In Queensland we all love our air con and having the right size air conditioning system can make or break the experience. There are many factors that will influence the size of air conditioner you need to deal with the local climate, how you use the space, how many windows and any sun exposure can all influence your air conditioning unit sizing.
Energy efficiency should always be at the top anyone’s list when choosing a new air conditioning unit, having the correct heating and cooling capacity will have a great impact on this. Over its useful working life the right sized air conditioner can save you a lot of money. It’s always best to consult an expert.
How do I size a room for an air conditioner?
The simple answer here is to have an expert come out and assess the area to that requires air conditioning to make sure you get the right air conditioner.
You’ll have the benefit of years of experience to help you choose the correct air conditioner capacity and then enjoy years of economical comfortable use.
We use an equation to calculate the air conditioning capacity requirements which is – floor area in square meters x a heat load in watts per square meter. As a rough guide for our local climate we like to use a heat load of 0.16 kW per square metre for an average space – with normal heat load.
This means a normal bedroom which is 4m x 4m = 16 sqm x 0.16kW / sqm = 2.56kW. So for this size room you would be looking for an air conditioner with a cooling capacity of 2.5kW
For larger rooms like a lounge which was 8m x 5m = 40sqm x 160w / sqm = 6.4kW. So for this sized room would be looking for an air conditioner with a cooling capacity of 6/7.0kW.
Factors that will impact the size of the air conditioner you need
Having the right sized air conditioner can deliver considerable energy savings. There are many factors that can influence the size air conditioner you need. Some of these factors include:
- Ceiling height. The higher the ceiling height in the room the larger the volume of air in the room. The greater the volume of the room the more air the air conditioner needs to cool. We would use a higher heat load for a room with high ceilings – like 0.18kW or 0.2kW per sqm.
- Use of the room. If you have a room which has heat generation sources like appliances eg. ovens or which routinely has a high density of people in it eg. meeting room, dining room etc. then those rooms will have a higher heat load than normal – requiring a more powerful air conditioner.
- Direct sunlight. Direct sunlight onto the wall or window of a room creates heat. This heat needs to be dealt with by your air conditioner. The most energy efficient way to deal with sunlight generated heat is to prevent it from entering the room in the first place – ideally with external shading or insulation.
- Insulation. There are two main ways heat makes it way into an interior space – either through the walls or through the ceiling from the roof space. Uninsulated roof spaces can be very hot indeed transmiting significant heat into a room. This can be managed through insulation – preferably a heat blanket under the roof material (reducing the heat entering the roof space) or on ceiling insulation (reducing the amount of heat being transmitted from the roof space into the living space). Another way of reducing the heat transmitted from your roof space into your living space is to ventilate your roof space – either by a powered or non-powered roof ventilator – these can dramatically reduce the amount of hot air in your roof space.
All of these factors need to be taken into account when deciding – what size air conditioner do i need?
What happens if my air conditioner is too small?
There’s no substitute for getting things just right, an undersized air con will struggle to maintain your chosen temperature, working harder for longer trying to achieve the desired room temperature.
When your air conditioner works harder than it needs to, it consumes more energy than necessary. This can result in higher energy bills, decreased reliability, and potentially a shorter lifespan, ultimately raising its overall lifetime ownership costs.
What happens if my air conditioner is too big?
Bigger is not always better. In Queensland the humidity can make life really difficult. Your air conditioning system is designed to cool a room gradually allowing time to reduce both temperature and humidity. An oversize AC may not effectively reduce that excess humidity, leaving the room still ‘feeling’ warm even though the set temperature has been achieved.
An oversized air con will cost more to purchase and install as well as costing more to run – further increasing the total lifetime cost of ownership.
Is it better to oversize or undersize an air conditioner?
When choosing a new reverse cycle air conditioner, it’s really important to have the right sized air conditioner. An air conditioning system that matches the space and conditions it has to work in will be more reliable and keep energy consumption to a minimum saving you money.
A split system air conditioner that’s either over or under sized can use more energy than necessary whilst working outside of its design conditions and can also cause reduced reliability with the risk of increased repairs, costing you more money.
The right size air conditioner can deliver significant energy savings when compared to an air conditioner that is incorrectly sized
Split System air conditioner size chart by room size
| Room Type | Typical Room Area – Square Metres | High Wall Split Capacity |
| Small Bedroom | 14 sqm | 2.5 kW |
| Large Bedroom | 20 sqm | 3.5 kW |
| Kitchen / Dining Area | 40 sqm | 6 kW |
| Open plan Living / Dining | 50 sqm | 8.0 kW |
High Wall Split system air conditioners are best suited to servicing a single room only. Depending on the location of the indoor unit you may be able to get cooling in a small number of adjacent rooms.
A single split systems is not suitable for cooling an entire house – even if the nominal capacity of the system is adequate. This is because the fan on the indoor unit is not going to be able to distribute air and regulate temperature across multiple rooms.
Looking for more information on split air conditioning units? Learn more about our range of split system air conditioners & installation services.
Ducted air conditioner size chart by house size
| Number of Bedrooms | Number of Zones | Ducted AC Capacity |
| 3 | 4-5 | 10-12kW |
| 4 | 5-6 | 12-14kW |
| 5 + | 6-8 | 16kW + |
Ducted air conditioning systems are capable of cooling or heating multiple rooms at the same time. Modern air conditioners and zoning systems can offer highly efficient solutions, delivering more precise temperature control when compared to older units. The correct use of zoning systems and a correctly sized unit can help reduce the initial investment as well as reduce the overall running costs, allowing you the option of just to cool the areas you use.
Looking for more information on ducted air con? Learn more about our range of ducted air conditioners & installation services here.
Portable air conditioners
We get lots of queries asking about portable air conditioners.
There are three main draw backs of portable air conditioners:
- Noisy. A portable air conditioner is an all in one air conditioner. So this means the noisy part – the compressor – is in the room with you.
- Negative pressure. Unlike split system air conditioners which exhaust their heat through the outdoor unit a portable air conditioner exhausts its heat through a exhaust hose that goes through a vent mounted in the rooms window. It takes conditioned air from the room and vents that out the window which does two things:
- Reduces the efficiency of the air conditioner
- Reduces the pressure in the room – meaning whenever you open the door to the room it will draw in hot air from outside.
- Water needs emptying. A portable air conditioner takes moisture out of the air like any other air conditioner – but it doesn’t have a drain line. This means it is stored in a reservoir in the air conditioner. Often these reservoirs are self evaporating – but in high humidity conditions they will need emptying.
Get a free quote on air conditioning installation in Brisbane
Whether you’re looking to install air conditioning in your home for the first time, or want an upgrade on an existing air conditioning unit, we’re here to help. Contact us for a free quote on air conditioning installation in Brisbane.