minimum outdoor air changes per hour
- Minimum total air changes per hour
- Whether all room air is exhausted directly outdoors
- Whether room units may recirculate air
- Unoccupied turndown
- Minimum filter efficiencies
- Design temperature and humidity
Total ACH and outdoor ACH are two separate numbers. The edition in use defines the exact columns. For operating room values and the engineering behind them, see the operating theatre HVAC design guide. For humidity, see the humidity control guide.
Six requirement types
| Type | What it controls |
|---|---|
| Air change | Dilution of contaminants. Total and outdoor rates are separate. |
| Pressure relationship | Direction of airflow between spaces. |
| Filtration | Particle removal, usually in stages. |
| Temperature and humidity | Design band for comfort, static and microbial control. |
| Exhaust and recirculation | Which rooms exhaust all air outdoors and which may use room units. |
| Unoccupied turndown | Whether airflow may be reduced when the room is empty. |
How it is enforced in the US
Trade sources report that FGI Guidelines incorporate Standard 170 and that more than 40 US states have adopted some edition of the FGI Guidelines (Envigilance, Facilitiesnet). State rules vary. Outside the US, none of this applies automatically.
Terms used in this guide
| Term | Meaning |
|---|---|
| AHJ | Authority having jurisdiction. Decides which edition applies and how compliance is proven. |
| ACH | Air changes per hour. |
| MERV | Minimum Efficiency Reporting Value. Filter grading under ASHRAE 52.2. |
| HEPA | High-efficiency particulate air. US definition: at least 99.97 % at 0.3 µm. |
| MPPS | Most penetrating particle size. The test size in EN 1822. |
| H13, H14 | EN 1822 filter classes. |
| FGI | Facility Guidelines Institute. Publishes US healthcare design guidelines. |
| ASHE | American Society for Health Care Engineering. Co-sponsor of Standard 170. |
| ISO 14644 | Cleanroom air cleanliness classification by particle concentration. |
| Unoccupied turndown | Reduced airflow when a room is empty, where the standard allows it. |
| in. w.g. | Inches of water gauge. A pressure unit. 1 in. w.g. ≈ 249.1 Pa. |
Similar Standards Compared
These documents do not cover the same content. Compare scope before comparing numbers.
| Document | Type | Applies to | Covers | Room classification |
|---|---|---|---|---|
| ASHRAE 170 (US) | Minimum design requirements, for adoption by code-enforcing agencies | New buildings, additions and certain alterations. Patient care, resident care and support areas | Ventilation: temperature, humidity, odour control, asepsis, ventilation rates | By room function. More than 80 room types (2021 edition) |
| GB 50333-2013 (China) | National standard | Design, construction and acceptance of clean operating departments, new or reconstructed | Architecture, air conditioning and purification, medical gas, water, electrical, fire, acceptance | See the GB 50333 guide |
| HTM 03-01, 2021 (UK) | Technical guidance | Mainly acute care. Other settings need a risk assessment. Part A covers new installations and major refurbishments | Legal requirements, design, maintenance and operation of specialised ventilation | See the standard text |
| DIN 1946-4:2018 (Germany) | Ventilation standard | Buildings and rooms of health care | Room-class based requirements | Room classes Ia, Ib and II. The hospital hygienist sets the class, using infection statistics |
| NF S90-351:2013 (France) | Requirements for airborne contamination control | Health care institutions | Design, construction and operation of air treatment and air quality control installations | See the standard text |
| EU level | No single standard | Each member state decides | National documents include DIN 1946-4, ÖNORM H 6020 and SWKI VA105-01 | Varies by country |
Four differences that matter
- Subject. ASHRAE 170 covers ventilation only, for all health care room types. GB 50333 covers one department across all building disciplines.
- Type of document. ASHRAE 170 is written for regulators to adopt. HTM 03-01 is guidance that includes legal, design and operation advice. GB 50333 is a national standard.
- Classification logic. ASHRAE 170 classifies by room function. DIN 1946-4 classifies by room class set by the hospital hygienist.
- Europe is not one system. National standards differ, and some member states have none (a preliminary working-group paper).
Common Misconceptions
| Misconception | Fact |
|---|---|
| ASHRAE 170 is a law. | Outside the US it applies only when an AHJ adopts it or a contract names it. |
| The newest edition applies. | The edition named by the AHJ or the contract applies. |
| ASHRAE 170 means HEPA. | The operating room entry in the 2017 edition addendum lists MERV-rated filter banks. HEPA is a separate scale. Check your edition. |
| Meeting 170 means good design. | It sets minimum design requirements. |
| Modular operating rooms follow another standard. | Modular is a delivery method. The AHJ and the contract still decide which standards apply. |
Frequently Asked Questions
No, not by itself. Outside the US, ASHRAE 170 has no legal force of its own. It applies when an authority having jurisdiction (AHJ) adopts it or when the contract names it. Check the AHJ first, the contract second and the standard last.
List both values side by side in a compliance matrix, room by room. The stricter value is often chosen, but this should not be assumed. Submit each conflict to the AHJ in writing and record the answer in the commissioning documents.
Specify one healthcare ventilation standard family, such as ASHRAE 170, DIN 1946-4 or HTM 03-01, and confirm the choice with the AHJ and the client before design freeze. ISO 14644 can be added to classify room cleanliness, but it does not set ventilation rates.
Follow the edition named by the AHJ or the contract, not the newest edition. Values change between editions and addenda. If a tender names no edition, ask for it in writing before design freeze.
No. MERV is graded under ASHRAE 52.2 across particle size bands from 0.3 to 10 µm. H13 and H14 are graded under EN 1822 at the most penetrating particle size. The scales are different and should not be converted.
Standards and References
Last verified: 25 October 2026. Standards are published in editions and addenda. Check the edition your AHJ adopted.
Primary and official sources
- ASHRAE: Standard 170-2021 fact sheet. Scope and changes from 2017.
- ASHRAE: Standard 170-2017, Addendum p. Operating room filter banks.
- ANSI Blog: ANSI/ASHRAE/ASHE 170-2025. 2025 changes.
- Dubai Health Authority: Health Facility Guidelines, Part E, Section 2 (Mechanical HVAC). References to ASHRAE 170.
- US EPA: What is a MERV rating?
- US EPA: What is a HEPA filter?
- NHS England: HTM 03-01, Specialised ventilation for healthcare premises
- AFNOR: NF S90-351. Title and scope description.
Secondary sources (check against the official text)
- Terra Universal: IEST and EN HEPA classifications. H13/H14 values, IEST definition.
- Camfil: EN 1822 and ISO 29463. MPPS testing.
- Normec: DIN 1946-4 room classes
- chinesestandard.net: GB 50333 and gongbiaoku: GB 50333-2013. Scope and chapter list.
- TNO working paper on European national standards. Preliminary.
- Envigilance: FGI Guidelines and Facilitiesnet: Standard 170 in the FGI Guidelines (2009).
ICARELIFE — Modular Operating Rooms
Send the tender specification
Send the tender specification or the list of named standards. The standards, editions and room parameters can be organised into a compliance matrix before design freeze. A blank matrix template is also available on request.
