Guide

Heating and energy: what the 2026 Building Modernisation Act changes for flat buyers

The former Building Energy Act (Gebäudeenergiegesetz, GEG), often called the “Heating Act” (Heizungsgesetz), was fundamentally revised in 2026 and is now called the Building Modernisation Act (Gebäudemodernisierungsgesetz, GModG). For buyers of older flats, the rules on existing heating systems and on the energy performance certificate are particularly important.

Legislation and entry into force

The Bundestag passed the GModG on 10 July 2026; the Bundesrat did not call on the Mediation Committee. The act was promulgated in the Federal Law Gazette on 28 July 2026 (BGBl. 2026 I Nr. 226), and its core rules came into force on 29 July 2026. Further parts follow in stages in 2027, 2028 and 2030.

In substance it is not an abolition but a reform: the GEG continues under a new name and with amended obligations. Further legal challenges to the act are expected; details may still change through subsequent legislation.

What applies to heating systems

The obligation to use at least 65 % renewable energy when installing a new heating system (§ 71 GEG, old version) has been abolished. Oil and gas heating systems may continue to be operated and may also be newly installed.

For newly installed gas, oil or liquefied gas heating systems, a so-called bio-fuel staircase (Bio-Treppe) applies instead: a minimum share of climate-friendly fuels (biomethane, bio-oil, hydrogen) of 10 % from 2029, 15 % from 2030, 30 % from 2035 and 60 % from 2040. It can also be met via hybrid systems with a heat pump or solar thermal. From 2045, heating fuels must be completely climate-neutral.

The previous obligation to replace boilers more than 30 years old (§ 72 GEG, old version) has been abolished without replacement. For operators of existing gas and oil heating systems, a quota for green gas or green heating oil is planned from 2028, the details of which are to be regulated by a further act by the end of 2026.

Costs for landlords

For newly installed gas or oil heating systems, network charges, CO₂ costs and additional costs for bio-fuels are in principle to be split equally between landlord and tenant under the amended rules of the Carbon Dioxide Cost Allocation Act (CO₂-Kostenaufteilungsgesetz). For existing heating systems, CO₂ costs continue to be allocated according to the tiered model based on the building's energy consumption.

According to specialist reports, anyone installing a heat pump that does not meet the statutory efficiency requirements risks only being able to pass on modernisation costs to tenants to a limited extent. Have modernisations assessed legally and technically in advance.

Energy performance certificate on sale

Sellers or estate agents must present an energy performance certificate or a copy to prospective buyers at the latest at the viewing; this can also be done by displaying it clearly. If no viewing takes place, it must be presented without delay, at the latest on request. After conclusion of the purchase contract, it must be handed over to the buyer without delay (§ 80 (4) GModG).

In commercial property advertisements – where an energy performance certificate exists – the type of certificate, the energy demand or consumption value, the main energy source, the year of construction and the efficiency class must be stated (§ 87 GModG). An energy performance certificate is valid for ten years.

What this means for older flats

For buyers of existing flats, the GModG removes the immediate pressure to replace a functioning oil or gas heating system. In the long term, however, the costs of fossil fuels will rise due to the CO₂ price, the bio-fuel staircase and the green gas quota.

Check before buying: age and type of the central heating, resolutions of the owners' association on heating, insulation or windows, the amount of the maintenance reserve and the efficiency class in the energy performance certificate. With individual heating in the flat (e.g. gas floor heating – Gasetagenheizung), decisions often affect only the individual owner.

Reading the energy performance certificate

There are two types: the demand-based certificate (Bedarfsausweis) calculates energy demand from the construction and building services, while the consumption-based certificate (Verbrauchsausweis) is based on the occupants' actual consumption in recent years. Consumption values depend heavily on user behaviour and vacancy; demand values are more comparable between buildings.

Residential buildings are classified into efficiency classes from A+ (very efficient) to H. For older buildings, pay attention to the figure in kWh per m² per year, the energy source and the modernisation recommendations attached to the certificate.

According to the BBSR information portal, transposition of the EU Energy Performance of Buildings Directive (EPBD) is to follow later in a separate step; the contents of the energy performance certificate may therefore still change.

Sources

• https://www.haufe.de/immobilien/wirtschaft-politik/gebaeudemodernisierungsgesetz-gmg_84342_683694.html
• https://www.ebnerstolz.de/de/unser-angebot/leistungen/rechtsberatung/energierecht/gebaeudemodernisierungsgesetz-verabschiedet-109427.html
• https://www.gmodg.bund.de/GModG/DE/Home/startseite/GModG_News/GModG_News-node.html
• https://www.buzer.de/80_GModG.htm
• https://www.buzer.de/87_GModG.htm
• https://www.hausundgrund.de/sites/default/files/secure_downloads/W16%20-%20GModG%20%E2%80%93%20Geb%C3%A4udemodernisierungsgesetz%20-%20Pflichtangaben%20in%20Immobilienanzeigen.pdf
• https://www.gesetze-im-internet.de/co2kostaufg/

General information, as at October 2026. It does not replace advice from a tax adviser, solicitor or notary.