What is Heating Load? - Summary
The heating load (also called design heat load) describes the thermal power a building requires at the coldest expected outdoor temperature to maintain a defined indoor temperature. It is the central parameter for sizing heating systems.
The Two Components
The heating load consists of two main components:
-
Transmission heat losses (ΦT): Heat that flows through the building envelope (walls, windows, roof, floor) to the outside. This typically accounts for 60-80% of the total heating load.
-
Ventilation heat losses (ΦV): Heat lost through air exchange, including infiltration through gaps and intentional ventilation.
Why is Heating Load Important?
The heating load determines:
- Heat generator sizing: Too large means inefficient operation, too small means insufficient heating
- Radiator sizing: Each room needs radiators that can cover its individual heating load
- Flow temperature: Lower specific heating loads allow for lower flow temperatures, ideal for heat pumps
The Standard: DIN EN 12831
The calculation is standardized in the European norm DIN EN 12831, which defines calculation methods, climate data, and boundary conditions to ensure comparable and reproducible results.