Inverter vs Non-Inverter Aircon
A 1.5 HP inverter and a 1.5 HP non-inverter cool the same room. What differs is how they get there — and what it costs you.
Last updated · 7 min read
The first thing to settle: the HP rating means exactly the same thing on both. A 1.5 HP inverter and a 1.5 HP non-inverter both deliver around 12,000 BTU/hr of cooling and both suit the same size room. Sizing does not change. What changes is how the compressor gets there, and what that costs over a season.
How Each One Works
Non-inverter (fixed speed). The compressor has two states: full power, or off. It runs flat out until the room reaches the set temperature, shuts down, waits for the room to warm, then starts again. Temperature oscillates around the setpoint in a sawtooth.
Inverter. The compressor speed is variable. It runs hard to pull the room down initially, then throttles back to whatever output matches the heat entering the room — often 20–30% of maximum — and stays running continuously at that level.
The efficiency gain comes from two places. Running continuously at low speed is far more efficient than repeatedly starting at full speed, because compressor start-up draws a large current surge and wastes energy overcoming inertia. And matching output to demand avoids the overshoot of cooling harder than necessary.
Does the HP Rating Mean the Same Thing?
Yes, and this trips people up constantly. Horsepower on an air conditioner describes cooling capacity — roughly 9,000 BTU/hr per HP — regardless of the compressor technology behind it.
What differs is that an inverter's capacity is a maximum rather than a fixed output. A 1.5 HP inverter can modulate anywhere from roughly 0.4 HP up to 1.7 HP of effective cooling, often slightly exceeding its nominal rating during pull-down. A 1.5 HP non-inverter delivers 1.5 HP or nothing.
The practical consequence: do not downsize because you are buying an inverter. If the room needs 1.5 HP, buy 1.5 HP. An undersized inverter simply runs at maximum permanently, losing the entire efficiency advantage. Our aircon HP by room size calculator gives the requirement for either type.
How Much Do You Actually Save?
Published comparisons put the saving between 30% and 44% for equivalent capacity, with the higher end from studies of continuous operation in hot climates. One comparison of 18,000 BTU units found the inverter consuming roughly 3,471 kWh a year against 6,230 kWh for the fixed-speed unit.
| Usage pattern | Typical saving | Why |
|---|---|---|
| All day, every day | 35–44% | Maximum time at low modulated output |
| Evenings and nights | 25–35% | Good, but includes daily pull-down |
| A few hours occasionally | 10–20% | Mostly spent pulling the room down |
| Short bursts only | Minimal | Never reaches modulating operation |
That pattern matters more than the headline percentage. An inverter saves money by running gently for a long time. Switch it on for forty minutes a day and it spends that whole period at full output, behaving much like a fixed-speed unit while having cost more to buy.
Which Should You Buy?
Choose an inverter if the unit runs for long stretches — bedrooms overnight, offices through the day, anywhere in a hot climate. Long runtimes are where the saving compounds and where the price premium pays back, typically within two to four years of steady use.
A non-inverter can make sense if the room is used briefly and rarely, the budget is tight, or the supply is unstable — fixed-speed units have simpler electronics with fewer expensive parts to fail. Guest rooms and occasional-use spaces are the honest case for one.
| Inverter | Non-inverter | |
|---|---|---|
| Purchase price | Higher | Lower |
| Running cost | 30–44% lower | Baseline |
| Temperature stability | Steady | Oscillates |
| Noise | Quieter when modulating | Cycles on and off audibly |
| Repair complexity | More electronics | Simpler |
| Best for | Long daily runtimes | Occasional short use |
Two Things Worth Correcting
"Inverters cool faster." Only marginally. Both types run the compressor at full output during pull-down, so initial cooling speed is broadly similar. Some inverters briefly exceed nominal capacity, which helps slightly, but the difference is not what you are paying for.
"Leave an inverter running all day, it is cheaper than switching off." Partly true, and frequently overstated. Continuous low-level operation avoids repeated pull-downs, but leaving a unit running in an empty room still consumes electricity. The advice holds for gaps of an hour or two, not for a full working day.
Whichever type you choose, sizing matters more than technology. An oversized unit of either kind short-cycles and leaves the room cold and clammy — see our guide to aircon HP, BTU and room size, use BTU to HP to translate a spec sheet, and how to check your aircon's horsepower if you are matching an existing unit.
Frequently Asked Questions
Yes. The HP rating describes cooling capacity — about 12,000 BTU/hr in both cases — and both suit the same room. The difference is how the compressor delivers it.
Typically 30–44% for equivalent capacity, highest with continuous operation. Savings drop sharply with short runtimes, since the unit never reaches modulated operation.
No. Size for the room, not the technology. An undersized inverter runs at maximum permanently, losing the efficiency advantage and still failing to cool properly.
Only marginally. Both run at full output during pull-down. Some inverters briefly exceed nominal capacity, but speed is not the main benefit.
For gaps of an hour or two, often yes — repeated pull-downs are costly. For a full day in an empty room, no. The claim is frequently overstated.
Sometimes. They cost less up front and have simpler electronics, suiting rooms used briefly — guest bedrooms, for instance. For long daily runtimes an inverter is clearly better.
Typically two to four years with steady daily use, depending on rates and runtime. Occasional-use rooms may never recover the premium.