How to find the right ventilation filter size
Updated October 28, 2026 · 4 min read
You can identify a ventilation filter from the model plate, the reference on its frame or its exact dimensions. Here is what to copy, measure and enter when searching.
Use the model, reference or filter dimensions
To find the right ventilation filter size, use the exact model from the unit’s rating plate, the reference printed on the old filter frame, or measure the old filter in millimetres. Any one of these can give you a useful search term, so not knowing the model does not bring the job to a halt.
Start with the information that is easiest to read. A clear model name is usually the simplest route. If the plate is difficult to reach or the model is unclear, inspect the old filter for a printed reference. If that has faded or is missing, measure the filter’s width, height and thickness. No guesswork is needed, which is handy because ventilation units are rather unsympathetic to guesswork.
Read the rating plate on the ventilation unit
The rating plate carries the exact model name of your heat recovery ventilation (MVHR) unit. Copy that name as it appears rather than shortening it or relying on what someone called the unit when it was installed. Small differences in a model designation matter when you are looking for filters for a particular ventilation unit.
Take a clear photograph of the whole plate if you can. That gives you something to check while searching and avoids repeated trips back to the unit. If you do not know how to open or access the ventilation unit, follow the manufacturer’s instructions. The opening method is model-specific and is not something worth improvising.
If the model name is readable, use it as your first search. You can still compare the listed dimensions with the old filter measurements before choosing. The plate identifies the unit; the old filter provides a second, physical check.
Check the old filter frame for a reference
Before reaching for a ruler, look around the frame of the old filter. A reference may be printed directly on it, and you can enter that reference into the search bar. Copy every letter, number and separator that remains legible. You do not need to work out what the code means.
Photograph the printed side before disposing of the filter. Dust and handling do not make faint printing any easier to read, and a photo lets you enlarge the detail on a screen. If there are two filters in the unit, inspect both frames rather than assuming that the information on one settles the matter for the other.
A printed reference is useful when the unit’s rating plate cannot be read. If the code is incomplete, move on to the dimensions instead of filling in the missing characters from memory.
Measure width, height and thickness in millimetres
Measure the old filter itself and record all three dimensions in millimetres. You need the width, the height and the thickness. The thickness is just as important as the other two measurements, even though it is the one people most often leave out when writing the size down.
- Remove the old filter using the procedure given in the manufacturer’s instructions for your ventilation unit.
- Measure one face of the filter from edge to edge and record the result in millimetres.
- Measure the other side of that face and record the second figure.
- Measure the thickness of the filter frame and add it as the third figure.
- Write the complete size in a form such as 200x415x48, keeping all three measurements together.
Search using the complete filter dimensions
When searching by size, enter all three measurements. Width and height can be swapped for the search, so a filter recorded one way does not disappear simply because you turned it through a quarter turn. Thickness still needs to be included. A search containing only the two largest dimensions leaves out part of the filter size.
On VMCDirect, you can find filters by ventilation unit model, by the reference printed on the old frame, or by dimensions such as 200x415x48 in the search bar. Measure to the nearest millimetre rather than rounding the figures into a size that merely looks close.
Keep the model name, frame reference and dimensions together if you have all three. They are separate ways to search, but they also help you check that you have read and measured the old filter carefully.
Identify every filter in the unit
A heat recovery ventilation (MVHR) unit has at least two filters: one on the fresh supply air entering the home and one on the extract air leaving it. Check each filter rather than removing one, measuring it and assuming the job is finished. Record the details from each frame clearly so they do not become mixed up.
If your searches produce no suitable result, write to VMCDirect with a clear photograph of the ventilation unit’s rating plate and another of the old filter. Include the dimensions you measured in millimetres. Those images provide the model information and the physical filter details without asking you to identify anything from memory.
Keep your notes or photographs after the search. The next time you need to identify the filters, you will already have the model, reference and dimensions to hand, rather than opening the unit simply to read them again.
Frequently asked questions
Can I find a ventilation filter using only its dimensions?
Yes. Measure the old filter’s width, height and thickness in millimetres, then search using all three figures, for example 200x415x48.
Does the order of width and height matter when searching?
No. The order of width and height does not matter for the search, but the thickness must still be included.
What if the reference on the filter frame is unreadable?
Use the exact model from the ventilation unit’s rating plate or measure the old filter to the nearest millimetre. A photograph may also help you inspect faint printing more closely.
What should I send if I cannot find a matching filter?
Send VMCDirect a photograph of the unit’s rating plate and a photograph of the old filter. Add the measured width, height and thickness in millimetres.