New Heating System: How Much Can Your Rent Rise in 2026?

What this is about

Your landlord plans to replace the old heating with a heat pump or a new gas boiler. How much can the rent go up afterwards? Since 29 July 2026 the rules of the Act of 23 July 2026 (BGBl. 2026 I Nr. 226) apply. The former Building Energy Act (GEG) is now the Gebäudemodernisierungsgesetz (GModG); the heating rules are in §§ 42 to 46 GModG.

A heating replacement counts as modernisation

Under § 555b Nr. 1a BGB, installing a heating system within the meaning of § 42 GModG is a modernisation measure. As a rule, you have to tolerate it (§ 555d Abs. 1 BGB), but the costs cannot be passed on without limits.

How much the rent may rise

With subsidies (§ 559e BGB): If the landlord received public grants, the annual rent may rise by 10 % of the costs for your flat, minus the subsidies. A flat 15 % of the costs counts as maintenance and is excluded. This deduction does not apply to the costs of a gas, oil or LPG heater under § 43 GModG.

Subsidy available but not used: The increase then follows § 559 BGB (8 % of the costs).

Cap: For the heating installation, the monthly rent may rise by no more than 0.50 EUR per square metre within six years (§ 559e Abs. 3, § 559 Abs. 3a sentence 3 BGB). The general caps still apply: a total of 3 EUR per square metre within six years, or 2 EUR if the rent was below 7 EUR per square metre.

Example: Your 70 m² flat is allocated 14,000 EUR of the cost of a heat pump, with a subsidy of 4,000 EUR. After the flat deduction, 11,900 EUR remain (14,000 × 0.85); minus the subsidy, 7,900 EUR. 10 % of that is 790 EUR a year, or about 65.83 EUR a month. The cap, however, only allows 70 × 0.50 = 35 EUR a month. That is the maximum for this measure within six years.

New: heat pumps and the seasonal performance factor (§ 559f BGB)

For a heat pump, the landlord can claim the full increase only if a qualified contractor proves a seasonal performance factor (Jahresarbeitszahl) of at least 2.5. No proof is needed if, for example, the building was constructed after 1996 or can be heated with a flow temperature of no more than 55 °C; the law lists further exemptions.

If the proof is missing and no exemption applies, the landlord may base the increase on only half of the costs. In the example, that would be 7,000 EUR instead of 14,000 EUR.

Announcement and hardship objection

The landlord must announce the work in text form at least three months before it starts (§ 555c BGB). It must state the type, scope, start and duration of the work, the expected future operating costs and, for an increase under § 559 BGB, the expected rent increase. It should explain how and by when to raise hardship.

You can raise hardship grounds in text form until the end of the month following receipt of the announcement (§ 555d Abs. 3 BGB). The deadline only starts if the announcement meets the legal requirements. An increase may be excluded where, including future operating costs, it would cause unjustifiable hardship (§ 559 Abs. 4 BGB). For a heating installation under § 555b Nr. 1a, this also applies if the landlord was legally required to replace the system.

The increase must be declared in text form, calculated and explained (§ 559b BGB). Without a proper announcement, payment starts six months later.

An index-linked rent (Indexmiete) does not rule out such an increase (§ 557b Abs. 2 BGB).

New gas or oil heater: shared CO2 costs

If the landlord installs a gas, oil or LPG heater under § 43 GModG, landlord and tenant each bear half of certain costs under § 5a CO2KostAufG:

• from 1 January 2028, the gas network charges and the CO2 costs,
• from 1 January 2029, the cost of the mandatory share of bio or green fuels, up to a share of 30 %.

Example: If the 2028 heating cost statement shows 200 EUR of CO2 costs for your flat, your share is 100 EUR.

§ 5d CO2KostAufG allows an exception in narrow hardship cases, among other conditions only outside tight housing markets and with a rent below 85 % of the local comparative rent. The landlord must tell you in text form.

What you can do

• Check the announcement: Is it in text form, on time and complete? If something is missing, the hardship deadline may not start.
• Raise hardship in time: Low income, age or illness can be reported in text form.
• Recalculate the increase: Check the costs, subsidies, the 15 % flat deduction and the 0.50 EUR per square metre cap.
• Ask about heat pumps: You can request the proof of the seasonal performance factor or the exemption relied on. If neither is given, the increase may be too high.
• Check heating statements from 2028: Has the half-and-half split of CO2 costs and network charges been applied?

This article is general information, not legal advice. For your specific case, a tenants' association (Mieterverein) or a tenancy lawyer can help.