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As a rough starting point, a bedroom or small room up to about 20 square metres usually needs a 2.5 to 3.5kW split system, and a bigger living, dining or open-plan area up to about 35 square metres usually needs 5 to 7kW. Those numbers shift once you factor in ceiling height, insulation, and how much north-facing glass the room has, which is why the same advertised unit can cool one lounge room beautifully and leave another one struggling. Getting the size right matters more than most people expect. A unit that’s too small runs constantly and still can’t quite hold the room at temperature on a hot day, and a unit that’s too big cools the room down fast without properly pulling the humidity out of the air, so it can still feel clammy even once the number on the remote looks right. We install split systems Geelong wide, and correct sizing is one of the first things we check before recommending anything.
The general sizing numbers to start from
These figures come from the sizing guide our technicians use every day on the tools, and they’re a genuinely useful starting point before you go any further.
| Room type | Approximate floor area | Typical capacity |
|---|---|---|
| Small bedroom, nursery or home office | Up to 20m² | 2.5kW |
| Larger bedroom or a compact living room | Up to 20m², simpler layout | 3.5kW |
| Open-plan living, dining and kitchen | 20 to 35m² | 5 to 7kW |
For anything bigger than around 35 square metres, or an open-plan space that runs longer than that, it’s worth having someone measure it properly rather than guessing, because a few extra factors start to matter more than the floor area alone.
What changes the number for your actual room
Floor area gets you close, but a few things in the room itself can push the right capacity up or down within these bands.
A high or raked ceiling means more air volume for the same floor space, so a room with a cathedral ceiling often needs more capacity than a standard 2.4 metre ceiling of the same size. An older, poorly insulated home loses cooled or heated air faster than a newer, well-insulated one, so the unit has to work harder to hold the temperature. A room with a lot of north or west-facing glass takes on far more heat through the afternoon than a shaded, south-facing room the same size, which is one of the most common reasons a “correctly sized” unit still struggles in summer. Open-plan spaces that flow into a kitchen or hallway effectively cool a bigger area than their own floor plan suggests, since warm air from cooking and adjoining rooms drifts in. None of this means the sizing chart is wrong, it just means it’s a starting point rather than the final answer for your specific room.
Why getting the size wrong costs you either way
People sometimes assume bigger is simply better, but an oversized unit isn’t a safe bet. It cools the air quickly and switches off before it’s had time to properly remove the moisture, so the room can feel cool but slightly damp, and the compressor cycles on and off far more often than it should. That extra cycling uses more electricity than a correctly sized unit running steadily, and it puts more wear on the parts that fail first. Going too small has its own cost. An undersized unit runs almost non-stop through summer, never quite reaching the set temperature on the hottest days, and that constant strain shortens how long it lasts before something needs replacing. Either way, the household ends up paying for it, in comfort, in the power bill, or in an earlier repair call than they should have needed.
A Newtown lounge room, worked through properly
A weatherboard in Newtown had its lounge and dining opened up into one 28 square metre space during a renovation, with a wide bank of north-facing windows looking onto the garden. Going purely off the floor area, 5kW looked like the obvious choice. But by half past five on a January afternoon, with the kids finishing homework at the dining table and dinner starting on the stove, that room is taking on a lot more heat than a shaded room of the same size ever would. Our technician sized it toward the top of the 5 to 7kW band instead, accounting for the glass and the cooking heat, and the difference shows up exactly when it matters most, at the end of a 35 degree day with the whole family home at once.
Get the right size confirmed before you buy
If you’re about to replace an old unit or fit out a new room, it’s worth having someone measure the actual space rather than working from the box at the hardware store. We’ll assess the room, the glass, the ceiling height and how the space is actually used, and back the install with our 7 year workmanship guarantee and up to 7 years on the product itself. Call Too Hot To Handle on 0480 005 425 or email info@toohottohandle.com.au and we’ll help you get the size right the first time.
FAQ
What size split system do I need for a bedroom?
Most bedrooms up to about 20 square metres are comfortable with a 2.5 to 3.5kW split system. A larger bedroom, a north-facing room, or one with a raised ceiling can push that toward the higher end of the range, so a quick on-site check is worth it if your room is on the bigger side.
What size split system do I need for an open-plan living area?
Open-plan living, dining and kitchen spaces between 20 and 35 square metres typically need 5 to 7kW. Anything larger, or a layout with a lot of north or west-facing glass, usually needs an actual assessment rather than a floor-area estimate.
Can a split system be too big for a room?
Yes. An oversized unit cools the room quickly but shuts off before it’s properly removed the humidity, which can leave the space feeling damp even at the right temperature, and the extra on-off cycling uses more power and wears the unit faster than one that’s sized correctly and runs steadily.
Does a bigger split system cool a room faster and better?
It cools the room faster, but faster isn’t the same as better. A unit sized correctly for the room holds a steady, comfortable temperature and properly dehumidifies the air, while an oversized one gets there quickly and then stops, which is a less comfortable result overall.
Should I get a technician to measure before buying a split system online?
It’s worth it any time the room isn’t a simple, small, well-shaded space. Ceiling height, insulation, window size and orientation all change the right capacity, and a five-minute on-site check avoids paying for an install that never quite gets the room comfortable.
