Measure Zehnder ComfoD 350 filters before choosing a size
Updated October 28, 2026 · 5 min read
ComfoD filter sizes vary by model, and the 350, 450 and 550 appear in two formats. This guide shows what to measure, how to identify your set and how to replace both filters without guessing.
The filter size for each ComfoD model
Zehnder ComfoD 350 filters can be 198 × 500 × 14 mm or 500 × 197 × 16 mm, so measure the filters already in your unit before choosing a set. The same warning applies to the ComfoD 450 and 550. Other models in the ComfoD range have one size listed in our catalogue.
Every ComfoD unit covered here uses two filters. One filters the fresh air entering the home, known as the supply side, and the other sits on the extract side carrying stale air away. The two positions do different jobs, but both filter dimensions are the same for the model concerned.
- ComfoD 150: two filters measuring 150 × 237 × 24 mm
- ComfoD 200 and 250: two filters measuring 150 × 292 × 24 mm
- ComfoD 300: two filters measuring 198 × 500 × 14 mm
- ComfoD 350, 450 and 550: two filters measuring either 198 × 500 × 14 mm or 500 × 197 × 16 mm, depending on the unit version
Why the ComfoD 350, 450 and 550 must be measured
The model name alone does not settle the size for these three units. Our catalogue records two formats across the ComfoD 350, 450 and 550: 198 × 500 × 14 mm and 500 × 197 × 16 mm. This is not merely the same measurement written in another direction. The thickness changes from 14 to 16 mm, while the other face dimension changes from 198 to 197 mm.
Take the old filter out and measure it in millimetres as width × height × thickness. Measure the filter itself rather than estimating the opening by eye. A few millimetres may look unimportant while you are holding a dusty filter in a plant room, but the figures are what separate the two listed formats.
The ComfoD range is older than the ComfoAir Q range. Check the full model name on the unit’s rating plate and do not choose filters from the Zehnder brand name alone. Similar names are not enough to identify the dimensions.
Model numbers, references and dimensions all help
The exact model is normally printed on the ventilation unit’s rating plate. The old filter frame may also carry a reference. References encountered for the ComfoD 200 and 250 include 400100013 and 400100014. For the ComfoD 350, 450 and 550, references encountered include 400100085, 528006160, 528006180 and 006040220.
A printed reference is useful, but on a 350, 450 or 550 we would still measure the old filter because two sizes are listed for those models. If the printing has faded, the model plate and physical dimensions give you the other routes to identification.
On VMCDirect, you can find filters by model, by reference or by dimensions. The filters sold for these ventilation units carry the VMCDirect brand.
Replacing both filters without losing track of their positions
The cover and filter access arrangement can differ by unit version, so use the manufacturer’s instructions for opening and closing your particular ComfoD. The same applies if the unit’s supply and extract positions are not clearly marked. Do not assume that a particular side is always supply just because a picture online shows it that way.
- Read the full model name on the rating plate before removing the filters.
- Open the filter access as described in the manufacturer’s instructions.
- Before pulling anything out, note which filter sits in each position and the direction of any airflow arrow on its frame.
- Remove both filters. For a ComfoD 350, 450 or 550, measure the old filter in millimetres and check all three dimensions.
- Fit the new filters in the correct supply and extract positions. Align each airflow arrow with the direction shown by the unit or its instructions.
- Close the filter access following the manufacturer’s instructions.
- Reset the filter counter using the unit display, controller or application, depending on the model. The precise menu is given in the manufacturer’s instructions.
Airflow arrows and filter grades matter
An arrow on the filter frame indicates the airflow direction. A filter installed backwards may filter poorly and can deform, so copy the direction recorded before removal or follow the markings on the ventilation unit. If the old filter has no readable arrow, use the manufacturer’s instructions rather than guessing.
A common arrangement is a G4 coarse filter on the extract side to protect the heat exchanger, with an F7 fine filter on the supply side to retain pollen and fine particles from incoming air. Some installations use F7 filters on both sides, although these restrict airflow more. Keep each grade in its intended position instead of relying on left and right.
Do not wash or vacuum an F7 filter because this damages its filter material. A G4 can be vacuumed between replacements, but that does not replace fitting a new filter when required.
Resetting the warning completes the job
Many heat recovery ventilation (MVHR) units display a filter message according to a time counter, not because they have measured how dirty the filters are. That means the warning can appear before or after the filters actually need attention. Once the filters have been replaced, reset the counter so the next reminder starts from the new set.
Most manufacturers advise replacing ventilation filters about every six months and checking them in between. Conditions such as a busy road, building work, countryside pollen or pets can make more frequent attention necessary.
Leaving dirty filters in place can reduce airflow into the rooms. The ventilation unit may also become noisier as its fans work harder, use more electricity and allow dirt to reach the heat exchanger. Replacing the correct size and fitting it in the airflow direction avoids adding another problem while solving the first one.
Frequently asked questions
Do all Zehnder ComfoD 350 units use the same filters?
No. Two sizes are listed for the ComfoD 350: 198 × 500 × 14 mm and 500 × 197 × 16 mm. Measure the old filter before choosing.
How many filters does a ComfoD unit need?
The ComfoD models covered here use two filters: one on the incoming supply air and one on the outgoing extract air.
Can I clean and reuse an F7 filter?
Do not wash or vacuum an F7 filter because its filter material can be damaged. A G4 may be vacuumed between replacements, but this does not replace changing it.
Where do I reset the ComfoD filter warning?
Depending on the model, the counter is reset through the unit display, a controller or an application. Follow the manufacturer’s instructions for the exact menu.