What cooling load does my home need for ducted air conditioning?
Cooling load is the amount of heat your home gains on a hot, humid day, and the system has to remove it. Floor area is the starting point, but it is only a rough guide. Two houses of the same size can need very different capacity.
The things that change the number are ceiling insulation, wall insulation, ceiling height, window size and glazing, how much afternoon sun the west side cops, roof colour, and how many people live there. A shaded, well insulated brick home needs less than a tin-roofed place with big west-facing glass. On the Sunshine Coast, humidity adds to the load as well, so the system also has to dry the air, not just cool it.
Is 12.5kW or 14kW ducted enough for my home?
For a typical family home, yes. We add up the heat load of every room on a zone at about 150 watts per square metre, then size the system at about 70% of that total, because the zones are never all running flat out at the same time. In practice a 12.5kW system suits 5 zones: four bedrooms plus an open kitchen, living and dining area, roughly 120 square metres of zoned rooms. A 14kW suits 6 zones: the same again plus a media room or similar, roughly 130 square metres. What counts is the rooms on zones, not the full footprint. A garage, a covered patio or a rarely used room may not count.
A 14kW unit is not always better than a 12.5kW unit. If the house is well insulated and shaded, 12.5kW may do the job comfortably. If you have high ceilings, lots of glass, an open plan living area or a poorly insulated roof, 14kW or even 16kW may be the better call. Treat these figures as a rule of thumb. They are not a quote.
What happens if the ducted system is too big or too small?
A system that is too small runs flat out on hot afternoons and still struggles to hold temperature. It wears harder and the far rooms never quite get there.
A system that is too big is not a safe choice either. It reaches the set temperature fast, switches off, then starts again. That short cycling can leave the air clammy, which is a real problem in Queensland humidity. It can also cost more to run and make more noise at the vents. The aim is the smallest system that handles your hot days properly.
Do zones and the return air grille affect the size I need?
Yes. Zoning lets you cool only the areas you are using, such as the living space during the day and the bedrooms at night. Zone controllers like AirTouch 5 manage this. The system still needs to be sized for the load it will carry when most zones are open, and the ducting has to be designed so air is not forced through too few outlets.
Return air matters too. A ducted unit needs enough return air to breathe. As a rule of thumb, Delta Temp uses a 900 x 500 return grille for 10 to 14 kW systems, and a 900 x 550 grille for 16 kW and above. If the return is too small, the system gets noisy and loses performance, no matter how well the unit was chosen.
How does Delta Temp work out the right ducted size?
We do not size a ducted system from a phone call or a floor plan alone. We come out and do a free site inspection first. We look at the roof space, insulation, ceiling heights, windows, orientation, where the unit and ducts can go, and how you actually use the house.
After the inspection, the quote is fixed, so the figure does not drift once the job starts. The final cost depends on the system size and brand, the number of zones, the ducting and return air layout, and how easy the roof space is to work in. We install brands including Fujitsu and Hisense, and installations carry a 10 year workmanship warranty. Manufacturer warranties are 5 years for Fujitsu and 7 years for Hisense, parts and labour. Delta Temp is QBCC licensed and ARC authorised, and we service the Sunshine Coast from Caboolture to Noosa. Finance is available through humm for approved applicants. To book an inspection, call 1800 335 828.
