Energy label for a property: what each class means
The letter on the label isn't calculated from consumption, but from primary energy, and the class boundaries aren't fixed kilowatt-hours. They're multiples of a reference building's value. That's why two equally efficient houses often end up with a different letter. You can work out the annual cost from it, but only via the number printed next to it.
What does the letter actually measure?
A ratio to a reference building, not kilowatt-hours. The regulation doesn't set the class boundaries as a consumption figure. It sets them as a multiple of the value a building of the same size and orientation would reach with reference properties.
| Class | Description | Upper limit for primary energy |
|---|---|---|
| A | Extraordinarily economical | 0.8 times the reference value |
| B | Very economical | 1.2 times |
| C | Economical | 1.6 times |
| D | Less economical | 2.3 times |
| E | Uneconomical | 3 times |
| F | Very uneconomical | 3.7 times |
| G | Extraordinarily uneconomical | above 3.7 times |
The regulation on the energy performance of buildings, as in force on 21 September 2026.
The same scale applies to a new building, to a renovation of a completed building, and to a sale or letting. It's derived from the requirements for a building with near-zero energy consumption.
One practical thing follows from this. A table that assigns each class a fixed range of kilowatt-hours per square metre doesn't come from the regulation currently in force. The reference value is calculated separately for each building, by its type, shape and size. The same letter on a flat and on a detached house therefore doesn't mean the same consumption.
Why do two identical houses get a different class?
Because it's not consumption that's assessed, but primary energy. Every energy carrier has its own factor set in the regulation. The delivered energy is multiplied by it, and only the result decides the letter.
| Heat source | Factor |
|---|---|
| Natural gas, solid fossil fuels | 1.0 |
| Propane-butane, heating oil | 1.2 |
| Electricity | 2.1 |
| Pellets, firewood, wood chips | 0.1 |
| Ambient energy | 0 |
| Electricity exported from the building | -2.1 |
The regulation on the energy performance of buildings, the annex with primary energy factors.
A house with direct electric heating and the same house on gas will therefore get a different letter at identical consumption. Electricity feeds through into the result more than twice as strongly as gas. Pellets and firewood, by contrast, have a factor a tenth the size, so they shift the class even if you don't save a single kilowatt-hour in the house.
A heat pump benefits from two things at once. The electricity that drives it is counted at the full factor, but the heat it draws from the surroundings has a factor of zero. Solar panels that export electricity from the building are subtracted from the result.
Advertising states a single class, and it's precisely this one, for primary energy from non-renewable sources. The letter on a flat listing doesn't tell you what you'll pay for energy. It tells you how much non-renewable energy gets used elsewhere because of it.
How do I work out the annual cost from the class?
Not from the letter. From the number next to it, yes. The certificate's graphic sheet states the indicator values relative to the energy reference floor area, so in kilowatt-hours per square metre per year.
- Take the total delivered energy indicator, not primary energy. Delivered energy is what actually enters the building.
- Multiply it by the energy reference floor area. It's in the report, and it's the external floor area of the heated spaces on every storey.
- Multiply the result by the price per kilowatt-hour from your own tariff. This differs between gas and electricity, so split the consumption by what you heat with.
The result is an estimate, not a bill. The certificate assumes typical use of the building, not yours. Actual consumption varies with how many people live there and what temperature they heat to.
If you want a figure without doing the calculation, ask the seller for the energy billing statements for the last three years. For a flat, the law also treats these as a substitute for the certificate, for a case where the unit owner doesn't receive one. Details are on our page Energy performance certificate.
What will actually improve the class?
The suggestion is already in the certificate. Part of the report is a set of suitable measures to reduce energy performance. It may be left out only where the building has already reached an extraordinarily economical class on both main indicators.
The regulation also states what the set of measures should aim for. For a building below the economical class, the measures should bring it up to the economical class. For a building that's already economical, they should shift it up by at least one class.
Two routes get you there differently. Insulation and new windows reduce both the delivered energy and the average heat transfer coefficient, meaning the actual losses. Changing the heat source changes the factor used to convert delivered energy, so it shifts the letter even without any saving. The effect of both steps is meant to be assessed in the certificate.
Changing the way heating, cooling or hot water is prepared ends the validity of the existing certificate. A heat pump instead of a gas boiler therefore means a new certificate, even if the current one is only a year old.
What does the class do to a mortgage?
Banks give a lower rate for class A or B. What's more interesting is how that discount is built. Komerční banka's internal guidance places a discount for a certificate that's supplied next to a surcharge of the same size for anyone who doesn't supply one.
The deadline is firm. You must supply the certificate no later than before the loan is approved, and under the guidance a condition attached to drawdown can't get around this. Anyone who brings it later can no longer change the rate. The full breakdown, including which property has to meet the condition, is on our page Green mortgage.
The certificate is also one of the documents used for valuing the property, so request it at the start, not at signing. How the valuation works and who pays for it is on our page Property valuation. If you're still building or renovating the property, the state after completion of the work is what gets assessed; see Mortgage for a build and renovation.
Frequently asked questions
Is an energy label the same as a certificate?
In everyday speech, yes, in law, no. An energy label marks products, say a fridge or a washing machine. For a building, the document is called an energy performance certificate, made up of a report and a graphic representation. It's that A4 graphic sheet people informally call the label.
What class does a flat have when the certificate covers the whole building?
Usually the one the building has. The law allows for this: a certificate drawn up for a building also serves as the certificate for a self-contained part of it. A separate certificate for just a flat can be drawn up in two cases. Either the flat has its own heat or cooling source independent of the rest of the building, or it has a separately metered and centrally controlled energy supply.
Will the class improve if I replace the windows?
Losses, delivered energy and the average heat transfer coefficient will fall. Whether that's enough to shift a whole class depends on how far from the boundary the building is. You'll find an estimate right in the certificate, in the set of suitable measures, where the effect of individual steps and how they combine is meant to be assessed.
Why does a house with a heat pump get a better class than one with a gas boiler?
Because of the primary energy factors. Electricity is multiplied by a factor of 2.1 and gas by 1.0, but the heat the pump draws from the surroundings has a factor of zero. Only the electricity driving the pump counts towards the result, and that's a fraction of what the pump delivers to the house.
Where in the certificate do I find the cost in CZK?
Nowhere. The certificate works in kilowatt-hours. Energy prices change and the certificate is valid for ten years, so a figure in CZK would quickly go out of date. You have to do the conversion yourself: multiply the total delivered energy indicator by the energy reference floor area, then by the price per kilowatt-hour.
I'm buying a house in class G. Does it make sense?
It depends on how much the route upwards costs and whether it fits your budget alongside the purchase price. The certificate itself suggests measures and assesses their effect, so you have somewhere to start. But count on two things. A bank won't give an energy-class discount on a house like that. And it's better to finance the renovation together with the purchase, not afterwards.