Operating theatres feel cold for three reasons: the surgical team works under hot lights in gowns, so a cooler room keeps them comfortable and alert; theatres have very high ventilation rates to control infection, which feel like a constant cool breeze; and the temperature is adjustable for the operation in hand, generally between 18°C and 25°C under NHS guidance. NICE says it should be at least 21°C while the patient is exposed.
This guide explains the standards behind theatre temperature, why patient warming changes the picture, and what it takes to keep a theatre's conditions under control.
At a glance
| Question | Short answer |
|---|---|
| Typical theatre temperature range | Set point generally 18°C to 25°C, adjustable by staff (HTM 03-01) |
| Minimum while the patient is exposed | At least 21°C (NICE CG65) |
| Humidity | 35% to 60% in use (HTM 03-01) |
| Air change rate, conventional theatre | At least 22 air changes an hour in the HTM 03-01 design layouts |
| Why it feels cold | Low set points for gowned staff, and fast, filtered airflow |
Why theatres are kept cool
The surgical team
Surgeons and scrub staff wear gowns, gloves, masks and sometimes lead aprons, stand for long periods, and work under bright operating lights. A room that feels cold to a visitor or a patient can feel warm to them. Comfortable staff make fewer mistakes, sweat less onto the sterile field and stay focused through long procedures, which is why theatres are often run at the cooler end of their range.
Infection control and airflow
Theatre ventilation is designed to keep the air around the wound as clean as possible. NHS England's Health Technical Memorandum 03-01, the guidance on specialised ventilation for healthcare premises, sets out how theatres are supplied with large volumes of filtered air to dilute airborne contamination and waste anaesthetic gases, and keeps the theatre at a higher pressure than the corridor so less clean air does not drift in.
Its design layouts for conventional theatres show at least 22 air changes an hour, and ultra-clean ventilation theatres used for joint replacement and similar surgery move far more air over the operating table. All that moving air makes a room feel cooler than the thermometer says.
Temperature set for the procedure
HTM 03-01 says the limits for the room temperature set point are generally between 18°C and 25°C, depending on the application, and that in operating departments the set point is adjustable by the user within a predetermined range. It also says humidity in the operating department should be between 35% and 60% when in use. Some specialist surgery, such as on babies or burns patients, needs the room much warmer.
Keeping the patient warm
A cold theatre is good for the team but risky for the patient. Anaesthesia lowers the body's ability to keep itself warm, and an unconscious patient with exposed skin loses heat quickly. NICE's guidance on preventing hypothermia in adults having surgery says the ambient temperature in theatre should be at least 21°C while the patient is exposed. Once active warming, such as a forced-air warming blanket, is under way, NICE says the ambient temperature can be reduced to allow better working conditions, and that equipment to cool the surgical team should also be considered.
That is why patients often wake up under warming blankets in a room that felt chilly when they went in: the room is set for the team, and the patient is warmed directly.
What it takes to run a theatre's environment
Theatre ventilation is specialist engineering, built and maintained to HTM 03-01. It typically involves:
- Dedicated air handling plant with high-grade filters, heating and cooling coils, and humidity control.
- Room pressure control between the theatre, preparation, anaesthetic and recovery rooms.
- Controls that let staff set the temperature within the agreed range and show temperature, humidity and plant status.
- Regular verification of air change rates, filter condition and pressures, with records.
Chilled water or refrigeration plant behind the air handlers provides the cooling, and it has to cope with the heat from lights, equipment and people on a full list in summer. If cooling capacity falls short, theatres can overheat and operations may be affected.
Other healthcare spaces
Hospitals and clinics also rely on cooling elsewhere: server and equipment rooms, pharmacy and vaccine storage, mortuaries and patient areas. Our guides to medical fridge temperatures and mortuary cold rooms cover two of them, and our commercial air conditioning installation team works on clinics, surgeries and healthcare offices across London.
Questions people ask about cold operating rooms
Why are operating rooms so cold?
To keep gowned staff comfortable under hot lights, and because theatres have very high ventilation rates for infection control, which feel cool. The temperature is adjustable, and NHS guidance puts the usual set point range between 18°C and 25°C.
What temperature is an operating theatre in the UK?
HTM 03-01 says theatre set points are generally between 18°C and 25°C, adjustable by staff. NICE says the room should be at least 21°C while the patient is exposed, which can be lowered once the patient is being actively warmed.
How do they keep patients warm in a cold theatre?
By warming the patient directly, usually with forced-air warming blankets and warmed fluids, and keeping them covered. NICE recommends keeping the theatre at 21°C or more while the patient is exposed and active warming is being set up.
Why is the air in theatre always moving?
Theatres are ventilated with large volumes of filtered air to dilute contamination and anaesthetic gases. HTM 03-01 design layouts show at least 22 air changes an hour for a conventional theatre, and more for ultra-clean ventilation.
What humidity should an operating theatre have?
HTM 03-01 says humidity in the operating department should be between 35% and 60% when in use.
Do operating theatres use air conditioning?
They use specialist ventilation plant with heating, cooling and humidity control, designed to HTM 03-01, rather than ordinary comfort air conditioning. The principle of cooling the supply air is similar, but the filtration, pressures and air change rates are far more demanding.
The short version
Theatres are cool on purpose: for the team under the lights, and because of the fast, clean airflow that protects the wound. The patient is protected separately, with a minimum of 21°C while exposed and active warming. Behind it all sits ventilation and cooling plant built and maintained to NHS standards.
Last updated: 4 November 2026
Written by
Ali Elm
Ali is the Head of Operations at Be Cool Refrigeration with over a decade of hands-on experience in HVAC and commercial refrigeration. He oversees every installation, repair, and maintenance project, making sure the work meets the highest standards. Ali holds full F-Gas certification and has worked across residential, commercial, and industrial refrigeration systems throughout London and the South East. When he is not on site, he writes these guides to help business owners and homeowners understand their cooling systems better.