Feeling fine is not the same as performing fine
The core reason this question is interesting is that comfort and cognition are measured through different channels. Comfort is a subjective rating — a person says whether the room feels too warm, too cold, or just right. Cognitive performance is an objective score on tasks such as vigilance or short-term memory. A study of office workers exposed to different temperatures and air movement collected subjective thermal comfort and perceived air quality alongside physiological responses and cognitive performance, which is exactly the combination needed to see whether the two tracks separate [1].
A separate laboratory study of healthcare workers kept the temperature fixed at 25°C and varied carbon dioxide instead. Even there, higher CO2 (1800 ppm versus 1100 ppm) was associated with a thermal dissatisfaction score about 0.88 units higher and a heart rate about 9 beats per minute higher, and the analysis reported significant effects involving cognitive performance and CO2 on thermal comfort [3]. That study does not test raised temperature, so it cannot answer the temperature question directly, but it shows that air-quality conditions can shift how people feel and perform without a temperature change — a reminder that 'comfortable' and 'performing well' are separate outcomes.
The broader evidence points the same direction, with caveats
A systematic review of indoor environmental quality in higher-education spaces found that thermal comfort and indoor air quality showed the strongest and most consistent associations with academic performance, with uncomfortable temperatures and high CO2 linked to reduced concentration, cognitive fatigue, and lower test scores [5]. That review is about uncomfortable conditions rather than moderately raised ones, and it notes heavy reliance on cross-sectional designs and subjective data, so it supports the general link between thermal conditions and cognition without settling the 'comfortable but warm' case.
A review of personalized environmental control systems found that evidence for benefits to human performance, including cognitive function, is sparse but promising, and that performance metrics are inconsistent across studies [2]. This matters for the reader's question because it means the absence of a clear performance drop in any single comfortable-warm study would not prove there is none — the measurement tools and study designs vary too much.
Real-world warmth may act through sleep and vigilance
One field study of dormitory residents found that high room temperature and elevated CO2 were among the suboptimal bedroom conditions that negatively affected sleep duration and quality, including lower percentages of REM and slow-wave sleep, and that better sleep quality was associated with better cognitive performance, particularly vigilance and short-term memory [4]. This is an indirect route: warmth in the bedroom may degrade sleep, and degraded sleep may in turn lower next-day cognitive performance. The study did not measure thermal comfort or perceived air quality, so it cannot tell us whether the residents felt comfortable while warm — but it does show a plausible mechanism by which moderately raised temperatures could hurt cognition without anyone noticing at the time.
What this means for judging a room
Taken together, the evidence is consistent with the idea that moderately raised temperatures can impair cognitive performance even when people feel comfortable and rate air quality as fine, but it does not establish that this happens reliably or how large the effect is. The office study that measured comfort, perceived air quality, and cognition together is the most direct test [1], and the wider reviews describe a general thermal-cognition link while flagging inconsistent metrics and limited real-world data [2][5]. A practical implication is that a comfortable rating and a good air-quality rating are not sufficient evidence that cognitive performance is unaffected; if performance matters, it is worth measuring directly rather than relying on how the room feels.
Sources used in this answer
Upper Temperature Limit in Office Environments with Air Movement: Insights from Psychophysiology and Cognitive Performance
An office study exposed 32 participants to varied temperature and air movement and collected subjective thermal comfort, perceived air quality, physiological responses, and cognitive performance, directly addressing whether cognition changes at moderately raised temperatures while comfort and air-quality ratings are also recorded.
Personalized Environmental Control Systems (PECS): Systematic review of benefits for thermal comfort, air quality, health, and human performance
A systematic review of 324 journal articles on personalized environmental control systems found evidence for benefits to human performance, including cognitive function, to be sparse but promising, with inconsistent performance metrics and limited real-world evaluation.
Investigating the Effect of Carbon Dioxide in the Air on the Feeling of Thermal Comfort, Cognitive Function, and Heart Rate of Healthcare Workers while Working
In healthcare workers at a fixed 25°C, exposure to 1800 ppm CO2 versus 1100 ppm was associated with a thermal dissatisfaction score 0.878 units higher and a heart rate 9.25 beats per minute higher, with significant effects involving cognitive performance and CO2 on thermal comfort.
Evaluation of sleep quality and cognitive performance: A case study of Diponegoro University dormitory residents
Among 34 dormitory residents, high room temperature and elevated CO2 negatively affected sleep duration and quality, and better sleep quality was associated with better cognitive performance, particularly vigilance and short-term memory.
INDOOR ENVIRONMENTAL QUALITY AND ACADEMIC PERFORMANCE: A SYSTEMATIC REVIEW OF EVIDENCE FROM TERTIARY INSTITUTIONS
A systematic review of ten studies in tertiary institutions found thermal comfort and indoor air quality had the strongest and most consistent associations with academic performance, with uncomfortable temperatures and high CO2 linked to reduced concentration, cognitive fatigue, and lower test scores, though methodological limitations reduce generalizability.