Air Conditioner Operating Costs

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When people buy an air conditioner, they mostly focus on the price of the unit and installation. The question "how much will it cost to run" often only comes up during the first hot summer or the first heating season, once they notice a higher electricity bill. Yet an air conditioner's running costs can be estimated fairly accurately even before purchase, if you know a few basic figures: the unit's power draw, energy class, the size of the space, and how many hours a day you'll actually use it. In this article we break down running costs in practical terms, using specific examples, including a comparison of cooling and heating and what most affects the final amount on your bill.

What makes up an air conditioner's running costs

An air conditioner doesn't consume electricity according to its cooling or heating output, but according to its power draw - i.e. how much electrical energy it needs to deliver that output. The ratio between output and power draw is called EER (cooling) or COP/SCOP (heating), and it's precisely this number that determines whether running the unit will be cheap or expensive. A modern inverter air conditioner with an A++ or A+++ energy class can produce 3 to 5 kW of cooling or heat from 1 kW of electricity. An older, non-inverter unit, or one in a lower class, produces only 2 to 2.5 kW from the same amount of electricity.

Specific costs are therefore made up of five variables that build on each other:

Electricity price - in this article we work with a typical household rate of around €0.19/kWh, which corresponds to the average price most households in Slovakia faced in 2026. If your rate is cheaper or more expensive (e.g. a dual-tariff rate with night electricity), you can easily recalculate all the figures below by proportion.
Rated output of the unit - the larger the space you're cooling or heating, the more powerful a unit you need, and the higher its power draw.
Energy class (EER/SCOP) - the difference between class A++ and an older class A unit can mean a 30-40 % difference in consumption at the same output.
Temperature difference - the bigger the difference between the outdoor temperature and the desired indoor temperature, the harder the compressor has to work, and the higher the consumption. Cooling from 35 °C to 24 °C is substantially more demanding than from 28 °C to 24 °C.
Operating time - how many hours a day and how many days in the season you actually use the unit.

The diagram below shows how these variables build on each other and gradually combine into the final monthly or seasonal figure on your bill.

Model calculation: how much does cooling a flat cost over summer

Let's walk through a specific calculation using real units. Take three Vaillant Climavair Pro wall-mounted air conditioners with output classes of 2.7 kW, 3.5 kW, and 5.0 kW - a typical range for a smaller room, a larger room/smaller flat, and a living room or larger open space. We use an A++ energy class and an average seasonal EER of around 3.2 (a common value for a quality inverter split unit in real operation, not just a peak laboratory value).

An important note on methodology: an inverter air conditioner does not run continuously at 100 % output. After cooling the room to the required temperature, the compressor slows down or briefly switches off, only maintaining the temperature. In real operation, therefore, an average load of around 50 % of rated output is used, not constant full power. For usage of 6 hours a day during the hottest 90 days of the year (June to August), the following approximate seasonal costs come out:

2.7 kW unit - average power draw at 50 % load approx. 0.42 kW, consumption approx. 2.5 kWh/day, cost approx. €0.48/day, per season (90 days) approximately €43.
3.5 kW unit - average power draw approx. 0.55 kW, consumption approx. 3.3 kWh/day, cost approx. €0.62/day, per season approximately €56.
5.0 kW unit - average power draw approx. 0.78 kW, consumption approx. 4.7 kWh/day, cost approx. €0.89/day, per season approximately €80.

These are model figures for moderately intensive use (6 h/day). If someone leaves the air conditioner running practically all day including at night (for example due to health issues or working from home in an attic), real consumption can climb to double. Conversely, if used only during the hottest afternoons (2-3 hours a day), costs will be significantly lower, often under €20-25 for the whole summer.

The chart below compares these three model seasonal costs side by side, so you can see at a glance how costs rise with the size/output of the unit - which is also the reason it pays to choose output based on the room's actual need, not "bigger just to be safe".

How costs differ by energy class

Just as important as output is the age and energy class of the unit. If we compare the same 2.7 kW unit at three different efficiencies - a modern A++ (EER approx. 3.2), an older A+ (EER approx. 2.6), and an older non-inverter class A unit or worse (EER approx. 2.0) - at the same usage (6 h/day, 90 days), the following seasonal costs come out:

A++ (modern inverter): approx. €43 per season
A+ (older, still decent): approx. €53 per season
A or older, non-inverter: approx. €69 per season

The difference between the best and worst unit in this model example is approximately 60 % extra cost purely due to lower efficiency. With longer usage (e.g. 10 h/day in an office or business), this difference grows even further in absolute terms. This is exactly why, when replacing an old air conditioner, it's worth factoring in not just the price of the new unit, but also how many years it takes for the difference in consumption to pay itself back through lower bills.

Heating with an air conditioner - a cheaper alternative to direct electric heating

Most modern wall-mounted split air conditioners, including the Vaillant Climavair Pro units, also handle heating in air-to-air heat pump mode. This means the same principle that removes heat from a room in summer removes heat from the outdoor air in winter and delivers it indoors. The advantage over direct electric heating (e.g. a classic electric convector or direct-heating panels) is fundamental - a heat pump can produce 3-4 kW of heat from 1 kW of electricity, while direct electric heating produces at most 1 kW of heat from 1 kW of electricity (efficiency close to 100 %, but no multiplying effect).

In a model calculation for a 2.7 kW unit, a 150-day heating season (October to March), and average usage of 8 hours a day, with an average SCOP of around 3.8 (a common value for a quality A+++ unit across a mix of milder and colder days), we get:

Heating with an air conditioner (heat pump): average power draw approx. 0.43 kW at 60 % average load, consumption approx. 3.4 kWh/day, cost approx. €0.65/day, over the whole season (150 days) approximately €98.
The same heat output via direct electric heating (COP=1): consumption approx. 12.96 kWh/day, cost approx. €2.46/day, per season approximately €369.

The difference is therefore roughly threefold in favour of the air conditioner/heat pump. This is also why more and more households, when renovating heating in smaller flats or as a supplementary heat source during the transitional months (autumn, early spring), reach for a wall-mounted air conditioner with a heating function instead of classic electric radiators. However, keep in mind that at very low outdoor temperatures (below -5 to -10 °C, depending on the specific model) the heat pump's efficiency drops, and the unit is generally not intended as the sole and main heat source for a whole house, but rather as a supplementary or main source for a single room or smaller flat.

If we add up the year-round costs for a single 2.7 kW unit - cooling in summer (€43) plus heating in winter (€98) - we get approximately around €141 a year in electricity for both functions combined. For a unit that would otherwise only handle cooling, with heating provided by another source (e.g. a gas boiler or electric convectors), you should also make this comparison against the cost of that alternative heat source.

Recommended models by output and planned space

When choosing a unit, it's worth basing your decision on the actual size and orientation of the room (a south-facing room with sun all day needs more output than a north-facing room), not just a flat rule of "1 kW per 10 m²". Below are three specific models from the same series that cover the typical range from a smaller room to a larger open space.

VAIB1-025WN outdoor and indoor unit with remote control - with an output of 2.7 kW, this is a typical choice for a smaller bedroom, children's room, or home office up to approx. 20-25 m². We used exactly this model for the model costs above (€43 for the summer season, €98 for the heating season). Price from €527.

VAIB1-035WN outdoor and indoor unit with remote control - the 3.5 kW output class is suitable for an ordinary living room or larger room up to approx. 30-35 m², or a room with more glazing. In the model calculation above, its summer operation works out to approx. €56 per season. Price from €561.

VAIB1-050WN outdoor and indoor unit with remote control - with an output of 5.0 kW it covers an open living space connected to a kitchen, an attic with sloped ceilings, or a room with a higher heat load. Higher output also means higher running costs (approx. €80 for the summer season in the model example), so it's worth reaching for this model only if the actual size of the space calls for it - an oversized unit tends to cycle on and off more frequently, which can ultimately be less efficient than a correctly sized smaller unit. Price from €833.

Clear comparison of the three models

The following graphic summarises all three models side by side - output, approximate unit price, and model seasonal cooling costs, as calculated above.

Practical examples from an ordinary household

A few real-life situations that recur among customers and illustrate well why running costs vary so much from house to house:

A flat on the top floor, room facing southwest. Such a room heats up significantly during summer from midday onward, and the air conditioner in it runs practically all afternoon and evening. Even with a correctly sized unit, you need to expect a longer operating time here (easily 8-10 hours on the hottest days) than in the model case above, and therefore higher costs - approximately 30-50 % more than our 6-hours-a-day model.

An office with several computers and printers. Electronics in the room produce extra heat that the air conditioner also has to "work off", even though it doesn't show up on a thermometer measuring the outdoor temperature. When choosing output for a workspace, it's therefore worth including an extra reserve compared to a purely residential room of the same size.

A household using the air conditioner also for spring/autumn top-up heating. If someone uses an air conditioner with a heat pump function only as a supplement to the main heating during the transitional months (e.g. to warm the room in the morning before the main boiler kicks in), the real costs will be considerably lower than the full-season model above, because the operating time is shorter and outdoor temperatures are milder, where the unit's SCOP is even higher.

A set temperature 1-2 °C lower/higher than necessary. A common mistake that can raise costs by tens of percent - every extra degree of difference between the outdoor and the set indoor temperature increases the compressor's load. The recommended temperature for cooling is 24-26 °C (not 18-20 °C), and 20-21 °C for heating. The difference in comfort is minimal, the difference in consumption is noticeable.

How to actually reduce running costs

Besides correctly choosing output and energy class, we can also influence costs through everyday use:

Don't push the temperature too low. Every extra degree towards an extreme costs further percentage points of consumption. A difference of up to 8-10 °C between outdoor and indoor temperature is comfortable for the body and efficient for the unit.
Close blinds/shutters during the strongest sun. Direct sunlight through a window can bring a heat load into a room comparable to a small heater - shading significantly eases the air conditioner's work.
Keep doors and windows closed during operation. This seems obvious, but frequent ventilation "for a bit of fresh air" while the air conditioner is running is one of the most common causes of higher-than-expected consumption.
Clean the filters regularly. A clogged filter increases airflow resistance, and the unit has to work harder for the same result. The recommended interval is once every 2-4 weeks during the season.
Use a timer/scheduler. Setting the unit to pre-cool the room shortly before you get home, instead of running "for nothing" all day, can save a significant share of daily consumption.
Service before the season. A refrigerant shortage or a dirty heat exchanger can worsen a unit's EER just as much as if you'd bought a model a whole class worse - regular servicing therefore directly translates into your electricity bill.

Is it worth replacing an old air conditioner with a new one for the cost savings?

This question comes up most often when a household has an older, non-inverter air conditioner (typically 10-15 years old) and is deciding whether to let it run out its life or replace it with a new inverter model. The answer depends mainly on two things - how many hours a year the unit actually runs, and how big the difference in energy class is between the old and new model.

Let's go back to the figures from the energy class comparison above. At 6 hours a day over a 90-day summer season, the difference between class A++ (€43) and an older non-inverter unit (€69) came out to approximately €26 for one summer season. If the unit also serves as a heating source (where the difference in efficiency between an old COP and a modern SCOP is usually even more pronounced, since older units tended to have a weaker or non-existent heating function at lower temperatures), the year-round saving can range from €60-100 a year for typical family use.

At a purchase price for a modern unit of around €500-850 (see the models below), this means the investment in a new unit pays for itself in roughly 6-10 years purely from the electricity savings - and that's without counting other advantages of a new model, such as quieter operation, better air filtration, more precise temperature control, or a longer warranty. With more intensive use (for example in a business where the unit runs 10-12 hours a day for most of the year), the payback period shortens in proportion to the higher number of operating hours, potentially to as little as half the period stated above.

If the old unit has also gone years without proper servicing (no refrigerant top-ups, a dirty heat exchanger), its real efficiency may be even lower than the model value stated above for an "old but functional" class A unit - in that case, replacement generally pays off even sooner than the approximate figures above suggest.

How to calculate your own cost estimate

If you want to make your own estimate for your specific situation, the procedure is simple and follows the same principle used in all the examples above:

Find out the unit's rated cooling or heating output in kW (stated in the technical data sheet or in the model name).
Multiply it by the estimated average load in real operation - for typical use in a well-insulated room, count on 40-60 %; for a higher heat load (south-facing, large glazing, electronics), count on 70-90 %.
Divide the result by the unit's energy coefficient (EER for cooling, SCOP for heating) - if you don't know it, use an approximate value of 3.0-3.5 for class A++, and 3.5-4.5 for A+++.
You get the estimated average power draw in kW. Multiply it by the number of hours of operation per day - you get daily consumption in kWh.
Multiply daily consumption by the electricity price on your tariff (if you don't know the exact value, use €0.19/kWh as a typical average) - you get the daily cost.
Multiply the daily cost by the number of days you plan to use the unit in that season - you get the seasonal cost.

This procedure won't give a perfectly exact figure (real operation varies from day to day depending on the weather), but it provides a reliable enough estimate to compare models against each other or to plan a family budget for the coming summer or winter.

Frequently asked questions

How much does it really cost to run an air conditioner all day in summer?

For a medium-sized unit (2.7-3.5 kW) in class A++ running 10-12 hours a day during the hottest days, the daily cost works out to approximately €0.8-1.3. For a full month of intense summer (July) this can be roughly €25-40, depending on actual temperatures and the room's set temperature.

Is heating with an air conditioner cheaper than electric convectors?

Yes, usually significantly so. An air conditioner in heat pump mode can produce 3-4 kW of heat from 1 kW of electricity, while direct electric heating produces at most 1 kW of heat from 1 kW of electricity. In the model example above, the difference worked out to roughly threefold in favour of the air conditioner.

Is it worth buying a more powerful unit "just to be safe"?

In most cases, no. An oversized unit not only costs more to buy, but in operation cycles on and off more frequently, which can reduce its effective service life and, ultimately, need not be cheaper or more economical than a correctly sized model. It's worth getting advice on output based on the room's actual size, orientation, and glazing.

How much does energy class really affect actual consumption?

A lot. In our model calculation, the difference between class A++ and an older non-inverter class A unit came out to approximately 60 % higher consumption with exactly the same output and the same usage. Over long-term use (years), this saving can pay back several times over compared to the difference in purchase price.

Can an air conditioner's consumption be measured separately?

Yes, most simply with a separate consumption meter (a wattmeter) connected between the socket and the outdoor unit's power cable, or, if the model supports it, via the unit's app, which on some more modern units shows an estimated consumption directly in the controls.

Does it make sense to switch the air conditioner off and on again, or is it better to leave it running continuously at lower output?

For longer periods of use (a whole afternoon or more), it's generally more efficient for an inverter unit to run continuously at a moderate output than to repeatedly switch off and restart at full power - restarting and re-cooling the room from a higher temperature consumes more energy than maintaining a temperature already reached.

Do you have a question about this topic?

Can't decide, or dealing with a specific situation in your household? Write to us - we're happy to help.