What size air conditioner do I need?

Fast read

To ensure that an air conditioner works efficiently, it must be sized correctly. Undersizing the system can result in high energy bills and frequent repair and maintenance costs.

On the other hand, oversizing can lead to wasted energy, increased costs, and moisture build-up in humid environments.

The easiest way to determine the appropriate size of a heat pump is to get an energy audit or work with a trusted professional who will perform a blower door test and a Manual J Load Calculation based on data such as the climate of the city.

Other factors to consider when sizing a heat pump include the average low and high temperatures for each season, the size of the rooms to be heated, the number of people in the home, the efficiency of insulation, the type of windows, and the weather in the surrounding environment.

How to choose the right size air conditioner for your home?

It might seem like the size of your air conditioner system isn’t so important, as long as it is somewhere in the right direction. Well, this is plainly wrong. 

Oversizing or under-sizing the system may cost you more than you expected to pay in the long run. Selecting the right air conditioner is more than just a decision about comfort; it’s a choice that impacts energy efficiency, your power bill, and the longevity of your system. In this FAQ  we’ll dive into the world of air conditioner sizing and explore the consequences of choosing the wrong size.

Understanding kilowatts (kW)

In Australia, air conditioner sizes are commonly measured in kilowatts (kW), representing the cooling or heating capacity of the unit.

  1. Small Rooms (up to 20 square metres): 2-2.5 kW
  2. Medium Rooms (20 to 40 square metres): 2.5-5 kW
  3. Large Rooms or Open Floor Plans (40+ square metres): 5-9 kW or more

Factors to consider when sizing your air conditioner

  1. Room Size: Measure the length and width of the room and multiply to find the square metres.
  2. Climate: Depending on your location in Australia, you may need to adjust the size.
  3. Insulation, Windows, and Construction: Consider the efficiency of your home’s insulation and windows.
  4. Occupants and Ceiling Height: More people and taller ceilings require more cooling.
  5. Sunlight Exposure: North-facing rooms with large windows may need more cooling capacity.
air conditioning units
It’s important to size an air conditioner system correctly, especially when the system has multiple outdoor units

Questions to ask

  • What are the average temperatures for each season?
  • How many rooms are you planning on heating?
  • Will there be a big open space? 
  • How much direct sunlight will the area you are heating receive? 
  • Will you be primarily using the system for heating or cooling? 
  • Are your windows single or double-glazed?
  • Do you have awnings over your west and north-facing windows?
  • How old is your house, and how efficiently insulated is it? 
  • Do you have a solar system to help power the air conditioner?
  • How many people live in your home? 
  • How many heating and cooling zones do you need?

What happens if you get the wrong size?

Oversizing or under-sizing the air conditioner system may cost you more than you expected to pay in the long run.  This is because choosing the incorrect size can have a number of negative consequences:

Too large

Most outdoor air conditioners have variable-speed motors. This means they adjust their heating or cooling based on the outdoor temperature. If sized correctly instead of turning on and off constantly they can provide a comfortable and constant temperature. The problem is, if you oversize the system, it can cause the system to turn on again and off regularly, which is precisely what you don’t want. This becomes even more of a problem in humid parts of Australia since the air conditioner also acts as a dehumidifier, pulling moisture from the air. If the air conditioner is too big it can cool the room too quickly without effectively controlling humidity, leading to a damp environment

Too small

A unit that’s too small will run continuously, trying to reach the desired temperature. This can lead to higher energy bills and potentially premature failure of the system, not to mention a room that’s never quite cool or hot enough. In this instance, the money you save by getting a smaller and cheaper unit will be lost in higher electricity bills after only a year or two. Furthermore, since the system has to work harder, it also can lead to higher and more frequent repair and maintenance costs. 

couple enjoying the air conditioner

The easiest way to determine what size air conditioner system you need is to either get an energy audit or work with a trusted and reliable professional to develop your required heating and cooling energy. It’s all about the cubic meters of space that need to be heated or cooled – as well as the unit’s position, the height of the rooms and the building of the home or business. 

If this calculation is undertaken correctly, a qualified installer will come to your home and perform a blow door test. Along with the blow door test, other data like your city’s climate will be analysed to produce a Manual J Load Calculation. This is the industry standard for sizing an HVAC system. 

Ensuring you find the right-sized air conditioner technology air conditioner for your home is very important to get an enjoyable and affordable result. It will ensure you can achieve a constant and comfortable temperature for your home in summer and winter. There are plenty of online calculators and trustworthy local installers who can ensure you get the perfect size. Once you know what size you need, the rest of the purchase process is easy. 

So how do I find the right size air conditioner for my home?

Finding the right air conditioner size for your Aussie home is about more than just beating the heat. It’s about creating a comfortable environment, being energy-efficient, and making a wise investment for the long term. So as you can see, it’s not that simple and that’s why we say to get professional help.

With the wrong size, you could end up paying more on energy bills, face a shorter lifespan for your unit, or just never quite feel comfortable. By understanding the factors involved and consulting with a professional, you can enjoy a perfectly cool summer and a cosy winter, and if you power the system via solar you get the best environmental and financial outcome.

So, whether you’re braving the scorching heat in Perth or facing a more temperate summer in Melbourne, the right air conditioner size will make all the difference. Here’s to a cool and comfortable home, tailored just for you, down under!

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