Ventilation
How often should ventilation be serviced?
“Once a year” is the short answer, and it is often wrong. What really sets the interval is your system and your surroundings, not the calendar.
Published on · 7 min read
It is the question we get most often, and the one that attracts the vaguest answers. “Once a year” circulates everywhere without anyone specifying what is meant: changing a filter, cleaning a heat exchanger and having airflow measured are three different jobs, on three different schedules.
Here is how we reason on site, and what actually makes those intervals move.
Three jobs, three schedules
Start by separating what happens often from what happens rarely. Conflating the two leads either to needlessly frequent servicing or to filters left in place for three years.
| Task | Typical interval | Who can do it |
|---|---|---|
| Visual filter check | Every 3 to 6 months | You |
| Filter replacement | 1 to 2 times a year depending on loading | You or a technician |
| Cleaning extract valves | Once a year | You or a technician |
| Cleaning the unit and heat exchanger | Once a year | Technician |
| Airflow measurement and re-balancing | Every 2 to 3 years, or after any change | Technician |
| Duct network cleaning | Based on camera inspection | Technician |
What shortens the intervals
Two homes with the same unit do not wear out filters at the same rate. The following factors sometimes halve a filter's life:
- An air intake facing a busy road or a junction
- A wooded setting, with a spring pollen peak
- Pets, particularly long-haired cats and dogs
- Building works in the home or the block, however brief, with valves left unsealed
- An open-plan kitchen, which sends grease into the extract network
- A system permanently running at high speed, often because it was never balanced
The ten-second test
There is a simple check anyone can do without tools: hold a sheet of thin paper against an extract valve in the kitchen or bathroom, with the ventilation running normally.
If the sheet holds by itself, extraction is doing its job. If it falls, something is wrong — saturated filter, fouled valve, blocked duct or a partially failed unit. This test does not replace a flow meter reading, but it catches outright failures, and it is free.
A test with limits
The special case of heat recovery
An MVHR system needs more attention than extract-only, for a structural reason: it blows air into your living spaces. A saturated supply filter does not just reduce airflow, it becomes a route for what it was meant to stop.
Add the heat exchanger, which loses efficiency as it gathers dust, and the condensate tray, whose drain blocks silently. On these units, a full annual service is not a nicety: it is what allows the system to deliver the efficiency it promises.
What if it has never been serviced?
That is very common, and not a problem in itself. What changes is the order of operations: you do not start with a routine service, you start with a measured survey.
In practice we record airflow as found, inspect the network with a camera, and then decide what is needed. Sometimes a full duct clean is unavoidable; sometimes a filter change and re-balancing restore everything. Measuring before deciding avoids paying for the wrong job.
Frequently asked questions
Can you skip a year of servicing?
Nothing breaks immediately. What happens is more insidious: airflow drops gradually, motor consumption rises, and moisture starts to build up in the least ventilated rooms. The real cost of a skipped service usually appears two or three years later, as much more expensive work.
Should the ventilation be switched off at night or in winter?
No. Mechanical ventilation is designed to run continuously, and it is at night, in closed bedrooms, that air renewal matters most. Turning it off in winter to save on heating means creating a damp problem to avoid a marginal expense.
Are generic filters as good as branded ones?
What matters is the filtration class and the exact dimensions, not the logo. A generic filter of the right class, correctly sized, does the same job. Too coarse a filter lets through what it should stop; too dense a filter makes the motor work harder and cuts airflow.