Technical condition and energy

Energy class G (energetická třída G)

In Czech: Energetická třída G

Energy class G (energetická třída G) is the lowest rating on the Czech energy certificate scale, meaning an exceptionally inefficient building. In an advert it can also appear simply because the agent never received a certificate.

Also called: class G, G rating, energetická třída G, třída G, mimořádně nehospodárná

What it means

In the energy performance certificate (PENB), G is the last of seven classes. Decree No. 264/2020 Sb. calls it exceptionally inefficient (mimořádně nehospodárná). A building rated G needs, according to the calculation, much more energy than buildings in better classes; typical reasons are poorly insulated walls and roof, old windows or an outdated heat source.

In Czech listings, though, energetická třída G has a second possible meaning. The energy management act requires an estate agent who has not received the graphic part of the certificate from the owner to state the worst class in the advert, and under the decree that is G. So a G can describe the real building, or only the fact that no certificate was handed over.

How it works in the Czech Republic

When a certificate exists and shows G, the rating is the outcome of an assessment made with a uniform method. Read the whole document, ideally with someone who understands it, and find out what pulls the result down: the walls and roof, the windows or the heating.

When the agent has no certificate, the G tells you nothing about the building. It might be a well-renovated house or one that would genuinely score badly. Either way, the owner must show the certificate to an interested buyer or tenant before the contract is concluded and hand it over at the latest when the purchase agreement (kupní smlouva) or lease is signed, so you can ask for it.

The practical test is simple: ask for the certificate. If you get one rated G, factor it into your estimate of running costs and possible upgrades. If there is none, or the seller will not show it, ask why. These rules reflect the situation as of October 2026.

Practical example

For example, you see two similar flats on the same street, both marked G. For the first, the agent sends a certificate showing uninsulated walls and original windows. For the second, the agent explains that the owner has not supplied a certificate yet. The first flat really is inefficient; about the second you know nothing yet, and its G says nothing about its condition.

What to watch out for

  • Ask directly: is the G taken from a certificate, or is the certificate missing?
  • If a certificate exists, request the full document including its issue date.
  • With a genuine G, budget for higher energy costs or for upgrades to the building.
  • A missing certificate does not mean the building is bad, or good; check its condition at a viewing.
  • When negotiating the price, rely on the documented condition rather than the letter in the advert.

Frequently asked questions

Does class G in an advert always mean a bad building?

No. It may be the real result of a certificate, or the agent may not have received one and is required by law to show the worst class. Only the certificate itself settles it.

What is the official name of class G?

Decree No. 264/2020 Sb. names it mimořádně nehospodárná, which means exceptionally inefficient. It is the worst of the seven classes from A to G.

Can I ask for the certificate if the advert says G?

Yes. The owner has to show it to you before the contract is concluded and hand it over no later than at signing.

  • Energy performance certificate (PENB)PENB (průkaz energetické náročnosti budovy) is the Czech energy performance certificate. It rates how much energy a building or flat needs and places it in a class from A (exceptionally efficient) to G (exceptionally inefficient).
  • Thermal insulation (tepelná izolace)Thermal insulation (tepelná izolace) is a material or layer that limits heat loss through a building's walls, roof and floors. An insulated house needs less energy for heating, which can show as a better class in its PENB.
  • Renovation (rekonstrukce)Renovation (rekonstrukce) means repairing or modernising a flat or house by renewing parts of it, such as wiring, plumbing, the bathroom, windows or roof. In Czech listings the word can cover anything from new floors to a full rebuild.
  • Heat pump (tepelné čerpadlo)A heat pump (tepelné čerpadlo) heats a home, and often its water, by taking heat from the outside air, the ground or water and moving it indoors using electricity. How well it works depends on its design and on the house's insulation.
  • Lease agreement (nájemní smlouva)A lease agreement (nájemní smlouva) is the contract under which a landlord lets a flat or house to a tenant for temporary use in exchange for rent. Residential leases in Czechia are governed by the Civil Code.

Sources

Laws and official pages this text is based on (in Czech).

This text is for information only and has not yet been checked by a legal or financial expert. It is not legal, tax or financial advice. Verify important details in the listed sources or with a professional.

Updated 25 October 2026

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