Chennai Study Finds Indoor Temperatures Rarely Drop Below 31 Degrees Celsius

A seven-month study tracking indoor temperatures in 50 low- and middle-income homes in Chennai found temperatures rarely dropped below 31 degrees Celsius and often remained above 34 degrees Celsius for hours after sunset, even in winter. The research, conducted by Climate Trends between October 2025 and April 2026, points to chronic indoor heat exposure driven by climate change, urbanisation and heat-retaining construction materials as a serious and under-recognised public health threat.

Temperatures inside the studied homes frequently exceeded 32 degrees Celsius and climbed above 35 degrees Celsius during warmer months, while relative humidity remained stubbornly above 75 per cent throughout the monitoring period. Night-time heat was identified as particularly alarming, with temperatures peaking around 8 and 9 PM at nearly 34.7 degrees Celsius due to concrete walls and floors releasing stored solar heat. Even in early morning hours, homes saw little relief, with temperatures hovering between 33.8 degrees Celsius and 34 degrees Celsius, meaning residents experienced no meaningful thermal recovery during rest hours.

The study found income determines coping capacity. Every high-income household in the sample had an air conditioner; every low-income household had only a ceiling fan. Critically, the report notes that air conditioning cannot fully mitigate baseline heat exposure embedded in the structure itself, as reinforced concrete buildings retain heat across the 24-hour cycle. Previous research from Ahmedabad and Hyderabad has recorded night-time indoor temperatures running 2 to 5 degrees Celsius hotter than outdoors for the same reason. Research in The Lancet Planetary Health links elevated night-time temperatures to increased mortality during heat wave events.

The report was released at the India Heat Summit 2026, where Union Minister for New and Renewable Energy Pralhad Joshi described heat stress as one of the defining challenges of our times. Climate Trends founder Aarti Khosla said the study highlights how night-time heat retention must receive attention alongside daytime heat policy. Naveen Puttaswamy, co-author and associate professor at SRIHER, said residents face dual threats of heat stress and poor air quality that carry physiological and economic burdens. The findings add to a growing body of evidence calling for building design reforms and materials standards in low-income urban housing.

Key figure — 34.7 degrees Celsius peak night-time temperature