The phrase "to heat the building" means to warm up the inside of a building by increasing the temperature using a heating system or device. Full definition
Consequently, heat moves into an air conditioned building during hot, summer days and out of heated buildings during cold, winter nights. (greenroofs.com)
The demonstration plant uses centralized production of hydrogen to make electricity and heat which is then used to heat buildings in the area. (treehugger.com)
The solar energy heats the building by natural radiation and convection. (eia.gov)