Heating: calculation values ​​and standard specifications

The calculation of the heating system is standardized in DIN EN 12831. There, the permissible calculation methods are also regulated. However, they are extremely complex and therefore can only be used correctly by professionals. The most important terms from the heating calculation can be found here.

heating loads

A heating load is always the amount of heat that must be supplied to a room or building in order to maintain a specific room temperature. For the calculation, which is prescribed in all details, building physics methods are used.

The following factors are taken into account when calculating heating loads:

  • the location of the building
  • Size and type of heat-transferring surfaces on the building
  • the purpose of individual rooms and areas

Different types of heating load are distinguished.


The standard heating load is calculated according to the procedure prescribed in DIN EN, whereby the so-called transmission heat loss (heat loss through components, windows and doors) and the so-called ventilation heat loss are included. The U-values ​​of the components also play a role here.

On the other hand, what is not taken into account - and this justifies criticism - are the so-called solar gains (that is, the effect of heating up by solar radiation, which can be considerable). Also, the so-called internal gains (heating by devices in the room, such as waste heat from the refrigerator or by the body heat of people in the rooms) are not taken into account.

For passive houses, these factors play an important role. They are always included in the overall conception of the building.


The design heating load determines the dimensioning of the heating system and also the dimensioning of the areas of the space heating. In the case of heat pumps, the shutdown times of the electricity suppliers must also be taken into account case by case.

additional heating load

It usually does not matter, except when heating is interrupted. However, in buildings heated by heat pump technology, it may sometimes be necessary to consider them.

If up and down times are to be taken into account, these must first be determined in writing. Calculation can only be made on the basis of specific lowering and lowering temperatures.

Standard outdoor temperature

Also for the outdoor temperature averages, which are needed for all calculations, there are binding specifications. You can find it on the so-called isotherm map, plus there are also climate tables and average temperatures for all of Germany.

Pipe network calculation and hydraulic adjustment

These calculation methods, which are also standardized, are applied to hot water central heating systems.

Video Board: Pump CALCULATIONS, Flow rate, RPM, Pressure, Power, Diameter