Your options, ranked by long-term cost
| Where | Best for | Watch out for |
|---|---|---|
| Standard-size MERV-13 (CleanAirKits) | Luggable / CR-box owners; lowest lifetime cost, no lock-in | uses standard 16×25 / 20×25 sizes, not proprietary shapes |
| Brand direct (Levoit, Philips, Dyson…) | guaranteed-correct proprietary cartridge | highest ongoing price; you're locked in |
| Amazon / marketplaces | convenience, third-party "compatibles" | variable grade; many generics test below their claimed rating |
How to avoid overpaying
- Buy by size, not brand, wherever your unit allows it — standard 16×25 and 20×25 MERV-13 is cheap and widely stocked.
- Rebuy in pairs and change once a year for most homes — that's ~£58–£75 a year, not £80–£160.
- Skip "subscriptions" unless they beat rebuy price; a standard-size filter you can order any time needs no lock-in plan.
- Check the grade: a real MERV rating or true-HEPA H13, not "HEPA-type".
The cheapest no-lock-in route
If you own (or are willing to switch to) a standard-size purifier, genuine 3M Filtrete MERV-13 in 16×25 and 20×25 is the lowest lifetime cost we know of in the UK: ships from Oxford, free delivery over £100, and 10% off with code STAROFFER.