Part 1 General

Part 2 Outpatient Facility Types

ANSI/ASHRAE/ASHE Standard 170-2017 Ventilation of Health Care Facilities

Heads up: There are no amended sections in this chapter.
Air-handling and distribution systems are required to provide health care facilities not only with a comfortable environment but also with ventilation to dilute and remove contaminants, provide conditioned air, and assist in controlling the transmission of airborne infection. In order to meet these requirements, air-handling and distribution systems shall be designed according to the requirements of this standard.
The space ventilation and pressure relationship requirements of Tables 7.1, 8.1, and 9.1 shall be maintained for the following spaces, even in the event of loss of normal electrical power:
  1. AII rooms
  2. PE rooms
  3. Operating rooms (ORs), including delivery rooms (Caesarean)
Informative Note: For further information, see NFPA (2015) in Appendix B.
Provide heat sources and essential accessories in number and arrangement sufficient to accommodate the facility needs (reserve capacity), even when any one of the heat sources or essential accessories is not operating due to a breakdown or routine maintenance. The capacity of the remaining source or sources shall be sufficient to provide for domestic hot water, sterilization, and dietary purposes and to provide heating for operating, delivery, birthing, labor, recovery, emergency, intensive care, nursery, and inpatient rooms. Fuel sufficient to support the owner's facility operation plan upon loss of fuel service shall be provided on site.
Exception to 6.1.2.1: Reserve capacity is not required if the ASHRAE 99% heating dry-bulb temperature for the facility is greater than or equal to 25°F (—4°C).
For central cooling systems greater than 400 tons (1407 kW) peak cooling load, the number and arrangement of cooling sources and essential accessories shall be sufficient to support the owner's facility operation plan upon a breakdown or routine maintenance of any one of the cooling sources.
The casing of the AHU shall be designed to prevent water intrusion, resist corrosion, and permit access for inspection and maintenance. All airstream surfaces of AHUs shall comply with ANSI/ASHRAE Standard 62.1, Section 5.41.
Outdoor air intakes for AHUs shall be located a minimum of 25 ft (8 m) from cooling towers and all exhaust and vent discharges. Outdoor air intakes shall be located such that the bottom of the air intake is at least 6 ft (2 m) above grade. New facilities with moderate-to-high risk of natural or man-made extraordinary incidents shall locate air intakes away from public access. All intakes shall be designed to prevent the entrainment of wind-driven rain, shall contain features for draining away precipitation, and shall be equipped with a birdscreen of mesh no smaller than 0.5 in. (13 mm).
Exception to 6.3.1.1: For gas-fired, packaged rooftop units, the separation distance of the unit's outdoor air intake from its flue may be less than 25 ft (8 m). The separation distance shall be greater than or equal to the distance prescribed in ANSI/ASHRAE Standard 62.1, Table 5-1, "Air Intake Minimum Separation Distance1.
Relief air is exempt from the 25 ft (8 m) separation requirement. Relief air is defined as the Class 1 air that could be returned to the air-handling unit from the occupied spaces but is being discharged to the outdoors to maintain building pressurization (such as during air-side economizer operation).
Informative Note: For more information, see ASHRAE Standard 62.1 (ASHRAE 2016a) in Appendix B.
Intakes on top of buildings shall be located with the bottom of the air intake a minimum of 3 ft (1 m) above roof level.
In the case of an areaway, the bottom of the air intake opening shall be at least 6 ft (2 m) above grade. The bottom of the air intake opening from the areaway into the building shall be at least 3 ft (1 m) above the bottom of the areaway.
Informative Note: See Appendix A, Figure A3.
Exhaust discharge outlets that discharge air from AII rooms, bronchoscopy and sputum collection and pentamidine administration rooms, emergency department public waiting areas, nuclear medicine hot labs, radiology waiting rooms programmed to hold patients who are waiting for chest x-rays for diagnosis of respiratory disease, pharmacy hazardous-drug exhausted enclosures, and laboratory work area chemical fume hoods shall
  1. be designed so that all ductwork within the building is under negative pressure;
    Exception to 6.3.2.1(a): Ductwork located within mechanical equipment rooms. Positive-pressure exhaust ductwork located within mechanical equipment rooms shall be sealed in accordance with SMACNA duct leakage Seal Class A2.
  2. be located such that they reduce the potential for the recirculation of exhausted air back into the building.
  1. Exhaust discharge outlets from AII rooms, bronchoscopy and sputum collection exhaust, pharmacy hazardous-drug exhausted enclosures, and laboratory work area chemical fume hoods shall additionally be arranged to discharge to the atmosphere in a vertical direction (with no rain cap or other device to impede the vertical momentum) and at least 10 ft (3 m) above the adjoining roof level.
  2. Exhaust discharge outlets from laboratory work area chemical fume hoods shall discharge with a stack velocity of at least 2500 fpm (1180 L/s).
  3. Exhaust discharge outlets from AII rooms, bronchoscopy and sputum collection exhaust, and laboratory work area chemical fume hoods shall be located not less than 25 ft (8 m) horizontally from outdoor air intakes, openable windows/doors, and areas that are normally accessible to the public.
Exception to 6.3.2.2(c): If permitted by the AHJ, an alternate location (Informative Note: e.g., located adjacent to an air intake but with the exhaust discharge point above the top of the air intake) may be used. The submitted reentrainment analysis shall demonstrate that an exhaust discharge outlet located at a distance less than 25 ft (8 m) horizontally provides a lower concentration of reentrainment than all the areas located at a distance greater than 25 ft (8 m) horizontally on the roof level where the exhaust discharge is located.
Filter banks shall be provided in accordance with Table 6.4. Each filter bank with an efficiency of greater than MERV 12 shall be provided with an installed manometer or differential pressure measuring device that is readily accessible and provides a reading of differential static pressure across the filter to indicate when the filter needs to be changed. All of the air provided to a space shall be filtered in accordance with Table 6.4, except as otherwise indicated in Sections 7.1, 8.1, and 9.1 for spaces that allow recirculating HVAC room units.
Informative Note: For more information, see CDC (2003) in Appendix B.
Table 6.4 Minimum Filter Efficiencies
Space Designation (According to Function) Filter Bank No. 1
(MERV)a
Filter Bank No. 2
(MERV)a
Operating rooms (ORs); inpatient and ambulatory diagnostic and therapeutic radiology; inpatient delivery and recovery spaces 7 14
Inpatient care, treatment, and diagnosis, and those spaces providing direct service or clean supplies and clean processing (except as noted below);
AII (rooms)
7 14
Protective environment (PE) rooms 7 HEPAc,d
Laboratory work areas, procedure rooms, and associated semi-restricted spaces 13b NR
Administrative; bulk storage; soiled holding spaces; food preparation spaces; and laundries 7 NR
All other outpatient spaces 7 NR
Nursing facilities 13 NR
Psychiatric hospitals 7 NR
Resident care, treatment, and support areas in inpatient hospice facilities 13 NR
Resident care, treatment, and support areas in assisted living facilities 7 NR
NR = not required
  1. Informative Note: The minimum efficiency reporting value (MERV) is based on the method of testing described in ANSI/ASHRAE Standard 52.2 (ASHRAE [2017a]).
  2. Additional prefilters may be used to reduce maintenance for filters with efficiencies higher than MERV 7.
  3. As an alternative, MERV-14 rated filters may be used in Filter Bank No. 2 if a tertiary terminal HEPA filter is provided for these spaces.
  4. Informative Note: High-efficiency particulate air (HEPA) filters are those filters that remove at least 99.97% of 0.3 micron-sized particles at the rated flow in accordance with the testing methods of IEST RP-CC001.6 (IEST [2016]).
Filter Bank No. 1 shall be placed upstream of the heating and cooling coils such that all mixed air is filtered.
Filter Bank No. 2 shall be installed downstream of all wet-air cooling coils and the supply fan. All second filter banks shall have sealing interface surfaces.
Filter-bank blank-off panels shall be permanently attached to the filter-bank frame, constructed of rigid materials, and have sealing surfaces equal to or greater than the filter media installed within the filter-bank frame.
Filter frames shall be durable and proportioned to provide an airtight fit with the enclosing ductwork. All joints between filter segments and enclosing ductwork shall have gaskets or seals to provide a positive seal against air leakage.
Cooling coils and drain pans shall comply with the requirements of ANSI/ASHRAE Standard 62.11.
If radiant cooling panels are used, the chilled-water temperature shall always remain above the dew-point temperature of the space.
If radiant heating is provided for an AII room, a protective environment room, a wound intensive care unit (burn unit), an OR, or a procedure room, either flat and smooth radiant ceiling or wall panels with exposed cleanable surfaces or radiant floor heating shall be used. Gravity-type heating or cooling units, such as radiators or convectors, shall not be used in ORs and other special care areas.
Cooling towers shall be located so that drift is directed away from AHU intakes. They shall meet the requirements of Section 6.3.2.
When outdoor humidity and internal moisture sources are not sufficient to meet the requirements of Tables 7.1, 8.1, or 9.1, humidification shall be provided by means of the facility air-handling systems. Steam or adiabatic high-pressure water-atomizing humidifiers shall be used.
  1. Locate humidifiers within AHUs or ductwork to avoid moisture accumulation in downstream components, including filters and insulation.
  2. A humidity sensor shall be provided, located at a suitable distance downstream from the injection source.
  3. Controls shall be provided to limit duct humidity to a maximum value of 90% rh when the humidifier is operating.
  4. Duct takeoffs shall not be located within the humidifier's absorption distance.
  5. Humidifier control valves shall be designed so that they remain off whenever the AHU unit is not in operation.
Chemical additives used in the steam systems that serve humidifiers shall comply with FDA requirements3.
  1. Humidifier water shall be treated with a reverse osmosis process, a UV-C sterilization light source, and a submicron filter. Informative Note: For more information, see ASTM (2011) in Appendix B.
  2. Treated humidifier water shall be continuously circulated from the source to the humidifier valves. All valves, headers, and piping not part of the recirculation loop shall drain completely when not in use.
  3. Ports suitable for testing water quality shall be provided in the treated humidifier water piping system.
  4. Moisture eliminators shall be provided as required to prevent moisture accumulation in ductwork.
Maintain the pressure relationships required in Tables 7.1, 8.1, and 9.1 in all modes of HVAC system operation, except as noted in the tables. Spaces that have required pressure relationships shall be served by fully ducted return systems or fully ducted exhaust systems. The following additional surgery and critical-care patient care areas that do not require a pressure relationship to adjacent areas shall also be served by fully ducted return or exhaust systems: recovery rooms, critical and intensive care areas, intermediate care areas, and wound intensive care units (burn units). In inpatient facilities, patient care areas shall use ducted systems for return and exhaust air. Where space pressure relationships are required, the air distribution system design shall maintain them, taking into account recommended maximum filter loading, heating-season lower airflow operation, and cooling-season higher airflow operation. Airstream surfaces of the air distribution system downstream of Filter Bank No. 2, shall comply with ANSI/ASHRAE Standard 62.1, Section 5.41. The air distribution system shall be provided with access doors, panels, or other means to allow convenient access for inspection and cleaning.
All air distribution devices shall meet the following requirements:
  1. Surfaces of air distribution devices shall be suitable for cleaning. Supply air outlets in accordance with Table 6.7.2 shall be used.
  2. The supply diffusers in ORs shall be designed and installed to allow for internal cleaning.
  3. Psychiatric, seclusion, and holding patient rooms shall be designed with security diffusers, grilles, and registers.
Table 6.7.2 Supply Air Outlets
Space Designation (According to Function) Supply Air Outlet Classificationa
Operating rooms (ORs)b, procedure rooms Supply diffusers within the primary supply diffuser array: Group E, nonaspirating
Additional supply diffusers within the room: Group E
Protective environment (PE) rooms Group E, nonaspirating
Wound intensive care units (burn units) Group E, nonaspirating
Trauma rooms (crisis or shock) Group E, nonaspirating
AII rooms Group A or Group E
Single-bed patient roomsc Group A, Group D, or Group E
All other patient care spaces Group A or Group E
All other spaces No requirement
  1. Informative Note: Refer to the 2017 ASHRAE Handbook-Fundamentals, Chapter 20 (ASHRAE [2017c]), for definitions related to outlet classification and performance.
  2. Surgeons may require alternate air distribution systems for some specialized surgeries. Such systems shall be considered acceptable if they meet or exceed the requirements of this standard.
  3. Air distribution systems using Group D diffusers shall meet the following requirements:
    1. The system shall be designed according to "Design Guidelines" in System Performance Evaluation and Design Guidelines for Displacement Ventilation, Chapter 74.
    2. The supply diffuser shall be located where it cannot be permanently blocked (Informative Note: e.g., opposite the foot of the bed).
    3. The room return/exhaust grille shall be located in the ceiling, approximately above the head of the patient bed.
    4. The transfer grille to the toilet room shall be located above the occupied zone.
Where smoke barriers are required, heating, ventilating, and air-conditioning zones shall be coordinated with compartmentation to minimize ductwork penetrations of fire and smoke barriers.
  1. Maintenance access shall be provided at all dampers.
  2. All damper locations shall be shown on design drawings.
  3. Air-handling systems shall be arranged such that damper activation will not damage ducts.
Ducts that penetrate construction intended to protect against x-ray, magnetic, radio frequency interference (RFI), or other radiation shall not impair the effectiveness of the protection, nor shall the treatment of these penetrations impair the ventilation of the space served.
Energy recovery systems shall be located upstream of Filter Bank No. 2. If energy recovery systems are used, the systems shall not allow for any amount of cross-contamination of exhaust air back to the supply airstream via purge, leakage, carryover, or transfer except as allowed in Section 6.8.3.
Airborne infectious isolation room exhaust systems serving AII rooms or combination AII/PE rooms shall not be used for energy recovery.
Exception to 6.8.2: Airborne infectious isolation room exhaust systems serving AII rooms or combination AII/PE rooms may be served by an energy recovery system where the supply airstream components and the exhaust airstream components are fully separated by an air gap of adequate distance to prevent cross-contamination that is open to the atmosphere (e.g., run-around pumped coils).
If energy recovery systems with leakage potential are used, they shall be arranged to minimize the potential to transfer exhaust air directly back into the supply airstream. Energy recovery systems with leakage potential shall be designed to have no more than 5% of the total supply airstream consisting of exhaust air. Energy recovery systems with leakage potential shall not be used from these exhaust airstream sources: emergency department waiting rooms, triage, emergency department decontamination, radiology waiting rooms, darkroom, bronchoscopy sputum collection and pentamidine administration, laboratory fume hood and other directly ducted laboratory equipment exhaust, waste anesthesia gas disposal, autopsy, nonrefrigerated body holding, endoscope cleaning, central medical and surgical supply soiled or decontamination room, laundry general, hazardous material storage, dialyzer reprocessing room, nuclear medicine hot lab, nuclear medicine treatment room, and any other space identified by the AHJ or the infection control risk assessment (ICRA) team.
  1. An exterior vapor barrier shall be provided for insulation on cold surfaces. A vapor barrier is not required for insulation materials that do not absorb or transmit moisture.
  2. Existing insulation and duct lining accessible during a renovation project shall be inspected, repaired, and/or replaced as appropriate.
  3. Duct lining shall not be used in ductwork located down-stream of Filter Bank No. 2. Duct lining with an impervious cover may be allowed in terminal units, sound attenuators, and air distribution devices downstream of Filter Bank No. 2. This lining and cover shall be factory installed.
  4. Duct lining shall not be installed within 15 ft (4.57 m) downstream of humidifiers.
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