MVHR filter change and valve cleaning: how to keep the air in your flat fresh

In many newer flats, especially in Minergie buildings, it runs day and night without you noticing: comfort ventilation (Komfortlüftung), known in the UK as mechanical ventilation with heat recovery, or MVHR. It brings in fresh air, removes damp and stale air from the bathroom and kitchen, and catches dust and pollen along the way. A regular MVHR filter change keeps it doing that job well.

Clogged filters and dusty valves creep up on you: the air feels stuffy, the unit gets louder, the bathroom mirror stays steamed up for longer. Midwinter, when the system is working hardest, is a good time for a check. Here is how to go about it – and what to agree with property management first if you rent.

Why filters and valves need looking after

A comfort ventilation system blows filtered outdoor air into the living room and bedrooms and draws air out of the bathroom, WC and kitchen. Minergie Switzerland sums it up: comfort ventilation supplies fresh air, removes moisture and protects against mould, and its filters hold back pollen and dust.

Over time the filters clog up. The unit has to work harder, moves less air and often gets noisier. Dust also collects on the valves, and near the kitchen a thin film of grease as well. The result: less fresh air, rooms that stay damp for longer and grey rings on the ceiling around the valves.

1. Agree responsibilities with property management

Before you open anything, find out who is responsible for the system. There are two typical set-ups:

• A unit of your own in the flat, often in the storage cupboard, a bathroom cabinet or the hallway ceiling: tenants often change the filters themselves – but only if that has been agreed.
• A central system for the whole building: the filters are in the plant room. The caretaker or a maintenance company is responsible, and you simply report anything unusual.

According to Minergie, changing the filters is easy to do yourself after a short introduction, or it is done by the caretaker or installer. Ask property management who supplies and pays for replacements, whether the cost is included in the service charges and whether there are instructions. If in doubt, ask once rather than fit the wrong ones.

2. MVHR filter change step by step

Follow the unit's manual. The routine is usually similar:

1. Switch off the unit or put it into change mode as described in the manual.
2. Open the cover of the compartment, usually held by clips or screws.
3. Pull out the old filters and note which way round they sit – an arrow on the frame shows the airflow.
4. Wipe the compartment with a damp cloth and vacuum up loose dust.
5. Insert the new ones the same way round, close the cover and switch the unit back on.
6. Reset the change indicator as the manual describes and note the date.

The supply-air and extract-air filters are often different, with the supply side usually finer. Buy exactly the type printed on the old frame or given in the manual.

3. Clean the supply and extract valves

The round disc valves on the ceiling or wall can usually be removed by twisting or pulling. Important: their opening was set precisely when the system was commissioned so that each room gets the right amount of air.

• Mark the position: before removing a valve, draw a pencil line across the valve and the ceiling.
• Don't turn the centre disc: the setting must not change.
• Wash: with warm water and a little washing-up liquid; if there is grease from the kitchen, soak briefly. Not in the dishwasher unless the manufacturer allows it.
• Dry and refit in the same place: never swap valves between rooms.

The valves are often on the ceiling. For cleaning at height, the Swiss Council for Accident Prevention (BFU) recommends a stable stepladder with a safety bar rather than chairs or boxes.

4. Airing properly despite the ventilation

Comfort ventilation largely replaces opening windows, but it doesn't forbid it. According to Minergie you may open windows – preferably wide and briefly rather than leaving them permanently tilted. The Federal Office of Public Health recommends opening windows fully, cross-ventilating where possible and airing for at least five minutes in the heating season.

In winter the system brings dry outdoor air into the flat. If the air feels very dry, see our guide to dry air in your apartment in winter. Don't switch the ventilation to zero for good, though, unless the unit is designed for it and property management agrees – otherwise humidity rises in the bathroom and bedroom.

5. Plan professional maintenance

Not everything is a DIY job. Minergie recommends having the system checked by a professional every three to five years and the supply and extract ducts inspected about every six years, and cleaned if dirty. As a tenant you don't arrange this yourself; instead, tell property management if:

• the unit makes unusual noises or shows error messages;
• hardly any air comes out of the valves despite new filters;
• the valves smell musty or condensation drips from them.

The recirculating cooker hood in the kitchen is a separate job – our guide on how to clean extractor hood filters explains it.

The most common mistakes with comfort ventilation

• Vacuuming or washing the filters: they are designed for single use.
• Turning or swapping valves: the airflow is no longer balanced afterwards.
• Switching the system off "to save electricity": air exchange stops and humidity rises.
• The wrong type: too coarse lets pollen through, too dense slows the air down.
• Not reporting problems: a faulty system in a rented flat is a job for property management, not for DIY.

Priority Clean editorial teamOur cleaning team from Alberswil, Canton of Lucerne, shares hands-on experience from move-out, house, office and window cleaning across Central and Northwestern Switzerland.