28/10/2025
What Sized Air Conditioner Do I Need?
When it comes to choosing an air conditioner for your home, size does play a factor. Pick a unit that’s too small, and you’ll struggle to keep comfortable. Pick one that’s too large, and you may find yourself with uneven temperatures and a larger-than-expected electricity bill. Regardless as to whether you’re purchasing a split system air conditioner, or a reverse cycle ducted air conditioner, knowing the right sized system is important. So, how do you know what sized air conditioner you need? Let’s break it down.
The Problems with an Air Conditioner that is Too Small
An air conditioner that’s too small for your home will constantly be playing catch-up. Instead of delivering consistent, comfortable airflow, it will often:
- Struggle with airflow: A smaller unit simply can’t push enough conditioned air throughout your home. You may find that it only cools or heats one or two rooms effectively, leaving the rest of the house uncomfortable.
- Operate at 100% capacity: Because the unit is working harder than it should, it’s often running flat-out all day. This constant strain increases wear and tear, shortening the system’s lifespan.
- Deliver patchy comfort: Even in the rooms it does reach, the air may feel weak, inconsistent, or slow to adjust to your desired temperature.
In short, going too small may seem cheaper upfront, but it almost always costs more in the long run—both in repair bills and in comfort. The right sized air conditioner will provide comfort in a variety of seasons.
The Problems with an Air Conditioner that is too Large
On the other end of the spectrum, bigger isn’t always better. An air conditioner that is too large or too powerful sound like a safe choice, but it can create problems of its own:
- Draughts and hot/cold spots: A unit that’s too powerful will blast cold or warm air into the space too quickly. This often creates uneven temperatures—some areas become too cold, while others remain untouched.
- Short cycling: Because the unit cools or heats a room so rapidly, it may shut off frequently. This constant on-and-off cycle doesn’t give the air time to circulate evenly, leaving rooms feeling inconsistent.
- Higher energy bills: Larger systems draw more power. Even if they’re only running in short bursts, the sheer capacity of the unit means your electricity bills can climb significantly.
Not only is oversizing inefficient, but it can also make the home less comfortable overall.
Why a Tailored Heat Load Assessment is Essential
Every home is different. The right air conditioner for a five-bedroom brick home in Canning Vale will not be the same as what’s needed for a two-storey townhouse in Fremantle. That’s where a tailored heat load assessment comes in.
At Ford & Doonan – Perth’s ducted air conditioning experts since 1985, with over 40 years of experience, we don’t guess when it comes to system sizing. Instead, we carry out a detailed site inspection and heat load calculation. This process looks at:
- How you use your home: Do you want the entire house at the same temperature, or just the main living areas?
- Heat ingress areas: Large windows, skylights, and roof orientation can all influence how much heat enters a room.
- Room layout and airflow: We consider how air will travel through each space, ensuring consistent comfort across the home.
- Optimal positioning: The placement of outlets, the indoor unit, and the outdoor condenser all play a role in how effective your system will be.
By carefully assessing these factors, we can recommend a system that’s perfectly matched to your home—not too small, not too large, but just right. If you’re looking for approximate, ball park pricing, try our air conditioner size calculator below.
What if I am Building a New Home?
Congratulations on your new home! Opting for the right air conditioner for your new home is just as important as if it was for an existing home. Ford & Doonan work with a range of WA’s most recognisable residential and light commercial builders. Our Builders Direct division specialises in under construction single and double storey homes. Here are a few items to discuss with your builder during the construction stage:
- Outdoor unit: Ensure there is enough space down the side or at the back of your home for the outdoor condenser unit. A good rule of thumb is at least 1.5 meters from the boundary fence, and 1 meter away from any gas hot water system
- Return air grille: Discuss with your builder about framing out for the return air grille box and filter assembly.
- Controller location: If you’re opting for a reverse cycle ducted air conditioner, discuss with your builder about running an additional empty conduit in a location where you’d like the controller to go
The Best Approach: Professional Guidance
While online calculators and “rule of thumb” guides can give you a rough idea of system size, nothing replaces a professional assessment. Guesswork almost always leads to wasted money and reduced comfort.
Ford & Doonan offer a range of air conditioners available from industry-leading brands such as Daikin, Panasonic and Samsung.
The best approach is to work with a trusted specialist who takes the time to understand your home and your lifestyle. At Ford & Doonan, we pride ourselves on tailoring every installation to deliver:
- Consistent airflow across all chosen rooms.
- Energy efficiency that keeps running costs low.
- Longevity by ensuring your system isn’t straining or short cycling.
- Comfort that feels natural and evenly distributed.
Meaning you have the right air conditioner size for your home that balances energy consumption, with air flow and the local climate. Understanding your air conditioning needs is important to provide the best heating and cooling for you.
Final Thoughts
When it comes to air conditioning, size and power isn’t just a number—it’s the key to year-round comfort, efficiency, and peace of mind. A system that’s too small, or one trying to do multiple rooms, will be overworked and may underdeliver. A system that’s too large will leave you with draughts, hot and cold spots, and a bigger power bill.
The smartest choice is to book a tailored heat load assessment and site inspection with Ford & Doonan. Our expert team will design a solution that fits your home perfectly, so you can enjoy reliable comfort for years to come.
Ready to find the perfect system for your home? Contact Ford & Doonan today and book your free in-home consultation.
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