The heating load calculation according to DIN EN 12831 forms the basis for dimensioning all components of a heating system. It determines the design heating load, i.e., the maximum required thermal output at specified outdoor temperatures and desired indoor temperatures. The calculation accounts for transmission heat losses through walls, windows, roofs, and floors, as well as ventilation heat losses from infiltration and controlled ventilation. Additional warm-up allowances for intermittent operation are also included. An accurate heating load calculation prevents oversizing or undersizing of boilers, radiators, and pumps. It also forms the basis for hydraulic balancing and serves as documentation for the building energy certificate.