BTU, Kilowatts or Horsepower? Air Conditioner Sizes Explained

In Australia, the best way to compare air conditioner capacity is in kilowatts (kW). Some products are still advertised in BTU (British Thermal Units) or horsepower (HP), which makes it hard to compare like with like. As a guide, 1kW is about 3,412 BTU per hour, while horsepower describes the motor rather than how much heating or cooling the system delivers.

Kilowatts

Australia uses the metric system, so the correct way to express the output of a split system air conditioner is in kilowatts. Australian energy rating labels show the cooling and heating capacity in kW, which makes kW the easiest figure to compare.

BTU

A British Thermal Unit (BTU) is the amount of energy (heat) needed to raise the temperature of one pound of water by one degree Fahrenheit. Air conditioner capacity in BTU is usually given per hour.

The United States still uses imperial measurements such as feet, inches and Fahrenheit, so some air conditioners arrive in Australia with promotional material that advertises their output in BTU, even though Australia began changing to the metric system in 1970.

If a product is only advertised in BTU, ask for its capacity in kW and check its details on the Energy Rating database. A supplier that has not updated its material for the Australian market may also be less prepared when it comes to after sales service.

BTU to kW conversion

To convert, divide the BTU per hour figure by 3,412.

Horsepower

A horsepower rating is the rated capacity of a motor. It is an unreliable way to compare air conditioners because it does not translate to the energy efficiency ratio (EER) or coefficient of performance (COP) a system achieves.

For example, a 2.5HP motor in one brand might give an output of 5.4kW, while a 2.5HP motor in another brand might give 6.4kW, a difference of 1kW. Because one brand can achieve a higher output than another with the same size motor, horsepower is not a reliable measure for comparing air conditioners.

What size air conditioner do I need?

The right capacity depends on the size of the room, ceiling height, insulation, windows, which way the room faces and how you use the space. An undersized system will struggle on very hot or cold days, while an oversized one costs more than it needs to. Our heatload calculator is a good starting point, and our team can confirm the right size for your home. You can then compare models in our split system, multi-split and ducted ranges.

How to calculate EER and COP

Read how to read a split system energy label to learn how the energy efficiency ratio (EER) and coefficient of performance (COP) are calculated and compared.

Frequently asked questions

How many kW is 12,000 BTU?

12,000 BTU per hour is about 3.5kW. To convert BTU per hour to kW, divide by 3,412.

What does a 2.5HP air conditioner mean?

It describes the rated capacity of the motor, not the heating or cooling output. Two 2.5HP systems from different brands can have quite different outputs, so compare kW instead.

Is kW input or output on an air conditioner?

Both are used. Capacity is the heating or cooling output in kW, while power input is the electricity used in kW. Divide output by input to work out efficiency.

What size air conditioner do I need for my room?

It depends on the room size, ceiling height, insulation, windows and orientation. Use our heatload calculator as a starting point and ask our team to confirm the right size.

Related guides

Keep reading with these related EZYAIR guides:

• How to Read a Split System Energy Label
• Zoned Energy Rating Labels (ZERL) for Air Conditioners
• What Is a Split System Air Conditioner?
• What Is an Inverter Air Conditioner?
• What Are the Best Air Conditioner Brands in Australia?

Talk to EZYAIR

Ezy Air Conditioning & Heating Pty Ltd (EZYAIR) has been helping Melbourne homes and businesses with heating and cooling since 2007. If you have a question about choosing the right size air conditioner or would like a quote, contact our team or call 1300 399 247, Monday to Friday, 9am to 5pm.

Our head office and display centre is at 49 Huntingdale Rd, Burwood VIC 3125.