Stag Electrical

How Much Power Do I Need?

When considering an air conditioning unit, the first thing to consider is how much power you will need. Air conditioning capacity is measured in BTU (British Thermal Unit) and power output in kilowatts.

Efficiency is measured with a star rating. The efficiency for heating and cooling are rated separately. The more stars the more energy efficient. To compare appliance efficiency the government website can help.

It is important to select the correct size unit for your space.

Selecting the right air conditioner for your space can depend on many factors. Let us help you decide by breaking them down. 

Air Conditioner Size

How Big Is Your Space?

If the unit is too small, it will not cool efficiently. If the unit is too large it will use excessive power. As a general rule the following table outlines the correct size unit for certain areas. 

Room Area (m2)Air Conditioner Unit Size (kw)
30-45m25 to 6kw
45-65m27 to 8kw

These calculations however can be affected by multiple variables.

Is Your Home Insulated?

A home which is insulated will be able to maintain it’s temperature better than one without. This means a house without insulation need a more powerful unit. 

Without insulation a home can build up 25 to 35 % more heat in summer from the roof alone. To a lesser extent the walls but still 15 to 25 % more heat.

STAG TIP: Ceiling insulation will have the largest impact on the size of the unit you need. If you do not have roof insulation, we recommend installing it. The addition will save you money by being able to purchase a smaller, cheaper air conditioner. Your ongoing running costs will also be lower.

What climate do you live in?

In Australia tropical and sub-tropical areas will generally have a higher demand on the cooling unit. Climate will also play a role in the type of air conditioner that will be most effective. Evaporative systems will be more effective in dry heat while refrigerated will work well even in extreme humidity.

What is the orientation of your house and windows?

The number of windows or skylights in your home and the direction they face can need to be considered. If your home receives a lot of sun throughout the day this could require more cooling compared to darker home. 

What If I Choose The Wrong Size?

Whether it to large or too small, both can have detrimental effects. 


  • The unit will have to run at maximum output
  • The unit will dry the air
  • More wear on the unit
  • Running costs increase


  • The unit will run frequent short cycles. Turning off and one
  • Results in more wear on the system
  • The area will feel to hot and cold as the system quickly cools the space and turns off
  • Power use increase
  • Running costs increase

Other Factors To Consider

-Does your home have window coverings and how effective are they eg block out blinds or sheer?

-The type of lighting in your home and the quantity

-The amount of people in your home

-The type and quantity of ducting

-The type of foundation in your home

-The height of your ceiling

-The type of construction of your home

What Type of Air Conditioner Do I Need?

It is important to understand a few key terms before you select the correct unit.

Reverse Cycle: An air conditioner that offers both heating and cooling capabilities

Inverter: Inverter air conditioners deliver a constant airflow. This allows for better temperature regulation and higher efficiency.

Smart AC: Smart air conditioners connect to your home network. They can control and monitor their output through an app.

1. Split System

Split system air conditioners consist of two units. One is installed outside and the other inside. They are generally the most effective and best suited to use for a single area.

The units are usually quieter and more powerful while also being very efficient. 

Suitable when heating large rooms or even a whole residence. 

Split system air conditioners will often have special features such as WiFi and air ionisers. Motion sensors can also be included which increase air quality and efficiency.

Split systems require the professional installer to make alterations to the home. As a result these systems are best suited to home owners. 

Air Conditioning Size

2. Ducted Split System

A ducted split system is where the one unit will serve an entire home or area. It can be zoned to cool/heat only certain rooms by blocking air flow. This reduces the power output of the system.

3. Ducted Evaporative System

The evaporative system is also ducted throughout the home. It is a lower price point for purchase. They are not as effective in cooling as the split system, especially in humid weather. The evaporative system works by using water to cool the air. Evaporative systems do not provide heating.  

4. Window Wall

Window or wall air conditioners are a more affordable option compared to split system while still delivering good results. 

Window/Wall air conditioners work best for small or confined spaces. When used in the correct capacity window air conditioners can be very efficient and effective.

Unlike like a split system, a window air conditioner install does not require professional installation.  If you wish to install these units to vent through a wall, professional assistance is required.

Window/Wall air conditioners can also feature extras like timers, remote control and air ionisers. Window air conditioners will always require a window open. These are available with built in insect guards. 

5. Portable

Portable systems are ideal for single room use or to move between rooms. They are also great for anyone in rental accommodation as they require no alteration to the property. They are a low cost option to purchase. Portable units are not as effective in their operation.

Most portable air conditioners have features like a remote controls and timer. Some will have omnidirectional louvres which help spread cooled air effectively

Extra functions may be available on high end products such as:

· Dehumidifiers- Lowers humidity in the room for improved comfort

· Slide out chassis- easy installation

· Mosquito Traps

· Air Filter- Reduces smoke, germs and odours in the air 

Can I Run An Air Conditioner Off A Generator?

To run an air conditioner off a generator you need to select a generator that is capable of producing the power your unit will need.  

Two power requirements of the air conditioning unit you need to know:

The starting wattage and the running wattage. 

An air conditioner requires more power to start up than it does to run. Some units by as much as an extra 1,000 watts (1kW). You should also allow for any other power drain on the generator. 

A small air conditioner can often be run off a 2kW portable generator. A large air conditioner will need substantially more power. Best to consult with your electrician as to the suitability. 

Air Conditioner Size
Feeling overwhelmed? We understand. A lot of factors come in to play when selecting the correct size Air Conditioning system for your home.
Having a qualified Electrician do a free assessment of your home is the best way to ensure you select the correct unit. They have the experience to factor in the features of your home to match you with the correct system.

Call Stag Electrical for a free assessment and quote today by clicking below. You can also check out our YouTube or Facebook page for more blogs and Stag Tips.

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