Reviewed by Lee Gundenswager (Lead Electrician, Connex Lic #92217) and Darren Standring (Owner). Last updated May 2026.
Choosing the wrong size split system is the most expensive mistake Brisbane homeowners make with air conditioning. Too small and it runs flat-out, never reaches temperature, and dies years early. Too big and it short-cycles — switching on and off constantly, creating humidity problems and uneven temperatures.
We install split systems across North Brisbane every day. Here’s what we’ve learned about getting the size right for Queensland homes.
Why Split System Sizing Matters More Than Brand
Homeowners spend hours comparing Daikin vs Mitsubishi vs Fujitsu. That matters — but a correctly sized budget unit will outperform a premium unit that’s the wrong capacity. Every time.
An undersized 2.5kW unit in a 40sqm living room in North Lakes during a February heatwave will run continuously, spike your power bill, and burn out the compressor within 5-7 years. A correctly sized 7.1kW unit in the same room runs in comfortable cycles, maintains temperature, and lasts 15+ years.
Quick Sizing Guide — Brisbane & North Brisbane Homes
These are starting points based on typical North Brisbane housing stock. Your actual requirement depends on insulation, window size, ceiling height, and sun exposure.
- Small bedroom (10-15sqm): 2.5kW — standard in most Griffin and Mango Hill project homes
- Master bedroom (15-25sqm): 3.5kW — handles the larger bedrooms in Bridgeman Downs acreage homes
- Living room (25-35sqm): 5.0-6.0kW — typical for open-plan living in Kallangur and Petrie
- Large open-plan (35-50sqm): 7.1-8.0kW — common in the two-storey North Lakes and Burpengary estates
- Very large living/entertaining (50sqm+): 8.0-10kW or consider ducted
Factors That Change the Calculation in Queensland
West-Facing Windows
If your living room has large west-facing windows — common in Stafford, Wavell Heights, and Aspley post-war homes — afternoon sun can add 30-50% to the cooling load. A room that needs 5kW with south-facing windows might need 7.1kW with western exposure. External blinds or window film can reduce this significantly.
Insulation (Or Lack Of It)
Older homes across Chermside, Everton Park, and McDowall — particularly the 1960s-70s brick homes — often have zero ceiling insulation. The roof space hits 60°C+ in summer and radiates heat directly into the room below. Adding insulation before installing AC can drop your required unit size by a full step.
Ceiling Height
Standard ceiling height is 2.4m. The Queenslander-style homes in Stafford and Wavell Heights often have 2.7-3.0m ceilings — that’s 15-25% more air volume to cool. Factor this in or your unit will struggle.
Open-Plan vs Closed Rooms
A 5kW unit can cool a 30sqm closed room easily. The same unit in a 30sqm space that opens to a hallway, kitchen, and stairwell is actually trying to cool 60sqm+ of connected airspace. This is the single most common sizing mistake we see in North Lakes project homes — open-plan downstairs areas that need 7-8kW but have a 5kW unit installed by the builder.
What Happens When You Get It Wrong
Undersized Unit
- Runs constantly — never reaches set temperature on hot days
- Power bills 30-50% higher than a correctly sized unit
- Compressor wears out in 5-7 years instead of 12-15
- Uncomfortable — room temperature fluctuates, feels humid
Oversized Unit
- Short-cycles — turns on and off every few minutes
- Never runs long enough to dehumidify properly (critical in Brisbane’s humidity)
- Creates cold spots near the unit, warm spots at the far end of the room
- Higher upfront cost for no benefit
- Increased wear on the compressor from frequent starts
Brands We Install & Recommend for North Brisbane
We supply and install Daikin, Mitsubishi Electric, Fujitsu, and Samsung split systems. All four are reliable in Queensland’s climate. Our recommendation depends on the job:
- Daikin — best all-round. Quiet, efficient, excellent humidity control. Our most-installed brand across Redcliffe and Deception Bay
- Mitsubishi Electric — premium build quality, strong in larger capacities. Popular for master bedrooms and living rooms in Bridgeman Downs and McDowall
- Fujitsu — strong value. Compact indoor units suit homes with limited wall space. Popular across Kallangur, Petrie, and Lawnton
- Samsung — Wind-Free technology is popular with families (no direct cold airflow). Good mid-range option
What a Proper AC Installation Includes
Every split system installation by Connex Electrical includes:
- On-site assessment with correct sizing calculation
- Dedicated electrical circuit from your switchboard (required for units over 3.5kW)
- Indoor unit mounting, outdoor unit positioning, pipework, drainage, and insulation
- Full electrical connection and commissioning
- Manufacturer warranty registration
- Certificate of compliance
We hold both QLD Electrical Licence #92217 and ARC Refrigeration Licence #AU42842 — one team handles the entire job. No subcontractors, no second visit for refrigerant.
Back-to-back split system installs start from $1,120 fully installed. Extended pipe runs from $2,800. Full AC pricing →
Frequently Asked Questions
A standard Brisbane bedroom (up to about 20 square metres) suits a 2.5kW to 3.5kW split system. Larger master bedrooms with lots of glass may need 3.5kW. Correct sizing keeps running costs down — an oversized unit short-cycles and an undersized one runs constantly.
A typical living or family room of 25 to 40 square metres suits a 5kW to 7kW split system. Large open-plan living and dining areas over 40 square metres often need a 8kW+ unit or a multi-head system for even cooling.
As a rule of thumb, allow about 125 watts of cooling capacity per square metre of floor area for a standard Brisbane home. A 20 square metre room needs roughly 2.5kW; a 40 square metre room roughly 5kW. Ceiling height, insulation, window size and sun exposure all adjust this, so a professional assessment gives the most accurate result.
Neither. An oversized unit cools too fast, short-cycles, and fails to remove humidity, leaving the room cold and clammy. An undersized unit runs flat out and never quite cools the room. Matching the capacity to the room is the key to comfort and low running costs.
A back-to-back split system install starts from $1,120 including GST if you supply the unit. Including a correctly sized unit, most single-room splits cost $1,300 to $4,500 installed depending on capacity and brand.
Yes. A split system needs a dedicated electrical circuit and isolator, installed by a licensed electrician, plus refrigeration work by an ARC-licensed technician. Connex Electrical holds both licences and completes the full job in-house.
Need help choosing the right split system? Call Connex Electrical on 0474 207 609 for a free on-site assessment across North Brisbane.