Air Purifier vs Air Conditioner: What Each One Actually Does to Your Air

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Short answer: an air conditioner changes the temperature and humidity of the air in a room; an air purifier removes particles from it. A split system recirculates the room’s own air through a coarse filter that keeps dust out of the machine, and it does not bring in fresh air. A HEPA air purifier is built and rated to capture fine particles such as smoke, pollen and pet dander, but it does not cool, heat or dry the room. They do different jobs, so most Australian homes that care about both comfort and air quality run them together.

The difference in one table

What an air conditioner does to your air

A common belief is that an air conditioner brings fresh air in from outside. Daikin says the opposite: air conditioners “draw air from inside the room, and cools or heats it, and returns the air back into the room.” The outdoor unit exchanges heat, not air.

Three things happen to the air on its way through:

• Temperature. The coil cools or heats it. This is the job an air conditioner is built for.
• Humidity. Cooling pulls moisture out of the air, and many units have a Dry mode. Daikin describes Dry mode as eliminating humidity “while maintaining the indoor temperature as much as possible.”
• Coarse filtering. A washable filter in the indoor unit catches dust and lint before it reaches the coil. Daikin’s advice is to clean it every two weeks, more often in dusty homes, and says replacing a blocked filter with a clean one can cut energy use by 5% to 15%.

Some brands add an extra filter. Daikin says all its split systems have “an air-purifying filter”, that many models have a titanium air-purifying filter that traps “most microscopic airborne particles”, and that its split systems are approved under the National Asthma Council’s Sensitive Choice program. Those are real features, but we found no split system sold in Australia, including models marketed with purifying features, that publishes a clean air delivery rate, so you cannot size one as a purifier the way you can a HEPA unit. And like any central filter, it only cleans while the unit is running: the US EPA notes that HVAC filters “work to filter the air only when the system is operating.”

What an air purifier does

A portable air purifier pulls room air through a stack of filters and pushes it back out. In a HEPA unit the stack is usually a washable pre-filter for hair and lint, a carbon layer for some odours, and a HEPA filter for fine particles. It does nothing to the temperature or humidity.

The number that matters is the clean air delivery rate (CADR): how much particle-free air the unit delivers. You size a purifier by matching its smoke CADR to the floor area, so you can work out whether it will keep up with your room before you buy. Our best air purifier guide sizes every pick this way, and has a two-question finder if you want a quick answer.

Limits worth knowing, from the US EPA’s guide to air cleaners: “No air cleaner or filter will eliminate all of the air pollutants in your home”, most filters target either particles or gases, not both, and “Filtration does not replace the need to control pollutants and ventilate.” The EPA also says to avoid air cleaners that intentionally produce ozone.

Does an air conditioner purify the air?

Partly, and not in a way you can measure from the box. A split system’s standard filter is there to protect the machine and catch visible dust. Models with an added purifying filter do more, by the maker’s account, but without a CADR there is no way to compare one with a purifier or to know how quickly it clears a room after, say, smoke gets in.

Two practical consequences. First, keep the air conditioner’s filter clean whatever else you do: it is the cheapest air quality and efficiency win in the house. Second, if you need particles out of the air (smoke, pollen, dander, dust mite allergen), buy a HEPA purifier with a published CADR rather than relying on the air conditioner.

Running both together

Yes, you can run an air purifier with the air conditioner on, and the combination works well. Closing up the room to cool it also helps the purifier, because NSW Health notes a purifier must be used “in small, well-sealed areas” to work well. A few setup points:

1. Close doors and windows. The purifier then cleans one body of air instead of an endless supply from outside.
2. Size the purifier to the room. Use the smoke CADR and the floor area, not the room size printed on the box.
3. Do not block either machine. Leave space around the purifier’s intake and outlet, and avoid putting it where the split system’s airflow blasts straight into it.
4. Clean both pre-filters. The air conditioner’s every couple of weeks (Daikin’s advice), the purifier’s as its manual says.
5. Still ventilate. Air the room when the outdoor air is clean, or run an exhaust fan. Neither machine replaces fresh air.

Bushfire smoke: which air conditioners are safe to run

This is where the difference matters most. Victoria’s Better Health Channel advises: “Do not use air conditioners that draw in air from outside when it is smoky outside.” Its guidance by type:

Source: Better Health Channel, “Using air conditioners when it’s smoky outside”. Check your own unit’s manual for any fresh air setting.

NSW Health adds two points: switch the air conditioner to recirculate if it has the function, and “consider using an air purifier with a high efficiency particle air (HEPA) filter to remove smoke from your indoor air.” It also warns that humidifiers, negative ion generators and odour absorbers “do not remove fine particles in bushfire smoke.” For picks sized for smoke, see the bushfire smoke purifier guide.

Which one do you need?

Start from the problem, not the product:

My setup: the purifier in my bedroom

My bedroom is 12.5 m², and a Coway Airmega 150 runs beside the bed on Silent overnight. I chose it on two numbers. Coway US rates it at a smoke CADR of 153 cfm on the AHAM test, which by the US EPA’s sizing chart (about two-thirds of the floor area in square feet) covers about 21 m², so in my room it has spare capacity and can run quietly. And on Silent, the Decibel X app on my phone averaged 32.1 dBA at one metre. A phone app is not a certified sound meter, but it is a fair comparison point.

The clearest evidence of what it does is the pre-filter. After one month it was coated in grey dust and hair from my dog: material the purifier pulled out of my bedroom air. I have not logged particle counts, so I am not giving you a percentage. The point for this comparison is simple: that is a job for a purifier, and Coway rates the unit at 35 W, a small fraction of what any air conditioner draws.

Full detail in my Coway Airmega 150 review.

Purifiers that pair well with an air conditioner

Three HEPA units with published airflow figures, sized for the rooms Australians most often air-condition. Room sizes use the US EPA’s sizing chart (about two-thirds of the floor area in square feet), applied to the US smoke CADR at a standard 2.4 m ceiling.

Bedrooms~21 m²by the EPA rule

My pick | I own it

Coway Airmega 150

Smoke CADR 153 cfm (Coway US, AHAM test; Coway Australia lists 281 m³/h on the GB/T test) | 35 W | no ioniser listed (Coway) | Sensitive Choice approved | 32.1 dBA on Silent at 1 m (my reading) | $254, sold by Coway Australia (2 Nov 2026)

Check the Airmega 150 price on Amazon →

Living areas520 m³/hCADR, GB/T test (Philips)

Living rooms

Philips PureProtect 3200

HEPA NanoProtect + carbon | no ions or ozone emitted (Philips) | 36 W | CADR is on the Chinese GB/T test, not AHAM, so not directly comparable | $382, sold by Amazon AU (2 Nov 2026)

Check the Philips 3200 price on Amazon →

Large rooms~46 m²by the EPA rule

Open-plan and smoke

Coway Airmega 400

Smoke CADR 328 cfm (Coway US, AHAM test; Coway Australia lists 677 m³/h on the GB/T test) | two-sided intake | 66 W | Sensitive Choice approved | $849, sold by Coway Australia (2 Nov 2026)

Check the Airmega 400 price on Amazon →

Five more picks, including budget options, are compared in the best air purifier guide, and the HEPA claims behind them are checked in the best HEPA purifier guide.

Air conditioners with built-in purifiers, and purifier fans

Split systems with purifying filters. Worth having, and worth asking about when you replace a unit. Just treat the claim as a bonus, not as a substitute for a sized HEPA purifier, because we found no published CADR to check it against.

Ducted systems. If you have ducted air conditioning, ask your installer whether the return air filter can take a better grade. The US EPA suggests a MERV 13 filter, “or as high a rating as your system fan and filter slot can accommodate.” A denser filter can restrict airflow, so this is a question for the installer, not a swap to do blind.

Purifier fans. Products sold as a purifier and fan in one move air across you, which feels cooler, but they do not refrigerate the air, so they do not lower the room temperature the way an air conditioner does. Judge them as purifiers: look for a published CADR.

Ionisers and plasma features. Some purifiers and some air conditioners add ion generators. NSW Health says negative ion generators do not remove fine smoke particles, and the US EPA advises avoiding devices that intentionally produce ozone. If your unit has an ion or plasma setting, a HEPA filter does the real work; you can leave it off.

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Written by Jayce Love

Former Royal Australian Navy Clearance Diver and TAG-E counter-terrorism operator. Founded Clean and Native to apply the same rigorous thinking to the home environment.

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