Air conditioning
in Bonnyrigg
A 30 square metre living room in Bonnyrigg needs about 4.36kW, against 3.15kW for the same room in Kiama, because Bonnyrigg peaks at 36.5°C where Kiama hits 29.3°C. Installed prices here run $1,350–$3,500 for splits.
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Why Bonnyrigg is different
Sizing advice written for "Sydney" is written for an average that barely exists. Bonnyrigg accumulates 98.6 cooling degree days a year and clears 35°C about 15.1 days. Kiama, across Sydney, accumulates 21.5 and clears 35°C about 1.8 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 Bonnyrigg
| Room | Approx size | Cooling needed | Unit to look for |
|---|---|---|---|
| Bedroom | 12m² | 1.75kW | 2kW |
| Large bedroom or study | 18m² | 2.62kW | 2.5kW |
| Small living area | 25m² | 3.64kW | 3.5kW |
| Living room | 30m² | 4.36kW | 4.2kW |
| Open-plan living and dining | 45m² | 6.55kW | 6kW |
| Large open plan | 60m² | 8.73kW | 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
Bonnyrigg sits in the Endeavour network area, where a residential flat rate currently runs about 30.66c per kilowatt hour (ENGIE NSW ENGIE Standing elec). On that rate, a typical 3.5kW split system used normally costs roughly $64 a year in cooling, against about $14 for the identical unit in Kiama.
That figure starts from the appliance's registered energy rating data, then scales it by Bonnyrigg'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 16:00 to 19:59 costs about 42.34c against 32.45c 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 Bonnyrigg
Sizing for 36.5°C, not for the average
Bonnyrigg reaches 36.5°C on its hottest days and clears 35°C about 15.1 days a year. Every system loses output as the outdoor temperature climbs, so a unit specified against the nominal rating will disappoint exactly when you need it. Ask what the unit actually delivers at 40°C rather than at its test conditions.
Ducted is genuinely viable here
82.6% of Bonnyrigg dwellings are separate houses, most with accessible roof space, which makes ducted a real option rather than a stretch. The check that matters is roof cavity height and insulation condition, and any installer can confirm both in a five-minute inspection before quoting.
Family-sized homes, zoned systems
Average household size in Bonnyrigg is 3.3 people, and with mostly detached housing that usually means bedrooms in use at different times to living areas. Zoning a ducted system, or splitting across multiple heads, tends to beat one large unit on running cost even where the upfront number is similar.
Installed prices
| System | Installed price | Suits |
|---|---|---|
| Small split (2.5kW) | $1,350–$2,000 | Bedrooms and studies |
| Large split (5-7kW) | $2,100–$3,500 | Living areas |
| Ducted, whole home | $6,500–$12,000 | Houses with roof access |
Sydney pricing. See the full Sydney cost guide for a breakdown by job, or the New South Wales rebate guide for discounts that come off these figures.
About Bonnyrigg
Around 9,860 people live in Bonnyrigg (estimated for 2025), across roughly 4,862 occupied dwellings. The housing mix is 4.2% apartments, 82.6% separate houses and 12.8% 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 Bonnyrigg'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 HORSLEY PARK EQUESTRIAN CENTRE AWS (067119). Nearest qualifying station (still reporting, 29.0 yr of record, 98% complete). HORSLEY PARK EQUESTRIAN CENTRE AWS (067119) is 5.6 km away, 35.2 km from the open coast against the suburb's 30.1 km, at 100 m against the suburb's 55 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.