Which Classrooms Overheat First? What Sensor Data Reveals About a School's Hottest Rooms

The short answer

The classrooms that overheat first are usually south- or west-facing, on the top floor, packed with heat-generating equipment, or in modular buildings with poor ventilation. But every school is different. The only reliable way to find your hottest rooms is to measure temperature room by room, across the whole day.

In Twinview's Too Hot to Learn? study, sensors in 105 teaching spaces across three UK schools found the share of time above 24°C ranged from 10.0% at one school to 20.5% at another. Building age didn't explain the difference.

Which classrooms overheat the most?

Five types of room tend to run hottest:

• South- and west-facing rooms, which take the strongest afternoon sun.
• Top-floor classrooms, which gain heat through the roof.
• ICT suites and science labs, where computers, projectors and equipment add heat.
• Modular and temporary buildings, which often have thin walls and limited ventilation.
• Rooms with windows that stay shut, because of security, noise or restrictors.

What does classroom temperature data show?

Twinview sensors monitored 105 teaching spaces in two large secondary schools and one primary, across 51 teaching days between 20 April and 13 July 2026. The data shows overheating builds in particular places and at particular times:

One in five hours too warm at the worst site. 20.5% of monitored time was above 24°C, against 10.0% at the best.

Afternoons are the danger zone. The share of spaces above 24°C rose more than fourfold, from 5.1% at 09:15 to 23.4% at 15:00.

Hot rooms stay hot. 33.7% of room-days had some time above 24°C, and 18.5% had two hours or more.

Newer isn't always cooler. One recently built school performed best, another recent school performed worst, and the older school sat in between.

Across the sample, 5,062 room-hours were above 24°C, equivalent to around 6,074 fifty-minute lessons. The study uses 24°C as a consistent screening threshold, not the statutory definition of overheating.

Why doesn't one thermostat reading tell you enough?

A single thermostat or a building-wide average hides the problem. Reception can feel comfortable while a top-floor classroom is well above 24°C by mid-afternoon. Staff complaints help, but they arrive after pupils have already lost focus.

Room-level sensors show which rooms overheat, how often and for how long. At the hardest-hit school in the study, 29.3% of spaces were above 24°C by 15:05. That turns a general worry into a ranked list of rooms to act on.

How can schools cool their hottest classrooms?

Adapting isn't mainly about air conditioning. Once you know which rooms are the problem, the report points to five steps:

Stop heat getting in. External shading, solar control and roof treatments work better than blinds behind already-hot glass.

Purge heat overnight. Use secure night or early-morning ventilation, with mechanical purge where natural airflow isn't enough.

Act before rooms heat up. Link alerts and controls to forecasts and occupancy, rather than opening windows once a room is already hot.

Cut internal heat. Switch off idle computers, projectors and equipment.

Target cooling where the data says. Fit efficient cooling in priority rooms, not air conditioning across the whole estate.

Frequently asked questions

• Why are some classrooms hotter than others in the same school? Orientation, floor level, equipment, glazing and ventilation all vary from room to room. Two classrooms on the same corridor can differ by several degrees.
• What time of day do classrooms get hottest? Mid-afternoon. In the Too Hot to Learn? study, the share of classrooms above 24°C rose from 5.1% at 09:15 to 23.4% at 15:00, as sun, occupancy and equipment heat built up.
• How do I find out which of my classrooms overheat? Install temperature sensors in each teaching space and review the data across a full term, including warm weeks.
• Are modular classrooms more likely to overheat? Often, yes. Lightweight construction and limited ventilation mean they heat up quickly and stay warm.
• Are newer school buildings cooler? Not necessarily. In the study, one recently built school performed best and another performed worst, with the older school in between.
• Do the same rooms get too cold in winter? Not always. The rooms that run coldest in winter can be different from the hottest in summer, so year-round, room-level data matters.

Find your hottest rooms

The full Too Hot to Learn? report shares findings from Twinview sensors across 105 teaching spaces in three UK schools. [Download the report] to see where overheating happens, and what your school can do about it.