Healthcare spaces carry the most demanding environmental requirements of any building type — narrow temperature bands, minimum and maximum humidity limits driven by infection control and patient safety, and the constant risk that conditioned air meeting cold or hot surfaces will produce condensation that feeds mold, corrodes equipment, or compromises a sterile field. This Article covers how design, construction, and commissioning teams set, achieve, and maintain temperature and relative humidity (RH) in occupied clinical environments, and how they engineer the building enclosure and mechanical systems to keep moisture under control.

The companion Articles in this Chapter cover the related parameters — the ASHRAE 170 design-parameter table, pressure relationships and airflow direction, and air-change rates and filtration. This article stays in its lane: the thermal and moisture set of requirements, the equipment and enclosure strategies that satisfy them, and the failure modes (most importantly condensation) that result when they are missed.

Why Temperature and Humidity Are Patient-Safety Parameters, Not Comfort Settings

In a hotel or office, temperature and humidity are comfort variables; in a hospital they are clinical and life-safety variables governed by code. The governing framework in the United States is ASHRAE Standard 170, Ventilation of Health Care Facilities, whose space-by-space design parameters are adopted by reference into the FGI Guidelines for Design and Construction of Hospitals / of Outpatient Facilities / of Residential Health, Care, and Support Facilities. Most state health departments and Authorities Having Jurisdiction (AHJs) adopt an FGI edition as enforceable code, which means the ASHRAE 170 temperature and humidity ranges become legal minimums for licensure. CMS Conditions of Participation and accrediting organizations (The Joint Commission, DNV, ACHC**) survey against these conditions, and a sustained out-of-range humidity reading in an operating room or sterile storage area is a citable deficiency.

The reasons these parameters matter clinically include:

• Infection control. Both very low and very high humidity promote risk. Dry air increases airborne particle and droplet-nuclei viability and dispersal; saturated air encourages microbial and fungal growth on surfaces and in materials. The mid-range band (often described as roughly 30–60% RH) is the practical compromise.
• Surgical and patient safety. Excessively dry air in an OR raises electrostatic discharge concerns and dries mucous membranes and exposed tissue; excessively humid air degrades the sterile field and packaging. Temperature affects patient normothermia, surgical-team performance, and equipment behavior.
• Material and device integrity. Sterile supplies, pharmaceuticals, reagents, imaging equipment, and electronics all carry manufacturer environmental limits. Sterile packaging integrity, medication stability, and analyzer calibration all depend on stable conditions.
• Building durability. Uncontrolled moisture is the leading cause of hidden envelope and system damage in hospitals — mold in wall cavities, corrosion in mechanical rooms, and degradation of insulation and finishes.

The practical takeaway: temperature and humidity in clinical spaces are designed to a code-required range, monitored continuously, and documented — not adjusted at a wall thermostat by occupants.

Temperature Design Ranges by Space Type

ASHRAE 170 assigns each healthcare space type a design temperature range rather than a single setpoint, giving clinical staff a band to work within. The ranges reflect the function of the space and the people in it. Typical patterns (consult the current ASHRAE 170 / FGI edition for the controlling numbers for each space):

Two design implications recur across these spaces:

• Surgeon- and clinician-adjustable setpoints. ORs and many procedure rooms are designed so staff can move temperature across a code-allowed band quickly during a case — for example, raising the room for a pediatric or burn patient. The HVAC system, controls, and reheat capacity must be sized to swing temperature within the band without violating humidity or airflow requirements.
• Wide swing capacity demands heating and cooling capacity simultaneously. Achieving a low room temperature while keeping humidity in range almost always requires cooling the air below the desired room temperature to wring out moisture, then reheating it — see the dehumidification discussion below.

Humidity Design Ranges and the Low/High Limits Debate

Humidity is the parameter that most often drives mechanical-system design and the parameter that most often generates field problems. ASHRAE 170 / FGI specify, for each sensitive space, a minimum RH (to limit static and dryness risk) and a maximum RH (to limit microbial growth and protect the sterile field and materials). A widely referenced general band for sensitive clinical spaces is approximately 30% RH minimum to 60% RH maximum, with operating rooms historically having been required at a higher minimum (the long-standing 35% lower limit was relaxed in later code cycles to roughly 20% for some OR conditions, subject to the controlling edition and AHJ). Always design to the specific edition adopted by the project's AHJ — the OR low-humidity limit in particular has changed across editions and is frequently the subject of variance requests.

Key humidity articles the team must hold clearly:

• Relative humidity vs. dew point. RH is temperature-dependent; the same amount of moisture in the air yields different RH readings at different temperatures. Designers control dew point at the air handler (the absolute moisture content) and let room RH follow from room temperature. A space held at a stable dew point will see RH rise as the room cools and fall as it warms — which is why temperature swings in an OR directly move the RH reading.