According to the will of the federal government, every newly installed heating system should run on 65 percent renewable energy sources from 2024 onwards.

Now it is becoming more specific which heating systems are then still permitted.

In addition to the electricity-driven heat pumps preferred by Economics Minister Robert Habeck (Greens), so-called hybrid heating systems should also be possible.

This emerges from a concept paper that Habeck's ministry published together with Klara Geywitz's (SPD) building ministry.

Julia Loehr

Business correspondent in Berlin.

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In these cases, the heat pump, possibly also in combination with a solar thermal system, should provide at least 65 percent of the heat for a house.

However, a gas or oil boiler can also be used to “cover peak demand”, says the paper, which is now to be discussed with housing and tenants’ associations.

"A hybrid heating system is ideal if the installation of a heat pump is fundamentally possible, but the building still has a higher heating requirement until energy-related refurbishment is carried out, which is difficult to cover with the heat pump, especially at peak times," write the ministries.

They are reacting to ongoing criticism from the housing industry and construction professionals.

They had warned that pleasant temperatures could hardly be achieved with a heat pump in older existing buildings, and if they did, then only with very high electricity costs for the residents.

For multi-family houses with separate gas floor heating in each apartment, the concept provides for transition periods of up to six years, in which the property must be converted to renewables.

According to the ministry's plans, heating systems based on biomass should also be permitted in addition to hybrid heating systems in order to meet the requirement of 65 percent renewables.

This means that installing a wood pellet heating system would also be an option for many owners.

However, the Federal Environment Agency is likely to criticize this in the discussion process that is now starting.

At the beginning of the year, the authority advised against heating with wood because of the fine dust pollution.