Independent reference

Air purifier terms, in plain English

Buying an air purifier means wading through jargon — CADR, HEPA, MERV-13, ACH, PM2.5. This is a jargon-free reference that explains what each term actually means, why it matters for the air you breathe, and how to use it to choose well. No brand spin — just the science, clearly.

Start with the essentials

What is CADR?

Clean-air delivery rate — the single most useful number on the box, and how to match it to your room.

HEPA vs MERV-13

Two ways to capture fine particles. What each does, and why airflow often matters more than filter grade.

Air changes per hour (ACH)

How many times a purifier can replace a room's air in an hour — and the number to aim for.

What is PM2.5?

The fine particles behind most health concerns — where they come from and how filtration removes them.

More definitions

What is HEPA? (H13/H14)

What true HEPA means and whether the higher grades matter at home.

What is a Corsi-Rosenthal box?

The high-airflow DIY design, how it works, and DIY vs pre-built.

Do air purifiers work?

What the evidence says they can and can't do — and what decides it.

Ionisers & ozone: safe?

How they differ from filters, and why ozone is a concern.

VOCs & activated carbon

Why particle filters can't remove smells and gases — and what does.

ACH vs CADR

The two numbers that matter, how they differ, and how they relate.

Activated carbon filter

How carbon removes gases and odours, and how much you need.

How does an air purifier work?

The stages air passes through, from fan to filters to clean air out.

What is a pre-filter?

The coarse first layer that protects the main filter and lasts longer.

What is the AQI?

The air quality index number and colour, and how to read it.

Air purifier vs dehumidifier

Particles vs moisture — which you need, and when it's both.

True HEPA vs "HEPA-type"

Why the qualifier matters, and how to avoid weaker filters.

UV-C air purifiers

Do they work, are they safe, and the ozone caveat.

What is an air purifier?

The plain-English definition — what it is, does, and isn't.

Negative ions explained

What they are, whether ionic purifiers clean air, and the caveats.

Sq ft ↔ m² sizing

Convert coverage areas — and why to check CADR instead.

HEPA vs carbon

Particles vs gases/odours — which filter you actually need.

What is an air quality monitor?

Measuring PM2.5, CO2 and VOCs — and why it pairs with a purifier.

Air purifier vs fan

A fan moves air; a purifier cleans it — and can even worsen allergies.

Air purifier vs humidifier

Removing particles vs adding moisture — different jobs entirely.

What is formaldehyde?

A common indoor VOC from furniture — why you need carbon, not HEPA.

What is NO₂?

The traffic and gas-cooking pollutant — why HEPA can't touch it.

What is radon?

The radioactive ground gas — and why a purifier won't fix it.

What is ozone?

The reactive gas behind "ozone" purifiers — and why to avoid it.

Air purifier vs air conditioner

Cleaning vs cooling — why AC won't filter, and why you may want both.

Ozone generator vs air purifier

Not the same thing — and why ozone isn't for occupied rooms.

Air purifier vs houseplants

Do plants clean air? Why the NASA study doesn't scale.

What is a MERV rating?

The 1–16 filter scale, and why MERV-13 is the sweet spot.

What is off-gassing?

That "new" smell — why it's VOCs and what removes it.

What is a smart air purifier?

Sensors, auto mode and apps — which features actually matter.

Washable & permanent filters

Any good? Where reusable filters make sense and where they don't.

What is TVOC?

The single "how gassy is my air" number — and how to lower it.

What is PM10?

Coarse dust and pollen — and how it differs from PM2.5.

ULPA vs HEPA

More capture, less airflow — why HEPA wins at home.

What is PCO?

Photocatalytic oxidation — the theory, limits and ozone caveat.

What is CFM (airflow)?

How much air it moves — and how that relates to CADR.

Sick building syndrome

Headaches and stuffiness tied to a building — and the air link.

Air purifier vs air scrubber

Everyday appliance vs heavy-duty site machine.

What are dust mites?

A top allergy trigger — and what a purifier can and can't do.

Guides: by need & season

Plain-English guides on what a purifier does for a specific problem — and where to go for a specialist recommendation.

For allergies

Pollen, dust mites, pet dander and mould spores — how filtration helps.

For pets

Dander and hair (particles) vs odours (need carbon) — what to look for.

For mould

Capturing spores — and why you must fix the moisture too.

For smoke

PM2.5 particles vs smoke odour — why you need both filter types.

Wildfire & bonfire smoke

Protecting indoor air during an outdoor smoke event.

Winter damp & mould

Why mould spikes in winter and the three levers that control it.

Do they help with dust?

How purifiers cut airborne dust and dust-mite debris — and what they can't do.

For a baby's nursery

Quiet, low-cost and ozone-free — what to look for in a small room.

Car air purifiers

Do the little ones work? What actually cleans a car's air.

How often to change filters

Lifespans for pre-filter, HEPA/MERV-13 and carbon — and the warning signs.

What size do I need?

Match CADR to your room for the right air-change rate — with a table.

Where to place it

The best position for airflow, and what to avoid.

Do they use much electricity?

Typical wattages and yearly cost — and why efficiency matters.

For asthma

How filtering triggers may help — with the medical caveats clear.

For hay fever

Cutting indoor pollen, and why the bedroom matters most.

For an office

Quiet, low-cost, right-sized — clean air, focus and fewer sick days.

For VOCs & new builds

Paint and off-gassing are gases — why you need carbon, not just HEPA.

For a flat or rental

Portable, plug-in, no installation or landlord permission needed.

For a garage or workshop

Dust vs fumes — strong filtration, a tough pre-filter and carbon.

Running one at night

Why the bedroom matters most, and how to keep it quiet.

Purifier vs opening a window

Filtration vs ventilation — and why you want both.

For a large/open-plan room

Why big spaces need high CADR — or two units.

For a whole house

Can one unit do it all? The realistic options.

For a conservatory

Heat, glass, garden pollen — what to look for.

For cigarette smoke

Particles vs tar/odour — what it can and can't do.

For the kitchen & cooking

Cooking PM2.5 and smells — filter plus carbon, with your hood.

Do they help with viruses?

Reducing airborne virus particles — as one layer, not a cure.

How to improve indoor air quality

The four levers — reduce, ventilate, filter, monitor — and how they fit.

Are air purifiers worth it?

When they're genuinely worth the money — and when they're not.

Are air purifiers safe?

Yes for filter units — the one thing to avoid is ozone.

How to clean an air purifier

A simple routine — and which filters you clean vs replace.

Do they dry out the air?

No — they filter particles, not moisture. The myth explained.

Best time to run it

Why continuous low-speed wins — and when to turn it up.

For a bathroom

Spores and odour vs damp — why ventilation comes first.

For a basement

Musty damp and spores — plus the radon it can't fix.

For a home gym

Dust, rubber off-gassing and sweat — sized for hard breathing.

For a care home

Vulnerable residents in shared air — infection and odour.

For a nail salon

Acetone and acrylic fumes plus filing dust — carbon and extraction.

For a bedroom

The best room for one — sizing, quiet running and placement.

For a living room

Sizing a big, busy, often open-plan space that gathers everything.

Do they help with smells?

Why HEPA can't, and how much carbon you actually need.

Do they cool a room?

No — the honest answer, and what actually cools.

Do they help with snoring?

The congestion link — and the sleep side-benefits.

Can you wash a HEPA filter?

Mostly no — which filters you clean vs replace, and why.

How long do they last?

5–10 years for the unit — filters are the consumable.

How loud are they?

Decibels explained, and why sizing up makes it quieter.

How many do I need?

One per used room — air doesn't travel between rooms.

Can they make you sick?

Filter units don't — the one type to avoid is ozone.

For wood smoke & log burners

Fine PM2.5 plus odour — HEPA and a big carbon stage.

For cannabis smoke

Particles plus a sticky smell — why carbon capacity is key.

For traffic pollution

Living near a busy road — PM2.5, NO₂ and window timing.

For COPD

Cutting irritant triggers — and the ozone-free rule.

For sinus & congestion

When allergens drive a blocked nose — and when they don't.

Why does mine smell?

Musty, burning or chemical — match the smell to the fix.

For a caravan/motorhome

Compact, low-wattage picks for a small sealed space.

For a hair salon

Bleach/dye fumes, aerosols and hair dust — carbon plus HEPA.

For a restaurant

Where extraction ends and dining-room filtration begins.

For a hotel/Airbnb

Fresh rooms, fewer odour complaints, happier reviews.

For a waiting room/clinic

Shared air, vulnerable people — HEPA by air changes.

For student halls

Plug-in, no permission — mould, smells and dust.

For vaping

Clears the cloud fast; carbon for the sweet smell.

For incense & candles

The overlooked PM2.5 source — and how to clear it.

For renovation dust

A finisher for fine building dust — with safety limits.

How to use one

Beginner setup in six steps — and the common mistakes.

Filter light won't reset?

Why it stays on and how to clear it after a change.

Weak airflow?

The quick checklist to get the air moving again.

The 30-second version: match a purifier's CADR to your room so it delivers about 4–6 air changes per hour; make sure the filter is at least MERV-13 or true HEPA so it captures PM2.5; and check the noise and running cost at the speed you'll actually use, because a purifier only cleans while it's switched on.