Display omitted Heating homes using gas boilers is incompatible with the UK’s target of net-zero greenhouse gas emissions by 2050. One solution is to shift to heat pumps (HPs) supplied from decarbonised power plant, but this could place an unmanageable burden on the electricity supply network. National heat demand profiles depend on the heating patterns adopted by households which, in turn, depend on the type of heating system and its control. The largest data sets available, from around 6600 gas-heated homes and 600 homes with HPs, are used to create an empirical model of Great Britain’s (GB) half-hourly domestic heat demand. The model is used to estimate the annual half-hourly heat demand of the GB housing stock for both current and future weather conditions. The demand profile when using HPs is compared to the current profile for gas heating. In a cold year, the calculated total annual heat demand of a typical mix of ground source and air-source HPs was 422TWh, 8% greater for than for gas-heated homes. However, the peak heat demand of 157GW was 8% lower than for gas heating, and the maximum heat ramp rate of 21GW/h, 67% lower. These results are due to the different ways that households use gas boilers and HPs. The accurate modelling of heating patterns is necessary to achieve reliable predictions of national heat demand. Policy initiatives, financial incentives or other interventions that influence the daily pattern of HP usage could also have a marked and positive influence on the GB heat demand profile.