Reverse cycle and Perth's weather
The summer load
Perth Metro's February mean maximum is 31.7 degrees, and the city sees 26 days above 35 in a typical year. Size the cooling side for those afternoons, not for an average day.
Winter mornings
The July mean minimum is 8.1 degrees, nights under 2 degrees come about four times a year, and below 0 only about once every five years. The ACT Government's example energy label shows heating capacity at 7 degrees and at 2 degrees outside, and a typical Perth July night sits nearer the 7 degree figure.
Your label zone
That same label's map groups Perth with Adelaide and Sydney in the average zone. Compare models on their average-zone stars: blue for cooling and red for heating, as Mitsubishi Electric explains the label.
How WA homes heat now
In 2006 the ABS found WA households with heating mostly relied on gas (46%), then reverse cycle (21%), wood (17%) and electric heaters (14%).
What reverse cycle can replace in a Perth home
| What you have now | Reverse cycle instead | |
|---|---|---|
| Evaporative cooling | Cools with windows open, and only cools (Seeley) | Cools with the house closed, and heats in winter |
| Gas wall heater | 85% efficient in the ACT Government's comparison | 370% to 600% in the same comparison |
| Electric heater | One unit of heat per unit of electricity (ACT Government) | 3 to 6 units of heat per unit of electricity |
| Wood heater | Wood to buy and store, and a flue to keep clean | No fuel to store, run from a remote |
Split, multi-split or ducted?
The ACT Government guide's rule of thumb is splits for homes under 180sqm or a few rooms, and ducted or multi-head for larger houses. With most Perth homes being separate houses, all three are on the table. Our Perth pages on split systems and ducted go into each, and the national reverse cycle page explains how the heat pump works.
Working out what it will use
Use the method rather than anyone's estimate. Take the unit's input power in kW (not its capacity), multiply by the hours you'll run it, then by your own electricity rate. The running cost tool does the sums.
If you're one of the roughly 36% of SWIS customers with rooftop solar, running the cooling while the panels produce makes the most of them, and our solar guide explains how to think about it. For settings, the federal Energy Rating calculator suggests 25 to 27 degrees in summer and 18 to 20 in winter.
Questions to ask before you buy
- What's the heating capacity at 7 degrees and at 2 degrees outside?
- How many stars does this model get in the average zone, for cooling and for heating?
- What's the input power at full output, so I can work out what it'll use?
- If it replaces a gas heater, who disconnects and caps the gas? That's a gasfitter's job.
- Is it sized for a 35-degree afternoon in my suburb, not just an average day?
What we'd do
If it were our Perth home
We'd judge reverse cycle on both its numbers: cooling capacity for a 35-degree afternoon, and heating capacity at 7 degrees for a typical July night. We'd compare models on their average-zone stars and have a reverse cycle specialist size it for the rooms we actually use. If an old gas heater was being retired at the same time, we'd have a licensed gasfitter cap it properly.
