How is a house's energy class calculated? The energy certificate calculation in plain language

Why did our house get an E on its energy certificate (energiatodistus) when the heating bills are low? Detached house owners and housing company (taloyhtiö) boards know the question well. The answer is simple: the energy class assesses the building under standardised use, not your household’s bills. Every house is calculated with the same assumptions – occupied around the clock, at an indoor temperature of 21 °C, with a standard amount of domestic hot water and with the weather of Helsinki-Vantaa, wherever the house is actually located. Your actual consumption is recorded separately on the same certificate, and the official certificate form states that it cannot be compared with the calculated consumption. In this article we explain in plain language how the energy certificate calculation works and what decides the letter – without formulas or class tables.

What does the energy class letter really tell you?

The energy class tells you about the building, not about its occupants. The letter is determined by the E-value (E-luku), and the Ministry of the Environment (ympäristöministeriö) describes the E-value in plain language as follows (our translation): “The E-value is a calculated comparison figure for energy efficiency that allows buildings to be compared on the basis of their standardised use.” The key word is comparison figure. A house’s energy rating exists so that two houses can be compared with each other, whether one is home to a family of five and the other to a single person.

On the A–G scale, A is the most energy-efficient class and G the weakest, and the limits of the letters vary by building type. You will find the limits in the articles building energy classes and energy classes of apartments. Alongside the scale, a designation for zero-emission buildings, A0, has also been laid down: the decree entered into force on 22.5.2026, but putting the designation into practical use awaits the implementing provisions of the EU Energy Performance of Buildings Directive and changes to the energy certificate register.

Why is the energy certificate calculation not based on your heating bills?

In the energy certificate calculation, all houses of the same type are occupied in the same way. Under standardised use

the house is in use around the clock every day, so the ventilation is also calculated to run all the time
the indoor temperature is kept at 21 °C
lighting, household appliances and people produce the same standard amount of heat per square metre, and lighting and appliances consume a standard amount of electricity
the heating need for domestic hot water is 35 kWh per heated square metre per year, but in a small house at most 4,200 kWh per dwelling
the weather is that of Helsinki-Vantaa, whether the house stands in Hanko on the south coast or in Sodankylä in Lapland.

For example, in a 140 m² detached house the standardised electricity for lighting and appliances is about 2,900 kWh per year according to our own example calculation – regardless of how much electricity the family actually uses.

If two people live in the house, the bedrooms are kept cool and little hot water is used, actual consumption easily stays below the calculated figure. The opposite is possible too. That is why the certificate separately records the actual purchased energy for the last full calendar year before the certificate as such, without correcting it for that year’s weather. According to the official certificate form, the E-value is calculated with standardised use so that buildings can be compared with each other, and actual consumption cannot be compared with the calculated consumption. Motiva, the state-owned energy efficiency company, puts it briefly: the certificate reports actual consumption, but the energy class and the E-value are based on calculated consumption.

What decides a house’s energy class?

With use standardised, the letter is decided by the building’s own characteristics:

Heating method and energy carrier: how much energy has to be purchased and in what form – as electricity, district heat, oil or wood.
Insulation: the thermal insulation of the walls, the top floor structure and the base floor.
Windows and external doors: how well they insulate heat.
Ventilation and heat recovery: whether the ventilation is mechanical and whether it recovers heat from the exhaust air.
Airtightness: how much air leaks through the structures. A measured result can replace the default value of the calculation.
Floor area: the E-value is calculated per heated square metre, and the class limits for small houses depend on size. The larger the small house, the lower the E-value the same letter usually requires.

The weight of the energy carrier is explained by the factors. The calculated purchased energy is multiplied by the energy carrier factor before everything is added up and divided by the heated floor area. The factors in force are:

Energy carrier	Factor
Electricity	1.20
Fossil fuels, e.g. oil	1.00
District heating	0.50
Renewable fuels used in the building, e.g. wood	0.50
District cooling	0.28

We explain the background of the factors in the article emission factors of energy carriers. A new decree on the factors is being prepared, but it is not in force, so certificates are calculated with the values above.

The E-value includes the heating of spaces and domestic hot water, ventilation, cooling, and the electricity for lighting and household appliances, but not consumption outside the building, such as car heating outlets, snow-melting systems and outdoor lights. The output of solar panels reduces the E-value only to the extent that it covers standardised consumption, and electricity fed into the grid does not affect it at all.

Law in plain language: the obligation to have an energy certificate comes from the Energy Certificate Act (laki rakennuksen energiatodistuksesta, 50/2013), and the calculation rules are set out in the Ministry of the Environment’s energy certificate decree (ympäristöministeriön asetus rakennuksen energiatodistuksesta, 1048/2017). The decree lays down that the E-value of an existing house is also calculated with standardised use, where the input data are taken from, and which class each E-value leads to. The standardised-use values and the energy carrier factors come from two other decrees, listed in the sources of this article. The current texts are available on Finlex: act 50/2013 and decree 1048/2017.

Where does a house’s energy usually go?

Alongside the calculation, it is worth knowing where the energy goes in real life. According to Motiva, in a small house

space heating typically takes 40–60 per cent of the energy
domestic hot water heating 10–25 per cent
preheating of supply air 5–15 per cent
household and property electricity 20–30 per cent.

For apartment buildings, Motiva gives the breakdown of heat energy: according to its 2017 data, in an old apartment building space heating, including ventilation, takes 70–80 per cent of the heat and domestic hot water heating 20–30 per cent. Electricity is not included in these figures. At national level, according to Statistics Finland (Tilastokeskus), about 65 per cent of the energy used for housing in 2024 went to heating living spaces, 16 per cent to heating domestic hot water, 14 per cent to household appliances and 5 per cent to heating saunas. The figures cover all housing, and the percentages are our own calculation.

These are real-life breakdowns, not results of the energy certificate’s standardised calculation. They show where your own bill typically goes, which is why they can differ from the figures on the certificate.

What E-value gives which letter?

Take, for example, a detached house with 140 m² of heated floor area and an E-value of 200. For a small house of this size, class D covers E-values 169–248, so the house is in class D. When the class is determined, the E-value is always rounded up to a whole number, so 248.3, for example, would already be class E. The limits are our own example calculation from the class limits in the decree.

Even so, the same letter can mean very different amounts of purchased energy. According to our own example calculation, a house of the same size with an E-value of 200 buys about 23,000 kWh of electricity per year when it runs entirely on electricity. In a district-heated house, the same E-value can mean as much as about 49,000 kWh of district heat per year (our own calculation, upper limit), once the house’s standardised electricity for lighting and appliances has first been taken into account. The difference comes from the factors: in the E-value, a kilowatt-hour of district heat weighs less than half as much as a kilowatt-hour of electricity. The figure is an upper limit because the calculation does not take into account the electricity used by fans and pumps.

You will find the limits for houses of other sizes and the full class tables in the articles E-value limits and the E-value table and E-value calculation examples.

Why does an old house come as a surprise?

The letter of an old house often comes as a surprise for two reasons. The first is the energy carrier: the factor for electricity is 1.20, for oil 1.00 and for district heat 0.50. In an electrically heated house, every purchased kilowatt-hour therefore weighs the most in the calculation, even if the electricity bill seems reasonable.

The second reason is missing information. The assessor primarily uses established values, such as drawings, plans, product data and information checked on site. If these are not available, the decree’s default values are used according to the year in which the building permit was applied for. If the application year is not known, it is estimated by subtracting two years from the year of completion. The differences are large: if the permit was applied for before 1976, the U-value of the external wall is assumed to be 0.81, whereas from 2010 onwards the default is 0.17 (the smaller the value, the better the wall insulates). If the permit was applied for before October 2003, the efficiency of heat recovery is assumed to be 0 per cent and the air leakage rate n50 = 6.0 air changes per hour (the higher the figure, the more air the house leaks). Established data take precedence over the defaults, so it pays to dig out the old drawings and the documents of renovations and equipment before the certificate is prepared. Read more in the articles a high-quality energy certificate, how to ensure a good E-value and energy certificate for a post-war veterans’ house.

Also compare only certificates calculated under the same rules: the subscript of the letter, for example 2018 or 2013, tells you which regulations the class was calculated under, and classes calculated under different rules cannot be compared with each other.

How can the energy class be improved?

The E-value goes down when the calculated purchased energy goes down. According to Motiva, the means include heat pumps, a heat-storing fireplace and additional insulation of the structures. Even so, the letter does not always change: in Motiva’s example, three air source heat pumps installed in a 150 m² electrically heated house lowered the E-value from 199 to 166, but the class stayed at D.

Not all savings show up in the E-value. Timing heating for the cheap hours of spot-priced electricity lowers the bill but not the E-value. Draught-proofing, on the other hand, shows up in the E-value only if the improvement is verified with an airtightness measurement. We compiled everyday ways to save in the article energy saving.

We discuss the prices and profitability of renovations in the articles energy renovation, energy renovation of an electrically heated house and housing company energy renovation. A tip for housing companies: the energy grant 2026–2027 of Varke (the Housing Construction Centre of the Finnish State) compares the E-value after the repairs with the E-value at the time the building was constructed.

Check your own house’s energy class

As a rule, the energy class must be stated in public sales and rental listings, so it pays to know the letter before the house or apartment goes on the market. Check your building’s certificate with our energy certificate check tool: certificates for buildings with more than two apartments, such as apartment buildings and terraced houses, can be found in the public register search. Certificates for detached and semi-detached houses are not shown in the public search for data protection reasons, but you can enter the details of your own certificate in the tool’s “Add your own energy certificate” section and compare your house with similar buildings. We tell you more about the register in the article energy certificate register.

If the certificate is missing or has expired, we will prepare a new one – see energy certificate for a detached house or our energy certificate service. Submit a request for a quote and we will tell you the price and schedule.

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