The RenAir size guide
How to find your return-air filter size.
Start with what is printed on your existing filter or grille. A grille’s advertised size does not describe the outside dimensions of the replacement filter.
1. Identify the filter slot
The current RenAir range is for egg-crate grilles with a 10 mm filter slot. The slot is the space the frame fits into; it is not the depth of the pleated media. Do not substitute a 20 mm-slot filter simply because the nominal grille dimensions match.
2. Separate the two measurements
Nominal grille size
The size used to identify the grille, such as 600 × 450 mm. Start here when choosing a size from the catalogue.
Filter bottom-box size
The outside length and width of the bottom box. That is the larger, lower part of the stepped frame. For every size in this range, the listed bottom-box dimensions are 14 mm smaller than the nominal grille size in each direction. For RenAir #39 (nominal grille 600 × 450 mm), the filter size is 586 × 436 mm. Do not measure the smaller top box.
3. Compare with the product page
Each listing gives the nominal grille size, bottom-box filter dimensions, filter slot and matching grille codes. Check all of these rather than choosing by appearance alone. If an existing filter does not match the listed dimensions, send us the measurements before ordering.
Find a filter by Polyaire EC-HF grille code
4. Keep the number and slot together
For a repeat enquiry, keep a record such as "RenAir #39 / 10 mm slot". RenAir numbers start at #21. A number from 1 to 20 is not a RenAir 10 mm filter. Always check the slot size as well. Another brand's number on its own is not a confirmed match.
Measuring safely
Do not climb on furniture or reach an inaccessible grille. Follow the system manufacturer’s instructions for access and filter removal. Ask an air-conditioning technician if you cannot inspect the filter safely.