The sticker price is the cheap part of any air conditioner — electricity is where the real money goes. The good news: the maths is simple, and the levers for cutting the bill are all free or nearly so.
The formula
Running cost per hour = the unit's power input in kW × your electricity tariff. Power input (what it draws from the wall) is lower than cooling output — a 3.5 kW-cooling portable typically draws 1.2–1.5 kW. At a typical Australian tariff around 30–35 c/kWh, that's roughly 36–52 cents per hour at full output.
| Unit size (cooling) | Typical draw | Cost per hour* | 4 hrs/day for summer* |
|---|---|---|---|
| 2.0–2.6 kW (bedroom) | ~0.8–1.0 kW | ~25–35c | ~$90–$130 |
| 3.3–3.5 kW (medium room) | ~1.2–1.4 kW | ~36–49c | ~$130–$175 |
| 4.1–4.5 kW (living area) | ~1.5–1.8 kW | ~45–63c | ~$160–$225 |
*At 30–35 c/kWh over a 90-day summer; your tariff and habits will vary. Crucially, these are full-throttle figures — with a thermostat set sensibly, the compressor cycles off once the room reaches temperature, and real-world costs land 30–50% below the table.
How that compares
A pedestal or tower fan costs 1–3 cents per hour; an evaporative cooler 2–5 cents; a split system cooling the same single room, being more efficient, roughly 20–40% less than a portable. So the hierarchy is: fan first if moving air is enough, evaporative if your climate is dry, portable when you need true refrigerated cooling without installation, split system if you own the home and cool that room daily for years.
Eight ways to cut the bill
First, seal the window kit — an unsealed gap can add several degrees of load, and a cheap seal kit pays for itself in weeks. Second, set the thermostat to 24–25° rather than 21°; each degree lower costs roughly 10% more. Third, use auto mode so the compressor cycles instead of running flat-out. Fourth, pre-cool in the late afternoon rather than fighting the 6pm peak from a hot start. Fifth, block western sun with blinds or thermal curtains. Sixth, close the door to the cooled room. Seventh, keep the filter clean — a clogged filter makes the compressor work longer for the same result. Eighth, put the unit on an energy meter plug for a week; nothing focuses the mind like seeing the actual number.
The bottom line
A sensibly sized, well-sealed portable running on a thermostat costs most households $1–$2 on a hot day — a fair price for sleeping through a heatwave. Size it right with the choosing guide, and if you're weighing efficiency, prefer units with a higher EER (explained in our terms guide).