Which size do I need?
Replacement filters are chosen by size and grade, not by brand, whenever your machine uses standard media. Getting the size right is the only fiddly part, and it is usually printed on the filter you already have. Start there.
| Your purifier / box | Filter size | Recommended |
|---|---|---|
| Luggable Ultra (5-Fan) & most 16×25 CR boxes | 16×25×1" | 3M Filtrete MERV-13 16×25 — £75/pair |
| Luggable XL (7-Fan) & 20×25 boxes | 20×25×1" | 3M Filtrete MERV-13 20×25 — £58/pair |
| Exhalaron personal / desktop purifier | 6" or 6.5" round | Exhalaron EPA H11 — £32 each |
If you’re not sure, read the dimensions printed on the edge of your current filter, or measure the slot. Standard imperial furnace-filter sizes (16×25, 20×25) are the whole point: you’re never tied to one supplier. Our filter sizes guide explains nominal-versus-actual measurements and how to round an odd figure to the nearest standard size.
What do filters actually cost per year?
A single pair of MERV-13 lasts most homes 6–12 months, so a realistic annual spend is one pair, £58–£75 — roughly £0.11–£0.20 a day for clean air. Compare that with proprietary “HEPA-type” cartridges at £40–£80 each, often needed two or three times a year: £80–£160 or more annually for the same job. The gap is the cost of proprietary lock-in, and it is why we keep pointing people towards standard sizes.
- MERV-13, MPR 1900 — captures around 90–93% of airborne particles: PM2.5, pollen, fine dust, smoke, pet dander, and many bacteria and virus-carrying droplets.
- Genuine 3M Filtrete media — not a generic offcut; consistent pleat density and electrostatic charge.
- No lock-in — standard sizes mean you can rebuy from us or anyone, indefinitely.
Genuine vs compatible — and grade
If you buy compatible filters for a proprietary machine, check the grade carefully: a stated MERV number or true HEPA (H13), never vague “HEPA-type” wording, and dimensions that match your slot so air can’t bypass the media. Cheaper isn’t a bargain if the filter under-performs or doesn’t seal. For what the ratings actually mean, see HEPA H13 explained and HEPA vs MERV-13.
Don’t forget odours are a separate job
A particle filter — HEPA or MERV — does nothing for cooking smells, smoke odour or VOCs. Those need activated carbon, which works alongside the particle filter and is replaced on its own, shorter schedule. If smells are a concern, budget for both.
Signs it’s time to replace
- It’s been 6–12 months since the last change.
- Airflow from the unit has visibly weakened.
- The media looks grey and loaded, or smells musty.
- You’ve just been through wildfire smoke, decorating dust or a house move.
For the full detail on timing — and why you shouldn’t try to wash a tired filter — see how often to replace an air-purifier filter.
Fitting and sealing matter as much as grade
A high-grade filter only performs if air is forced through it rather than around it. When you fit a replacement, check the frame sits square in the slot with no gaps at the edges, and that any clips or gaskets seat properly — even a small bypass gap lets unfiltered air slip past and drags down the whole machine’s effectiveness. This is one reason buying the correct size matters so much; a filter that is slightly too small leaves a permanent leak. If in doubt, our filter sizes guide covers measuring and nominal-versus-actual dimensions.