Reaction time and processing speed top the list
When researchers pool workplace studies on high indoor temperatures, the tasks that show up most often as sensitive are the fast, low-level ones: how quickly someone reacts to a signal and how rapidly they can process information [4]. A systematic review of 17 studies found these two skills to be the most consistently affected, while higher cognitive functions like logical and abstract reasoning held up better [4]. That pattern makes practical sense: speed-based tasks depend on alertness and arousal, which heat can nudge, whereas reasoning tasks draw on more deliberate, effortful processing.
The review also points to a temperature band for best performance, generally between 22°C and 24°C, with temperatures above 24°C tending to hurt cognitive performance in work settings [4]. A separate overview of office-like environments reaches the same range, describing performance as optimal between 22°C and 24°C in temperate or cold climates, with both hotter and colder conditions able to degrade performance and learning efficiency [5]. These are broad summaries across many studies, so the range should be read as a general tendency rather than a sharp threshold.
Why controlled chamber studies often find little effect
The strongest-sounding claims come from reviews, but tightly controlled experiments tell a more muted story. In a climate chamber study that tested office workers at 22°C, 25°C, 28°C and 31°C, temperature changes across that range had only minimal effects on memory, math processing, executive function, planning, reasoning, decision-making and motor skills [1]. Task complexity was a much stronger predictor of performance than temperature, and the interaction between temperature and task difficulty was not significant [1]. In other words, harder tasks were harder regardless of how warm the room was.
A companion study using heart-rate variability as a physiological marker of mental workload found a similar pattern. Task type significantly affected the heart-rate measures, while temperature and task complexity had limited influence [2]. The links between heart-rate variability and subjective workload were weak in magnitude, though they grew somewhat stronger at higher temperatures and showed additional significant associations at 31°C [2]. This is consistent with the idea that heat may subtly shift autonomic regulation without producing large, obvious drops in task scores.
Cold rooms and added heating: small or no measurable gains
Temperature effects are not only about heat. In a low-temperature office study at 18°C, adding a personal radiant heating panel did not significantly improve thermal comfort, vigilance, accuracy or reasoning [3]. Slower reaction times appeared in processing-speed and working-memory tasks while the panel was in use, but these effects were small and vanished once differences between participants were accounted for [3]. The authors suggest participants may already have been satisfied at 18°C, so the extra heating had little to work with [3].
This fits the broader concave picture: performance tends to be best in a middle band and can deteriorate at both higher and lower temperatures [5]. It also helps explain why a single cold-room intervention may show nothing: if occupants are comfortable enough, there is little room for a heating panel to improve cognition.
How much weight to give these findings
The most direct evidence for reaction time and processing speed comes from a review whose own authors describe the results as inconsistent and note limited ecological validity, meaning the underlying studies may not fully reflect real workplaces [4]. The chamber experiments, meanwhile, use small samples and short exposures, and their null results apply to the specific temperature range and task set tested [1][3]. Taken together, the evidence suggests that speed-based tasks are the most likely to show heat effects, that reasoning is comparatively robust, and that in many controlled settings the temperature effect on task scores is modest next to the difficulty of the task itself [1][2][4].
Sources used in this answer
The Effect of Indoor Temperature and Task Complexity on the Cognitive Performance of Office Workers
Across 22–31°C in a climate chamber, temperature had minimal effects on office workers' cognitive performance, while task complexity was a stronger predictor and the temperature–difficulty interaction was non-significant.
Heart Rate Variability as a Marker of Cognitive Workload: Influence of Temperature and Task Complexity in Office Settings
Task type significantly affected heart-rate-variability measures of workload, whereas temperature and task complexity had limited influence, with only weak HRV–workload associations that grew slightly stronger at higher temperatures.
Evaluation of Individual Radiant Heating as a Strategy for Maintaining Indoor Thermal Comfort in Low-Temperature Office Environments
A personal radiant heating panel at 18°C did not significantly improve thermal comfort, vigilance, accuracy or reasoning, and small slower reaction times disappeared after accounting for participant-level variability.
[The impact of high indoor temperatures on cognitive performance within the work setting: a systematic review].
In a review of 17 workplace studies, reaction time and processing speed were the cognitive skills most sensitive to elevated indoor temperatures, higher reasoning was more resistant, and optimal functioning was generally around 22–24°C.
Health, work performance, and risk of infection in office-like environments: The role of indoor temperature, air humidity, and ventilation
Cognitive and work performance in offices is optimal between 22°C and 24°C in temperate or cold climates, with both higher and lower temperatures potentially degrading performance.