Open the product page of any air purifier and you meet a wall of abbreviations: HEPA H13, CADR, ACH, dB, VOC. The numbers sound precise, but they only help if you know what they measure. Here is a plain-language guide to the specs that matter, so you can compare models with confidence.
How an air purifier works
Almost every home air purifier follows the same basic design. A fan pulls room air through one or more filters and pushes the cleaned air back out. Everything depends on two things: how well the filters capture particles, and how much air the fan can move.
That is why the specs fall into two groups: filtration quality and airflow.
Filtration specs
HEPA, and what H13 and H14 mean
HEPA stands for High Efficiency Particulate Air. In Europe, the standard (EN 1822) grades filters:
● H13 captures at least 99.95 percent of the most penetrating particle size.
● H14 captures at least 99.995 percent.
In the US, a “True HEPA” filter must capture 99.97 percent of particles at 0.3 microns. Both figures describe the filter itself under test conditions, not the performance of the whole machine in your living room. If air leaks around the filter or the casing, results drop, which is why a well-sealed design matters.
Beware of “HEPA-type” or “HEPA-like” wording. It is not a standard and offers no guarantee.
Activated carbon
A HEPA filter catches particles such as dust, pollen, pet dander and smoke. It does not remove gases or smells. For cooking odours, cleaning products and volatile organic compounds (VOCs), you need an activated carbon layer. The more carbon, the longer it lasts, so a thin carbon sheet is not equivalent to a thick carbon bed.
Things to avoid
● Ozone generators. Some devices produce ozone on purpose. Ozone is a lung irritant, so choose a purifier that doesn’t emit it.
● Ionisers without filtration. These may leave particles on surfaces rather than removing them.
Airflow specs
CADR
CADR (Clean Air Delivery Rate) tells you how much filtered air the unit delivers per hour, usually measured separately for smoke, dust and pollen. A higher CADR means faster cleaning. It is one of the most useful numbers because it is measured under a standard test, which makes comparisons fairer.
Room size
Manufacturers state a recommended room area. Treat it as a guide, and size up if you have high ceilings, open-plan spaces or a lot of pollution. A purifier that is too small can run at full speed all day and still not keep up.
ACH, air changes per hour
ACH tells you how many times per hour the purifier can clean the entire volume of a room. For allergy sufferers, 4 to 5 air changes per hour is a commonly used target. To calculate it, multiply the CADR by 60 if it is given per minute, then divide by the volume of your room.
Putting the specs to work
When comparing models, build a short checklist:
1. Is the filter a certified H13 or H14 HEPA?
2. Is there a meaningful activated carbon layer for odours and VOCs?
3. Does the CADR suit the size of the room?
4. Is the noise level acceptable at the speed you will actually use?
5. What do replacement filters cost, and how often are they needed?
A good way to practise is to take a brand that publishes full spec sheets and run it through the list. R-Pur, for example, makes air purifiers and respiratory masks, so its product pages are a handy reference for checking each point against real figures.
Compare these across a few products rather than relying on a single headline number. If you are choosing for a bedroom, put noise first. For a kitchen or living room, look hard at CADR and carbon.
Practical specs
Noise level
Noise is given in decibels (dB), typically at the lowest and highest fan speeds. A bedroom unit should be comfortable on its lowest setting, so check that figure rather than the maximum.
Filter life and running costs
Filters wear out, and replacing them is the main ongoing cost. Look at how often they need changing, what they cost and whether you can buy them easily. A cheap purifier with expensive filters can cost more in the long run.
Energy use
Purifiers run for many hours a day, so power draw adds up. Look at the wattage, and see whether there is an auto or eco mode that slows the fan when the air is clean.
Sensors and smart features
Some models include an air quality sensor that adjusts the fan speed automatically, plus app control. They are convenient but not essential. A good sensor adds real value only if it responds to the pollutants you care about.
Placement tips
Where you put the purifier matters almost as much as which one you buy. Keep it a few centimetres clear of walls and furniture so air can flow in and out, and avoid corners. Run it with doors and windows closed for the best results, and keep it on rather than switching it on and off, because pollutants return quickly once it stops.
