Heating load

The heating load is the output in kilowatts that your house needs on the coldest day. The heat pump is sized according to this, not according to the old boiler.

The heating load indicates how much heating output (in kW) your house needs to stay warm at the lowest assumed outdoor temperature at the location, the design outdoor temperature. It is not the same as annual consumption: the heating load is an output, whereas consumption is an amount of energy over the entire year.

Why this is important for your house

The heat pump is designed based on the heating load. klimaaktiv points out that, in practice, heating systems are often oversized. This means higher investment costs, poorer efficiency and a shorter lifespan because an oversized appliance frequently switches on and off. Undersizing the appliance, on the other hand, causes the heating element to run too often.

How it is correctly determined

According to klimaaktiv, empirical values or estimates are not enough. The klimaaktiv Wegweiser (guide) requires a heating load design in accordance with ÖNORM EN 12831 or ÖNORM H 7500. Surcharges, for example for domestic hot water and grid operator blocking times, should be taken into account, and oversizing must be avoided. The output of your old oil or gas boiler is not a good benchmark, as older systems were often generously sized.

What you can do

Ask your installer how they calculate the heating load. The correct answer according to klimaaktiv: in accordance with the applicable standard. For an initial guide, you can use the heating load calculator. If the house has been insulated or windows have been replaced since the boiler was installed, the heating load has usually decreased significantly.

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