How to make an air conditioner power calculation

How to make an air conditioner power calculation

Air conditioning systems can be found not only in offices and public spaces, but also in many apartments. Now everyone has the opportunity to buy an inexpensive air conditioner. The power of split systems in houses and apartments is enough to cool or heat fairly any rooms.

In this article, we will explain in detail how to determine the power of air conditioners based on the area of the room and show an example of the calculation.

General information

air conditioner in apartmentThe power is selected depending on the area of the rooms in which the devices will be used. It is measured in kW (kilowatt), while the area is measured in sq m or m2 (square meter).

By the volume of the room and some other parameters, you can fairly accurately determine the required power. The standard size of a room in an apartment is 20 m2, sometimes 25 m2. In this article, we will talk about such rooms.

You can also make a simple calculation of the power of air conditioners right now, using the rule-1 kW is equal to 10 sq. m. This rule is used by many buyers. But you should keep in mind that for more accurate calculations, you need to use the formula that we will discuss later.

Calculation formulas

As you now know, power is the main characteristic of any air conditioner. In this article, we will show the calculation of air conditioners by the area of the premises. This technique is suitable for small rooms (up to 50 square meters).

To calculate the power, use the following formula:

Q = Q1 + Q2 + Q3

Q-the power we need to know; Q1 — heat energy from the room; Q2-heat energy from the people in the room; Q3 — heat energy from electrical appliances in the room.


To calculate Q1, use this formula S * h * q/1000 S — room area (in square meters); h-ceiling height (in meters); q-the coefficient to be selected depending on the room’s illumination (30 for dark rooms, 35 for rooms with medium illumination, and 40 for sunny rooms).


An adult emits heat energy:

  • In the absence of physical activity-0.1 kW;

  • When walking — 0.13 kW;

  • Under physical exertion — 0.2 kW.


The computer emits 0.3 kW of thermal energy, and the TV-0.2 kW. Most other electrical appliances emit about 30% of their power.

Calculation example

As an example, we calculate the power of air conditioners for living rooms with an area of 26 square meters. The standard ceiling height is 2.75 meters. The room will only accommodate one person, who uses a computer and a small refrigerator.

And the maximum power consumption of the refrigerator is 165 watts. The window in the room is located on the sunny side.

First, we need to calculate the heat dissipation of the walls and windows (Q1). Let’s use the formula that we wrote earlier. Our calculation will look like this:

Q1 = 26 sq. m.2.75 m40 / 1000 = 2.86 kW

Also remember about the thermal energy (Q2), which is released by the person living in the room. In the room, he will rest, without physical exertion. Therefore, we will choose a coefficient of 0.1 kW.

Do not forget to calculate how much heat energy is released by household appliances located in the the room. The computer allocates 0.3 kW. And the refrigerator emits 0.05 kW., since 0.165kW*30%/100% ≈ 0.05 kW.

We get that Q3 = 0.3 kW + 0.05 kW = 0.35 kW.

Now we have the ability to calculate the power:

Q = Q1 + Q2 + Q3 = 2.86 kW + 0.1 kW + 0.35 kW = 3.31 kW

So, we learned that to cool a room of 26 square meters with windows on the sunny side, in which one person lives, using a computer and a refrigerator, you will need an air conditioner with a power of 3.31 kW.

Most manufacturers have unified power. Suitable for our requirements the device has a power of 3.5 kW.

Pay attention

охлаждение воздухаThere are a number of factors that we did not take into account in the calculations, but they can affect the selection of power. The above calculations are not perfect. They are more accurate than the choice based on the principle of 1 kW = 10 sq. m. But still not accurate enough to be considered a reference.

Let’s go back to the factors that influence the choice of power. It is important to take into account the amount of air that can enter the room through an open window during ventilation. Our calculation method does not take into account open windows. This is due to the fact that when the air conditioner is turned on, it is not recommended to open the windows.

If you decide to add data about open windows to the calculation, simply increase Q1 by 20% to compensate for the heat load. Also add 15% to Q1 if the room is located on the top floor and there is no cold attic on top.

It is also important to take into account the area of the glazing. In typical houses, the windows are small, but in new buildings they often put large double-glazed windows in the floor. The amount of natural light entering the room depends on this. In the calculations, we took into account the windows with an area of up to 2 square meters. For each additional square meter, you need to add 100 watts.


Now you know how to choose air conditioners by the area of the premises. You can independently calculate the power of air conditioners by the area of the premises, but we still recommend that you entrust this task to specialists from the store. They will be able to find out the optimal power of the air conditioner. 

To calculate the power during operation at commercial and industrial facilities, it is necessary to involve third-party specialists. In this article, we have described only one of the calculation methods for household air conditioners.

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