Does keeping people thermally comfortable at higher indoor temperatures still reduce their cognitive performance?

Why reaction speed suffers before complex reasoning

When the indoor temperature rises, the brain's ability to respond quickly appears to degrade before its ability to reason through a complex problem. A systematic review of 17 workplace studies found that reaction time and processing speed were the cognitive skills most consistently affected by elevated temperatures, while higher functions such as logical and abstract reasoning were more resistant [2]. This pattern suggests that heat may tax basic attentional and motor-response processes more than deliberate, effortful thinking.

That distinction matters for anyone trying to judge whether comfort is enough. A person may feel thermally comfortable and still show slower responses on a timed task. In a controlled chamber study with 71 university students, raising the temperature from 23°C to 28°C significantly reduced task accuracy, with an average error increase of 5.2% in six of ten tasks under high VOC conditions, but there was no clear evidence that temperature affected reaction speed [5]. The direction of the effect can therefore depend on which cognitive measure is used and what else is in the air.

Where the temperature threshold sits

The most commonly cited range for optimal cognitive functioning is roughly 22°C to 24°C. The same systematic review concluded that temperatures above 24°C can negatively affect cognitive performance in work settings [2]. A study of female students in Saudi Arabia found benefits for speed and accuracy when indoor temperature was set between 20°C and 23°C, compared with higher temperatures and poorer ventilation [1].

These ranges come with important scope limits. The Saudi study involved short-term exposures lasting no more than two hours, so it does not tell us what happens across a full workday [1]. The systematic review noted that the included studies had limited ecological validity, meaning they may not fully reflect real workplaces, and that unequivocal conclusions remain difficult [2]. The threshold is therefore a useful guide rather than a sharp cliff.

Comfort is not the same as peak performance

Feeling thermally comfortable at a higher temperature does not guarantee that cognitive performance is unaffected. The Saudi study found that both ventilation and thermal environmental control mattered for optimal learning conditions, not temperature alone [1]. In the chamber study, higher temperatures also led to worse perceived air quality and symptoms such as eye irritation and fatigue, even as the temperature effect on accuracy was measured separately from comfort votes [5].

A full-day multitask study adds a further caution. Sixteen participants completed eight sessions across a 7-hour-20-minute protocol at four nominal temperatures. The researchers found that temporal patterns differed more consistently among tasks than among temperature conditions, and no temperature-by-duration interaction was detected for any task, meaning the nominal temperatures did not modify full-day performance trajectories [3]. Several tasks had their highest descriptive mean performance at 18°C, but the authors explicitly noted this boundary observation did not establish a cognitive optimum [3]. In other words, the temperature that feels comfortable may not be the temperature at which every task is performed best.

What this means for real rooms and real work

For practical purposes, the evidence supports keeping indoor temperatures below about 24°C when speed and accuracy matter, and not assuming that thermal comfort at higher temperatures is sufficient protection. The effect is most likely to show up in tasks that require fast reactions or sustained attention rather than in complex reasoning [2]. Ventilation should be considered alongside temperature, since the Saudi study found benefits from combining moderate temperature with low CO2 levels [1].

The evidence is less clear about prolonged exposure. The full-day study found that task type and time of day shaped performance more consistently than temperature did, and its significant pairwise differences were limited to selected task-session combinations [3]. The chamber study found accuracy effects at 28°C but no clear reaction-speed effect, and no interaction between temperature and VOC levels [5]. Taken together, these results suggest that higher indoor temperatures can impair some aspects of cognitive performance even when people are thermally comfortable, but the size and consistency of the effect depend on the task, the duration, and other indoor conditions.

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