Three Split Systems and Ceiling Insulation Cost Less Than One Ducted System

Ducted air conditioning cost against three split systems

At Going Rate's prices, one ducted reverse-cycle system, installed ($14,000) costs about 4.7 times a single split system, supplied and installed ($2,950). Four splits come in under the ducted price. Three splits cost 63% of it. Add ceiling insulation for the whole home ($3,500) and three splits plus the insulation come to 88% of the ducted price. The money left over would cover about 1.3 times a year of running a ducted system ($1,300).

Three splits cool and heat three rooms. Renew picked a living room and two sleeping areas when it modelled the swap for Environment Victoria, and this comparison assumes the same layout. Hallways, bathrooms and a study stay unconditioned unless doors are left open for the air to drift. A ducted system reaches every room with an outlet. Going Rate's split price is for one typical unit, and a large living-room split costs more, so treat the four-split figure as a guide and expect quotes to vary.

CHOICE's ducted buying guide, updated in December 2025, says a ducted reverse-cycle system costs at least $9,000 for a small house or apartment and can easily reach $15,000 or more for a typical freestanding house. Going Rate's typical price sits inside that range. Melbourne quotes gathered for the 2024 Environment Victoria and Renew report show a similar gap. Whole-home ducted reverse cycle was the most expensive option the report considered, at $12,325 including Victorian Energy Upgrades incentives, while three new splits came to $5,327 to $5,373.

What ducted air costs to run each year

The federal government's energy.gov.au says ducted systems are less efficient than wall units because they use a larger fan and lose energy through the ductwork. Canstar Blue says ducted air conditioners typically cost more to run than split systems. Heating and cooling make up around 40% of household energy use in the average Australian home, according to YourHome.

At Going Rate's prices, a year of running ducted air ($1,300) equals about 9% of the installed price ($14,000), every year the system runs. The thermostat setting moves that figure. YourHome and energy.gov.au both say each extra degree of heating or cooling adds about 5 to 10% to energy use, and a ducted system pays that in every zone left open.

Zoning cuts the waste. A ducted system that conditions only the living areas by day and the bedrooms at night uses less power than one running through the whole house. A split in each used room does the same job by default, because the unit in an empty room is off.

Every ducted system CSIRO tested in new homes failed the leakage limit

CSIRO's June 2024 report, Air Infiltration of New Dwellings in Australia, measured duct leakage in 11 new houses. None of the systems passed the IECC 2021 limit of 0.73 cubic metres an hour per square metre of floor area at 25 pascals. Ducted reverse-cycle systems with a ceiling return averaged 1.40, about twice the limit. Those with the return grille in a wall cavity averaged 4.78, and one of them, at 11.61, was the worst result in the study. Evaporative systems averaged 5.13.

Most of the leaked air ended up outside the living space. In the five systems CSIRO tested for leakage to the outside, 79 to 93% of the leakage was lost directly to unconditioned space, such as the roof space. The owner pays to heat or cool that air and gets no comfort from it.

A new home's star rating misses part of the loss. CSIRO notes that NatHERS counts duct losses while the system runs, but leakage through the ducts when the system is off is not currently considered. The study tested 233 new dwellings built from 2020 onward, and only 11 houses had their ducts tested, so the duct results describe a small sample of new builds and say nothing about older homes.

Ceiling insulation cost belongs in the same budget

Insulating the ceiling ($3,500) costs a quarter of a ducted system ($14,000) at Going Rate's prices. The ducts of a ducted system usually sit in the same roof space the insulation protects, so a poorly insulated ceiling heats the ducts in summer and chills them in winter before the air reaches a room.

YourHome says ducts should be insulated to at least R1.5 with the joints sealed. The NCC 2022 Housing Provisions set a minimum of R1.0 or R1.5 for ductwork, depending on the climate zone and whether the system both heats and cools. For flexible ductwork, the ABCB's explanatory table gives 63 mm glasswool as an example of R1.5. A buyer can ask the installer to put the duct R-value in the quote.

Insulating first lowers the heating and cooling load, which can mean a smaller ducted unit or fewer splits. Victoria now requires it of some landlords. RenewEconomy reported in June 2025 that Victorian rentals with no ceiling insulation must have at least R5.0 installed at the start of a new lease.

Evaporative cooling and ducted heating cost less, and do less

Ducted evaporative cooling ($6,750) costs just under half of ducted reverse cycle ($14,000) at Going Rate's prices. energy.gov.au says ducted evaporative coolers use less than half the electricity of an air conditioner of similar capacity. They only cool, they work best in low-humidity inland regions, and YourHome warns that built-in evaporative systems can raise heating bills in winter because warm air escapes through the ducting. Evaporative systems also had the highest average duct leakage in CSIRO's tests.

Ducted heating on its own ($10,800) costs about 77% of a ducted reverse-cycle system at Going Rate's prices. Pair it with evaporative cooling and the two systems cost about a quarter more than one ducted reverse-cycle system that heats and cools. Environment Victoria and Renew found the average Victorian ducted reverse-cycle system uses less than a quarter of the energy a gas heater uses for the same heat.

Gas ducted heating also needs regular servicing. Energy Safe Victoria says gas heaters should be serviced at least every two years, and that for ducted heaters a carbon monoxide test should be done at the vents in every room. A ducted gas heater service ($490) every two years adds to the running cost of a gas system.

Victoria's rebate pays the same for four splits as for ducted

The Victorian Energy Upgrades program, on a page updated in September 2026, offers up to $2,520 to replace a ducted gas heater with a 10 kW ducted reverse-cycle system. It offers the same up to $2,520 to replace ducted gas with four split systems, one 8 kW and three 3 kW. A 10 kW multi-split system attracts up to $2,940. Larger ducted systems get more, up to $4,200 at 16 kW and $5,530 at 22.4 kW.

At Going Rate's prices, four of a typical split system ($2,950) cost less than one ducted system ($14,000), and an equal rebate on both leaves that gap unchanged. The amounts are indicative upfront discounts, and the final figure depends on the products and the installer.

Environment Victoria and Renew report that 44% of Victorian houses use ducted gas heating with no cooling. In older homes of that kind, they found, replacing ducted gas with three splits in the living room and two sleeping areas cuts the cost of heating and cooling by 46 to 67%.

When ducted air is still worth it

Ducted makes sense when every room needs conditioning, the house is large, or the owner wants no units on the walls. It also suits a home with existing ducts in good condition, where the ductwork is already paid for. In those houses, compare quotes on the details CSIRO found leaking. Ask for a ceiling return over a wall-cavity return, ducts rated R1.5 with sealed joints, zoning by room group, and a duct leakage test after installation.

Ducted units are harder to compare on efficiency. Energy Rating says the star label is required only for single-phase, non-ducted systems under 30 kW, and ducted units under 30 kW may carry it without having to. A buyer should ask each installer for the unit's rated efficiency in writing.

For most other houses, count the rooms the household uses each day. Price three or four of a typical split system ($2,950) and ceiling insulation ($3,500) against one ducted system ($14,000), and add the yearly running cost ($1,300) to the ducted side.

Common questions