Clinic ventilation and filtration in NYC and Long Island
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Summary
In New York City the Mechanical Code does not send outpatient clinics to ASHRAE 170 for ventilation rates, so the owner and the engineer choose the design basis: code minimums, ASHRAE 170 as a voluntary standard, or a stricter basis required by an Article 28 license or a payer. That choice sets fan capacity, filter grade and pressure relationships. A clinic that wants better filtration needs equipment selected for it, filters staff can reach, and a waiting room exhausted slightly more than it is supplied, so air moves from the clinical rooms toward it.
What the codes require
Section 407.1 of the 2022 NYC Mechanical Code (opens an external site) states that mechanical ventilation for ambulatory care facilities (Group B) and Group I-2 occupancies shall be designed and installed in accordance with all applicable federal, state and local regulations. The model International Mechanical Code sends these occupancies to ASHRAE 170; New York City rewrote the section. Table 403.3 has no row for exam rooms. It lists reception areas, booking and waiting, office spaces, and a pharmacy preparation area at 5 cfm per person plus 0.18 cfm per square foot, with a default of 10 people per 1,000 square feet. The city code refers to ASHRAE 170 only for outdoor air intakes in Group I occupancies (MC 401).
On Long Island, the 2025 New York State Uniform Code took effect December 31, 2025. The model mechanical code behind it refers ambulatory care to ASHRAE 170, and whether the state text keeps that reference is for the engineer to confirm on each project. Article 28 facilities are a third case: 10 NYCRR 711.2 references the FGI Guidelines (opens an external site), and the edition the Department of Health currently applies should be confirmed with the department. FGI's 2026 editions are scheduled for release in fall 2026.
| Basis | Where it applies | What it sets |
|---|---|---|
| NYC Mechanical Code Table 403.3 | The minimum for outpatient clinics in New York City | Outdoor air per person and per square foot for reception, waiting, office and pharmacy preparation; no exam room row |
| ASHRAE 170, 2025 edition | Voluntary in NYC clinics; referenced by the model code outside the city; applied through FGI for Article 28 | Outdoor and total air changes, pressure relationships and filtration by room type, with outpatient spaces in their own section |
| ASHRAE 241, 2023 | Voluntary, for an infection risk management mode | Equivalent clean airflow, counting filtration and air cleaners only when tested and installed to the standard |
| CDC and NIOSH clean air target | Guidance, which CDC calls a rough guide | Five or more air changes per hour of clean air in occupied rooms |
ASHE notes that authorities having jurisdiction enforce different editions of ASHRAE 170 (opens an external site), and room values have changed between editions, so the design should name the edition and the table it uses for each room.
Waiting rooms, isolation rooms and pressure
CDC's isolation guideline (opens an external site) calls for respiratory hygiene at the first point of encounter: signs in the languages patients read, masks for coughing patients and, in common waiting areas, spatial separation of ideally more than 3 feet when possible. In physician offices without an airborne infection isolation room, a patient with a suspected airborne infection is masked and placed in a private exam room with the door closed until transfer.
For the floor plan, this means a separate waiting zone near the entrance, and one exam room near the entrance that can serve as the isolation room, with the option of dedicated exhaust.
Air should move from clean areas toward less clean ones. Supply serves the clinical rooms and the waiting room, which still needs its outdoor air, and the waiting room and toilet rooms are exhausted slightly more than they are supplied, so the waiting room runs slightly negative to the clinical corridor, with transfer grilles and door undercuts sized for the airflow. A true negative-pressure exam room needs a dedicated exhaust fan, discharge to the outdoors and a pressure monitor. Exhaust outlets must keep code distances from intakes and lot lines (MC 401.4 and 501), so a room at the street front may need a long duct run. Without a balance report and periodic checks, negative pressure is only a note on a drawing, since propped doors and loaded filters change it.
MERV 13, HEPA and filter access
EPA advises upgrading HVAC filters to the highest efficiency (opens an external site) the system can accommodate, with review by an HVAC professional, and MERV 13 is the common target. A MERV 13 filter dropped into a 1-inch rack on a small packaged unit can cut airflow and freeze the coil. The fan and rack must be selected for the filter, usually a 4-inch media cabinet with a sealed rack so air cannot bypass it.
HEPA filtration in a central system needs far more static pressure, a stronger fan and a sealed housing, and it is rarely practical in a rooftop unit. Where the owner wants HEPA-grade air in the waiting room or the isolation room, portable HEPA units sized by clean air delivery rate (opens an external site) are the realistic option. When new equipment is going in, an air handler large enough to take higher-efficiency filtration costs less than replacing an undersized unit later, and two smaller units in place of one keep part of the suite running when one fails.
Filters that staff cannot reach are not changed on schedule. We plan units with side-access filter doors, return grilles at reachable heights, no equipment above exam tables, access panels outside clinical rooms where the layout allows, and a differential pressure gauge on the filter bank. Landlord base-building systems may not permit tenants to change filters or outdoor air rates, which the lease should address.
UV-C claims and questions for an HVAC proposal
Upper-room ultraviolet germicidal irradiation has a CDC and NIOSH basis in tuberculosis settings, as a supplement to ventilation and other controls. In-duct UV, ionization and plasma devices vary widely. Before accepting one, ask the vendor for independent test data, evidence that the device does not produce ozone, and its maintenance requirements. We install the air-cleaning equipment the engineer specifies and make no claims about its effect on infection.
When comparing HVAC proposals for a clinic, ask each proposer for the following.
- The design basis used, including the edition of any standard
- Outdoor air and total airflow for each room
- Filter grade, rack depth and fan static pressure with loaded filters
- The intended pressure relationship for each room and how it will be verified
- Where filters are accessed and the expected change interval
- What the suite loses when one unit fails
Frequently asked questions
Does a medical office in NYC have to follow ASHRAE 170?
Not through the city's Mechanical Code for an ordinary outpatient clinic. MC 407.1 requires ambulatory care ventilation to meet applicable federal, state and local regulations, and Table 403.3 sets the outdoor air minimums. ASHRAE 170 can still apply through an Article 28 license, a payer requirement or the owner's choice, and the engineer of record sets the basis.
Is MERV 13 or HEPA better for a clinic?
HEPA captures more particles, but in a central system it needs a fan and housing designed for the added resistance. MERV 13 in a properly sized media rack is the practical central upgrade, supplemented by portable HEPA units in the waiting room or isolation room.
Can a small clinic have a negative-pressure exam room?
Yes, with a dedicated exhaust fan, outdoor discharge at a permitted location, tight construction and a pressure monitor. Where there is no such room, CDC's approach for physician offices is to mask the patient and use a private exam room with the door closed.
Do UV lights in the air conditioning system disinfect a clinic?
Results depend on the device and how it is installed, and an in-duct lamp acts only on the air and surfaces it reaches. Ask for independent test data and ozone information, and treat any device as a supplement to ventilation and filtration rather than a substitute.
Sources
- 2022 NYC Mechanical Code, Chapter 4: Ventilation (opens an external site)NYC Department of Buildings
- ANSI/ASHRAE/ASHE Standard 170-2025, Ventilation of Health Care Facilities (opens an external site)American Society for Health Care Engineering
- III. Precautions to Prevent Transmission of Infectious Agents (opens an external site)Centers for Disease Control and Prevention
- How Much Ventilation Is Enough? (opens an external site)CDC, National Institute for Occupational Safety and Health
- Air Cleaners, HVAC Filters, and Respiratory Viruses (opens an external site)U.S. Environmental Protection Agency
- The FGI Code/Guidelines documents (opens an external site)Facility Guidelines Institute
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