The most common mistake people make with MVHR filters is ordering the wrong one — usually because two filters look almost identical but fit different units, or because the same unit changed its filter part way through production. This guide shows you how to identify the correct replacement first time, starting with the most reliable method and working down.
Start with the genuine part number
If you can find it, the manufacturer's part number is the single most reliable way to order. It specifies the exact filter — grade, size and type — so there is nothing to get wrong. Look for it:
- printed on the cardboard frame of your current filter;
- on a sticker or data plate on the unit itself;
- in the unit's installation or user manual, usually in a spares or maintenance section.
Search that number on our site, or send it to us, and you are done.
No part number? Identify your unit
If the old filter is unmarked, the next best route is your exact unit model. The data plate is usually on the side or underside of the unit and gives the model and often a serial number. Note the full model — not just “Systemair” or “SAVE”, but SAVE VTR 300, VSR 400, Topvex FC15 and so on — because each takes a specific filter.
Order supply and extract together
Most MVHR units use two different filters: a finer supply filter and a coarser extract filter. Manufacturers usually sell them as a kit with one of each, which is the simplest way to buy and means both get changed at the same time, as they should be. Some ranges also sell the supply and extract filters individually if you only need one. If you are unsure which you have, a standard kit is the safe default. For what the grades actually mean, see MVHR Filter Grades Explained.
Three things that catch people out
- Production changes. Some units changed filter size during their life. The Systemair Topvex TR04, for example, uses a different supply filter before and after 10 May 2010 — check your unit's age if a listing mentions a date.
- Standard vs optional grade. Several units offer a standard kit and a higher-grade “optional” kit (for example an F8 supply for allergy or pollution). Match what you had, or deliberately upgrade the supply — don't downgrade it.
- Handing and variants. Left- and right-hand versions of a unit usually take the same filter, but check the model suffix if in doubt.
Measuring as a last resort
If you genuinely cannot identify the unit or part, measure the old filter — length, width and depth in millimetres — and note whether it is a flat panel or a bag (pocket) filter, plus the grade if it is printed. Send us those details and we will match it. Measuring alone is the least reliable method, because filters of the same size can be different grades, so treat it as a fallback.
Which brands we cover
We supply genuine replacement filters for the major UK ventilation brands, including Systemair (SAVE, Villavent, Topvex and Geniox), Vent-Axia and more — the real manufacturer parts, sourced from the same supply chain, at trade-friendly prices.
Find your filter
- MVHR & ventilation replacement filters
- Systemair Topvex filters
- Systemair Geniox filters
- Air curtain filters
Still not sure? Send us your unit model or a photo of the old filter's frame and we will confirm the right one before you order.
Related guides
- MVHR Filter Grades Explained: ISO 16890, G4, M5 and F7
- Ventilation System Maintenance: Best Practices for Healthy Air
- What Is MVHR? Pros & Cons Explained
Frequently asked questions
How do I know which filter my MVHR unit takes?
Use the genuine part number if you can find it (on the old filter frame, the unit's data plate, or the manual). Otherwise identify your exact unit model and order the matching filter or kit.
Do I need to replace both the supply and extract filters?
Yes — change both at the same time. They are usually sold together as a kit for exactly this reason.
Are all filters for my unit the same?
Not always. Some units changed filter size during production, and many offer a standard and a higher-grade option. Check the date and grade if the listing mentions them.
Can I send you a photo to check?
Yes. Send a photo of the old filter's frame (with any printed part number or dimensions) or your unit's data plate, and we will confirm the correct filter before you order.