Air conditioning BTU calculator

Q: What is BTU/h in air conditioning?

BTU/h (British Thermal Unit per hour) is a unit that measures the cooling or heating power a system can provide or extract from the environment per hour. It is commonly used to express the capacity of air conditioning and heating equipment.

Q: Are BTU/h and kW the same?

No. BTU/h measures thermal energy transfer rate (cooling/heating capacity), while kW (kilowatt) is the official SI unit for electrical power (how much electricity is consumed) or thermal power. They are related by a conversion factor (1 kW ≈ 3412 BTU/h), but they represent different aspects of energy.

Q: How do I calculate the required BTU/h according to surface?

A common rule of thumb is about 400 BTU/h per m²; for very sunny rooms, it might increase to around 520 BTU/h per m², but other factors must also be considered for an accurate calculation.

Q: How to calculate BTU/h from cubic meters?

Multiply the volume (m³) by 160; for example, 50 m³ × 160 = 8000 BTU/h.

Q: What additional factors should I consider in the calculation of BTU/h?

You must include: number of people (approx. 450 – 900 BTU/h per person depending on activity), watts of electrical equipment (~ 2.5 - 3.8 BTU/h per W), solar orientation, number of windows, type of wall insulation, etc.

Q: How do I convert electrical watts to BTU/h?

Each watt is approximately equivalent to 3.41 BTU/h (1,000 W ≈ 3412 BTU/h).

Q: Is official registration required for equipment with a certain amount of BTU/h?

In Spain, equipment with more than 18,000 BTU/h (≈ 5 kW thermal) must be registered according to regulations.

Q: Why is it important to properly size an air conditioner?

An oversized unit cools quickly but may not dehumidify well, leading to a clammy feeling. An undersized one consumes more energy trying to reach the desired temperature and does not cool effectively, leading to discomfort and higher bills.

Q: What information do I need to calculate the electrical consumption of my appliances?

You need to know the power of the appliance, which is usually indicated on a plate on the back or bottom of the device, expressed in watts (W). You should also estimate the number of hours it is used each day.

Q: Where can I find the power of an appliance?

The power of an appliance is usually indicated on a plate located on the back, bottom, or side of the device. This plate shows technical data such as voltage (V), current (A), and power (W).

Check instantly the BTU/h needed for your room! Check out our air conditioning BTU calculator, very easy to use:

Air conditioning BTU calculator

Area (m²):

Ceiling Height (m):

Number of Occupants:

Type of Activity:

Building Insulation Type:

Area of windows exposed to sun (m²):

Window Type:

Total electronic equipment consumption (W):

Equipment Type:

Solar exposure of exterior walls:

High (+15%)

Normal

Low / None (-10%)

Relative Humidity:

BTU/h Needed

Do you want to see other calculation tools?

The previous calculation application is a tool to calculate the required BTU/h to correctly choose an air conditioning unit. Just enter the size of the space, orientation, insulation, and number of people, and get the recommended value.

Keep in mind that you can use this tool to know the air conditioning needs of different spaces: living room, bedroom, office, etc.

What is a BTU

The BTU (British Thermal Unit per hour – BTU/h) is a widely used unit in air conditioning to represent the energy a system can extract from or add to the environment per hour. It is a measure of power, indicating the rate at which heat is transferred.

1 kW (thermal) ≈ 3412 BTU/h
1 BTU/h ≈ 0.293 W

How the air conditioning calculator works

The BTU/h calculator allows estimating the cooling power needed to efficiently cool a room. The operation is:

User enters data such as:
- Size and height of the room.
- Number of occupants.
- Type of activity (sedentary, light, or intense).
- Wall insulation
- Specific conditions (windows, solar exposure, humidity, electronic equipment).
A thermal base in BTU/h is calculated according to the volume of the space (m³ × 160).
Additional adjustments are added for:
- Extra occupants.
- Window surface and type of glass.
- Electrical consumption of equipment.
- Solar exposure.
- Relative humidity.
The result is also shown in other units:
- kW (1 BTU/h ≈ 0.000293071 kW).
The calculation detail and a summary of applied adjustments are displayed.

It should be understood that we are calculating BTU/h per m2 in a simplified way for individual air conditioning units. For professional calculations, it is necessary to go to specialized air conditioning programs such as EnergyPlus, ClimCalC Dimension (Isover), Coolselector® 2 (Danfoss), etc.

Calculation elements and their justification

Volume of the room
- Base formula: volume (m² x m) × 160

Reason: It is estimated that a volume of 1 m³ requires approx. 160 BTU/h for efficient cooling. It is an indicative average used in residential air conditioning.

Additional occupants
- Considered only from the 2nd occupant, as the first is already included in the base calculation.
- Multiplied by a BTU/h factor according to the type of activity:
  - Sedentary: 450 BTU/h
  - Light: 600 BTU/h
  - Intense: 900 BTU/h

Reason: People generate body heat that must be compensated with air conditioning.

Type of wall insulation:
- Poor / No insulation: +20%
- Normal / Average: 0% (no change)
- Good / Medium insulation: -10%
- Very good / High: -20%
- Excellent / Passivhaus: -30%

Reason: Insulating materials in walls act as a barrier that hinders heat transfer. In summer, the heat from the sun and the outside environment tries to penetrate the house through the walls, roof, and windows. In winter, the heat generated inside the house tries to escape outside. Insulation minimizes this flow.

Window surface
- Multiply the area in m² by a BTU/h factor according to the type of glass:
  - Single glass without curtains: 750
  - Single glass with curtains: 500
  - Double low-emissivity glass: 250

Reason: Windows are a significant source of heat gain, especially if exposed to the sun.

Electronic equipment
- Total consumption in watts is multiplied by a factor:
  - Home/office: 2.5 BTU/h per W
  - Industrial/commercial: 3.8 BTU/h per W

Reason: Equipment generates heat during use and requires more cooling.

Solar exposure
- Affects the total result:
  - High: increased by +15%
  - Low: reduced by -10%
  - Normal: no change

Reason: Walls exposed to the sun increase the thermal load of the room.

Relative humidity
- Affects the total calculated:
  - Medium (40–60%): +5%
  - High (>60%): +10%
  - Low (<40%): no adjustment

Reason: With higher humidity, the system must work harder to dehumidify, in addition to cooling.

Unit conversion
- BTU/h: British Thermal Units per hour (international standard for cooling/heating capacity).
- kW: energy in kilowatts (official SI unit for power).
  - kW = BTU/h × 0.000293071

Reason: Displaying the 2 units allows comparison with equipment catalogs, which usually indicate power in any of these.

Pre-calculated examples of BTU/h by surface

Below, we offer you a quick table with approximate calculations of BTU/h per m2 of rooms for one person, with normal qualities and ceilings of 2.5 m high:

Room (m²)	BTU/h	Watts (W)	Kilowatts (KW)
10	4000	1172	1.17
12	4800	1407	1.41
15	6000	1758	1.76
18	7200	2110	2.11
20	8000	2345	2.34
22	8800	2579	2.58
25	10000	2931	2.93
30	12000	3517	3.52
35	14000	4103	4.10
40	16000	4689	4.69

🟧 If you have any other questions about how to calculate the BTU of the air conditioning, you can contact us from the contact section at the bottom of the page.

Frequently asked questions about BTU/hrs for air conditioning – FAQ

What is BTU/h in air conditioning?

BTU/h (British Thermal Unit per hour) is a unit that measures the cooling or heating power a system can provide or extract from the environment per hour. It is commonly used to express the capacity of air conditioning and heating equipment.

Are BTU/h and kW the same?

No. BTU/h measures thermal energy transfer rate (cooling/heating capacity), while kW (kilowatt) is the official SI unit for electrical power (how much electricity is consumed) or thermal power. They are related by a conversion factor (1 kW ≈ 3412 BTU/h), but they represent different aspects of energy.

How do I calculate the required BTU/h according to surface?

A common rule of thumb is about 400 BTU/h per m²; for very sunny rooms, it might increase to around 520 BTU/h per m², but other factors must also be considered for an accurate calculation.

How to calculate BTU/h from cubic meters?

Multiply the volume (m³) by 160; for example, 50 m³ × 160 = 8000 BTU/h.

What additional factors should I consider in the calculation of BTU/h?

You must include: number of people (approx. 450 – 900 BTU/h per person depending on activity), watts of electrical equipment (~ 2.5 – 3.8 BTU/h per W), solar orientation, number of windows, type of wall insulation, etc.

How do I convert electrical watts to BTU/h?

Each watt is approximately equivalent to 3.41 BTU/h (1,000 W ≈ 3412 BTU/h).

Is official registration required for equipment with a certain amount of BTU/h?

In Spain, equipment with more than 18,000 BTU/h (≈ 5 kW thermal) must be registered according to regulations.

Why is it important to properly size an air conditioner?

An oversized unit cools quickly but may not dehumidify well, leading to a clammy feeling. An undersized one consumes more energy trying to reach the desired temperature and does not cool effectively, leading to discomfort and higher bills.

What information do I need to calculate the electrical consumption of my appliances?

You need to know the power of the appliance, which is usually indicated on a plate on the back or bottom of the device, expressed in watts (W). You should also estimate the number of hours it is used each day.

Where can I find the power of an appliance?

The power of an appliance is usually indicated on a plate located on the back, bottom, or side of the device. This plate shows technical data such as voltage (V), current (A), and power (W).

What is the difference between watts (W) and kilowatt-hours (kWh)?

Watts (W) represent the power an appliance consumes at a given moment, while kilowatt-hours (kWh) represent the amount of energy consumed during one hour of continuous operation. One kWh equals 1000 watts consumed in one hour.

How does usage time affect the electrical consumption of an appliance?

Usage time directly influences the total consumption. Although an appliance may have low power, if it is in operation for many hours a day, its accumulated consumption will be greater than that of another with higher power but used only a few minutes a day.

How is the monthly cost of an appliance’s consumption calculated?

First, calculate the daily consumption in kWh by multiplying the watts per hour by the hours of use and dividing by 1000. Then multiply that value by the days of the month and by the contracted kWh price to obtain the approximate monthly cost.