The filter bill nobody puts on the box: what to check before you buy an air purifier

This is a research-based write-up. We read Coway's German site (coway.de) and its deal listing on 26 October 2026, and German retailer listings for filters. We have not tested a Coway purifier. This is general information, not medical advice.

An air purifier is a fan that pushes your room's air through a filter. The purchase price is the number on the box. The number that decides whether you are happy in three years is the replacement filter, because a purifier with a dead filter is a quiet fan.

What a purifier does, and does not do#

A HEPA filter catches fine particles: dust, pollen, pet dander, some smoke particles. It does not remove gases or smells. For those you need an activated-carbon layer, and even then it is limited. It also does not replace opening a window. And if you are buying for a health condition, a doctor or pharmacist is the right first stop, not a product page.

The three specs that matter#

1. CADR (clean air delivery rate). This is how much filtered air the machine delivers, usually in cubic metres per hour. It is the single most useful number, because it tells you how fast a purifier cleans a room.

Here is the sum. Room volume is floor area times ceiling height. A 20 m² room with a 2.5 m ceiling is 50 m³. Divide the CADR by the room volume and you get air changes per hour. Many guides suggest around four to five air changes an hour for people sensitive to dust or pollen. For that room, four changes an hour needs a CADR of about 200 m³/h. A purifier with half of that will still help, but slowly.

2. The HEPA grade. A true H13 filter is rated to remove at least 99.95% of the most penetrating particles; H14 is higher. Phrases such as "HEPA-type" or "HEPA-like" are not the same claim, so look for the grade.

3. Noise at the speed you will use. A purifier that is too loud at night gets switched off. Look for a quiet sleep mode, and for the decibel figure at each speed, not just the lowest.

The running cost nobody leads with#

Filters are replaced on a schedule, commonly about once a year with regular use, depending on the model and how much you run it. Prices vary a lot. As an order of magnitude, one German retailer lists an H13 filter set for the Airmega Aim at €29.99 and a Max2Green set for the Airmega 400 and 400S at €99.99, each described as about a year of use. Those are retailer prices for specific models, not Coway's own, so check yours.

Here is why it matters. Suppose a purifier costs €190 and its yearly filter set costs €60 (an example, not a quote). Over five years you spend €190 + 5 × €60 = €490, and the box price is only about 39% of that. Always compare purifiers on purchase price plus five years of filters, not on purchase price alone.

Coway's German site advertises a filter subscription ("Spar-Abo", "save on every filter"). We could not see its price, delivery intervals or cancellation terms. Before you sign up, read our subscribe-and-save maths and check you can pause or cancel online.

What Coway Germany sells#

Coway's German shop lists six Airmega models at our check: the Airmega 100 Bundle, Mighty (black and white), 150, 350 and 450. It advertises free express shipping, a 30-day return right and a warranty of two years or more, with the conditions behind each on separate pages that we did not read. A 30-day return right is longer than the 14-day withdrawal period that EU law gives you for most online purchases, which is a real advantage for a product you want to hear running in your own room.

One sale price shows how the discounts work: the Airmega 100 Bundle at €189.99 against a regular price of €299.99, which is about 37% off. As always, compare that "regular" price with other sellers. Our guide to checking a sale price is real shows how.

Match the model to the room#

Coway's deals are grouped by room size, which is a good way to shop. Start with your room's volume and your target air changes, find the CADR you need, then pick the model. Do not start with the biggest discount.

The deals right now#

These are the offers on the Coway deal cards at our last check (the card titles are in German, because the store is German):

• 41% off selected air purifiers (no code)

• 25% off the collection for large rooms and 25% off the collection for medium rooms (no code)

• Autumn sale, up to 40% off

• 10% off replacement filters when you subscribe

• 5% off your first order, 10% off selected items with a code, and free shipping

"Selected" is doing real work in several of these, so check that the model you want is included. See every current offer on the Coway coupons page.

Who should skip it#

If your problem is cooking smells, cigarette smoke or chemical odours, a carbon-heavy purifier or better ventilation may serve you better than particle filtering alone. And if you know you will forget to change filters, a cheaper unit with easy-to-find filters is a better buy than a premium one you let decay.

Our take#

The best purifier is the one sized to your room and fed with a fresh filter. Coway's range and return right look sensible, but the pages we read left the filter prices and subscription terms to a later click. Find those before you buy, and you will know what you are really paying.

Disclosure: the deal buttons on this page use affiliate links, so we may earn a commission if you buy. It does not change what we write. Read our disclosure.