Air conditioning
in Carrum Downs
A 30 square metre living room in Carrum Downs needs about 4.08kW, against 3.11kW for the same room in Portland, because Carrum Downs peaks at 34.8°C where Portland hits 29.1°C. Installed prices here run $1,450–$3,700 for splits.
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Why Carrum Downs is different
Sizing advice written for "Melbourne" is written for an average that barely exists. Carrum Downs accumulates 46.1 cooling degree days a year and clears 35°C about 9.5 days. Portland, across Melbourne, accumulates 10.1 and clears 35°C about 2.5 days — roughly 5 times the cooling demand. That is why the same room needs a different size unit depending which suburb it sits in, and why a number quoted for the metro average will be wrong for most addresses in it.
What size you need in Carrum Downs
| Room | Approx size | Cooling needed | Unit to look for |
|---|---|---|---|
| Bedroom | 12m² | 1.63kW | 2kW |
| Large bedroom or study | 18m² | 2.45kW | 2.5kW |
| Small living area | 25m² | 3.4kW | 3.5kW |
| Living room | 30m² | 4.08kW | 4.2kW |
| Open-plan living and dining | 45m² | 6.12kW | 6kW |
| Large open plan | 60m² | 8.15kW | 8kW |
Sizing follows the design criterion AIRAH uses in its FairAir calculator: the 3pm outdoor temperature exceeded on no more than 10 days a year. We compute that figure for each suburb from Bureau of Meteorology daily records, then split the cooling load into a component that scales with how far the design temperature sits above 24C and a component from sun and internal heat that barely varies by location. That 50/50 split is our assumption, not AIRAH's. Treat the result as a starting point for a quote, not a substitute for an installer measuring your rooms.
What it costs to run here
Carrum Downs sits in the United Energy network area, where a residential flat rate currently runs about 27.35c per kilowatt hour (AGL Residential Standing Offer). On that rate, a typical 3.5kW split system used normally costs roughly $27 a year in cooling, against about $6 for the identical unit in Portland.
That figure starts from the appliance's registered energy rating data, then scales it by Carrum Downs's own cooling degree days against the reference site the rating uses (Richmond RAAF (067105), 113 degree days). Without that adjustment every suburb in the zone would show an identical number, which would tell you nothing.
On a time-of-use plan in this network, electricity between 15:00 to 21:00 costs about 38.37c against 22.99c off-peak. Cooling the house hard through that window is where summer bills actually get away from people. Pre-cooling before it starts costs noticeably less.
What changes a quote in Carrum Downs
Salt air shortens outdoor unit life here
Carrum Downs sits about 4.8km from the coast, and salt-laden air attacks aluminium fins and steel casings far faster than it does inland. Ask what corrosion protection the outdoor unit carries and read the coastal terms in the manufacturer warranty, because several brands reduce or exclude cover within a set distance of surf. That clause is worth checking before you choose the unit rather than after.
You probably need less than you think
Carrum Downs accumulates only 46.1 cooling degree days a year and clears 35°C about 9.5 days. Oversizing is the common and expensive mistake here: too much capacity short-cycles, dehumidifies poorly and costs more upfront and to run. If an installer quotes a size up without measuring the room, ask them to justify it.
Winter matters as much as summer
With 1320 heating degree days and July mornings averaging 6.4°C, a reverse-cycle system in Carrum Downs earns its keep for heating at least as much as cooling. Ask for the heating output at low ambient temperature rather than the nominal kW, because that figure is what determines whether it copes on the coldest mornings.
The peak window costs real money here
On a United Energy time-of-use plan, electricity runs about 38.37 cents during the peak window (15:00 to 21:00) against 22.99 cents off-peak, close to double. Cooling the house hard through that window is where summer bills get away from people in Carrum Downs. Pre-cooling before it starts costs noticeably less for the same comfort.
Installed prices
| System | Installed price | Suits |
|---|---|---|
| Small split (2.5kW) | $1,450–$2,300 | Bedrooms and studies |
| Large split (5-7kW) | $2,400–$3,700 | Living areas |
| Ducted, whole home | $8,000–$16,000 | Houses with roof access |
Melbourne pricing. See the full Melbourne cost guide for a breakdown by job, or the Victoria rebate guide for discounts that come off these figures.
About Carrum Downs
Around 23,160 people live in Carrum Downs (estimated for 2025), across roughly 8,307 occupied dwellings. The housing mix is 0.4% apartments, 79% separate houses and 19.6% semi-detached or townhouses, which is what drives most of the practical differences in getting a system installed here.
Nearby suburbs
Climate, network tariffs and housing stock shift across a metro, so the sizing and running costs on these pages differ from Carrum Downs's.
Sources and data
- ABS Census 2021, dwelling structure and medians by postcode
- ABS Regional population 2024-25 (population estimate basis)
- Bureau of Meteorology, Climate Data Online
- Australian Building Codes Board climate zone map
- AIRAH FairAir cooling calculator (design condition methodology)
- Consumer Data Right energy plan data (network and tariffs)
- energyrating.gov.au product database (zoned energy rating data)
Based on Australian Bureau of Statistics data. Source: ABS, Census of Population and Housing 2021 and Regional population 2024-25, licensed under CC BY 4.0. Climate data: Bureau of Meteorology, licensed under CC BY 4.0. Climate zones: Australian Building Codes Board. Tariffs: Consumer Data Right energy plan data. Appliance energy data: energyrating.gov.au (E3 Program).
Population is an estimate derived from the 2021 Census count scaled by regional growth to 2025, not an official count. Climate figures come from MOORABBIN AIRPORT (086077). Nearest qualifying station (still reporting, 54.9 yr of record, 98% complete). MOORABBIN AIRPORT (086077) is 15.2 km away, 2.8 km from the open coast against the suburb's 4.8 km, at 12 m against the suburb's 34 m. Stations are ranked on distance plus penalties for differing coastal exposure, elevation, NCC climate zone, record length and marine (sand-spit or island) siting.