Objective: This study examines the extent that temperatures in English living rooms correspond to standard assumptions made in established UK building stock models. Methods: Spot temperature measurements taken every 45 minutes over 92 winter days in 248 homes in England were analysed and compared to the assumed thermostat setting of 21°C inside and outside the assumed heating periods. Results: Homes on average displayed lower internal temperatures during assumed heating periods and significantly shorter durations of heating to 21°C than common models assume, with about 20% of homes never reaching the assumed demand temperature of 21°C. Data showed a difference of only about 45 minutes in the duration of temperatures at or above the demand temperature for weekdays and weekends, contrary to the assumed difference of seven hours. Variability between homes was large. Conclusion These findings suggest that currently used standard assumptions of heating demand and heating duration do not accurately reflect the living room temperatures of dwellings in England. Practice implications: Standard assumptions might have to be revised, in particular regarding the weekday - weekend differentiation. The prediction of internal temperature for a given home contains potential large error when using standard assumptions.