HVAC Filter Size Guide: Cabinet, Model & Pack Matching

Match a replacement filter by the system’s required part number and actual fit, including depth. A nominal size such as 20 × 25 × 4 inches is a size label; it is not a promise that every filter with that label fits the same cabinet.

Record these details first

1. Photograph the existing filter label and the air-cleaner cabinet model.
2. Record height, width and depth, keeping inches and millimetres clearly labelled.
3. Check the frame or rail design and any upgrade kit already fitted.
4. Use the system maker’s permitted filter specification before comparing ratings and pack quantities.

AprilAire: choose by cabinet model

For 210, 213 and 216 filters, the manufacturer lists older 2120/2200 cabinets with upgrade kit 1213. Confirm that requirement before buying. These replacement filters are not generic filters for every UK boiler, ventilation unit or air conditioner.

A real nominal-versus-actual example

AprilAire lists the 213 as nominal 20 × 25 × 4 inches but gives actual dimensions of 20.6 × 26.63 × 4 inches. That difference is why cabinet and part numbers matter more than a rounded dimension alone. AprilAire 213 dimensions.

Filtrete: compare the complete size and pack

Read the actual dimensions on the existing frame and the replacement specification. Do not calculate an assumed actual size by subtracting the same amount from every nominal filter. Filtrete size selection guidance.

What does the rating tell you?

A filtration rating does not identify the shape or connection. Check the equipment specification before changing to a different rating. Pack quantity is a separate purchasing decision: compare the current total price and how many matching filters you need.

Manufacturer references

AprilAire 110, AprilAire 210, AprilAire 213, AprilAire 216, AprilAire 310, Filtrete MPR 1000. Checked 17 September 2026.

Browse HVAC products or use the UK compatibility checklist.