Air Purifier vs Air Conditioner: Your AC Is Not Cleaning the Air

Lift the front panel of a split AC and you will find a plastic mesh with openings you can see through. It catches hair, lint, insects and coarse dust — anything that would otherwise coat the evaporator fins and wreck heat transfer. It is a coil protector.

PM2.5 particles are, by definition, under 2.5 microns. They pass through that mesh as if it were open air. There is no version of a standard AC filter that changes this, and washing it more often does not help.

Several brands now sell split ACs with an added filtration layer, sometimes described as PM2.5, HEPA-type or an ioniser stage. These are not nothing — there is genuinely more media in the airstream than in a bare mesh — but three things limit them.

First, the media is thin, because an AC's fan is designed for a low-resistance path and a real H13 filter would choke it. Second, the filtration only happens while the indoor unit's fan is running, and on a thermostat cycle that can be half the time. Third, almost no manufacturer publishes a CADR figure for these models, which is the number that would let you compare them with a purifier. Where independent figures exist, they typically land well below an entry-level standalone purifier.

• Close the room. A sealed room is what an AC wants anyway, and it is also the condition under which a purifier reaches its rated clean-air delivery instead of endlessly treating infiltrating outdoor air.
• Place the purifier away from the AC's airstream. Sitting it directly under the indoor unit means it samples cooled, already-circulating air rather than the room's stagnant corners.
• Run the purifier continuously on a low or auto setting rather than blasting it for an hour. Clean air is a steady-state achievement, not an event.
• Keep the AC filter clean anyway. A fouled coil costs you 10-20% in efficiency and is a mould risk in Indian humidity.
• In winter in North India, the AC is off and the air is at its worst. That is the season the purifier earns its price.