Outside, the sun literally glows on your skin, in the heat it is difficult for you to breathe – but in your own four walls, you can get deep and relaxed air: an air conditioning provides fresh coolness. However, only if their power is sufficient for the room. This UPDATED guide tells you what the power of your air conditioning must be in order for the bedroom, children’s room or conservatory to be pleasantly tempered.
BTU and Watt: These are the Units of Measurement for Air Conditioning
To choose the right air conditioning for your own four walls or for the office, two units of measurement are important in terms of cooling performance: BTU and Watt. BTU stands for “British Thermal Unit” and denotes the energy needed to heat a pound of water by one degree Fahrenheit. In the field of air conditioning, however, BTU stands for BTU/h, i.e. the cooling capacity per hour.
Watt (with the unit sign W) also denotes a certain amount of energy used per unit of time. 1,000 BTU/h corresponds to 293,071 watts. In the following, the required power of the air conditioning system is calculated and specified in watts. If you come across the BTU when searching for the right device, simply take the watt number roughly three times and round it up.
The heat energy, which has to be transported out of space, so to speak, is called a “cooling load”. The cooling capacity, which is indicated by watt in the air conditioner, thus indicates how much cooling load the device can handle.
How to calculate the cooling load depending on the room size
You can obtain a first value for the required cooling capacity per room with the following rule of thumb: Room area in square meters by 60 (with good insulation and little sunlight) up to 100 watts (with little insulation and high solar radiation).
For a 20 square meter room, this means: 20 sqm x 100 W = 2,000 W. Often the cooling load is also expressed in kilowatts (kW) instead of watts. The following applies: 1 kW = 1,000 W. In our calculation example, you need an air conditioner for a cooling load of 2 kW.
Another rule of thumb is cubic meters of space by 40 watts. If the 20 square metre room from the previous example is about 2.5 metres high, you can calculate: 20 sqm x 2.5 m x 40 W = 2,000 W.
Depending on the formula, room height and insulation or window area, you can get the same cooling load: 2,000 watts or 2.0 kW or about 6,800 BTU.
By the way: The required cooling capacity does not have to be provided by air conditioning alone. Instead of a device with 2 kW cooling capacity, you can also choose two devices with 1 kW power each. The advantage: The cool air is distributed more evenly in the room.
These factors affect the cooling load
The calculation of how much power the air conditioner must bring to effectively cool down a room does not only depend on the room size. There are other sources of heat that are considered, for example:
- Which rooms are next to, above or below the room (air-conditioned, basement, attic)?
- How much window area with what sunlight does the room have?
- How is the room insulated? Are there any gaps and gaps, such as doors or exhaust grilles, through which cold can penetrate out and heat?
- How many people are in the room?
- Which technical devices (computers, TVs, but also lighting) eat how much heat?
With air-conditioned adjoining rooms or good insulation, you can set the cooling capacity correspondingly lower, but with many heat sources and weak insulation, you should choose a stronger device.
For each person in the room, you add about 250 watts. For electronic devices, you take the wattage as a scale: If your PC runs with 200 watts of power, add 200 watts to the required cooling power. You can find out how much watts a device takes up on the glued-on nameplate or in the operating instructions.
Online calculator for calculating cooling capacity per room
Whether attic, children’s room or bedroom: each room has its own individual requirements for cooling and thus air conditioning. Online tools will help you with the detailed calculation.
The tool from Thermoflux, a manufacturer of alternative heating systems, is easy to use and shows you the required cooling capacity in watts after a few details.
Here you can find the climate calculator of Klimaworld
Stiebel-Eltron Cooling Load Calculator
The manufacturer Stiebel Eltron also offers a tool. The size and orientation of the walls are displayed as a sketch.
Keep a cool head
Air conditioners ensure a pleasant indoor climate even in the highest heat and stuffy air – provided they provide the necessary performance. In addition to the size of the room, the size of the walls, the orientation and the solar radiation are just as relevant as the number of people in the room or the heat radiation of electrical appliances. How you can keep your room cool to a certain extent even without air conditioning, you can find out here at Robeez.
For a first overview, there are simple formulas of a fist, which are based on the number of square meters and the height of the room. Online tools are available for detailed calculations. The required cooling capacity can also be divided into several devices.
For the exact planning, the choice of the optimal location and, if necessary, the installation of air conditioning systems, you should contact a specialist company.