How to Improve Ventilation and Prevent Moisture in Your Flat

Ventilation is one of those things people only think about once something goes wrong — mold in the bathroom, condensation on the windows, stale air in the bedroom. In Warsaw flats, especially after old windows are replaced with new sealed units, poor ventilation is one of the most common causes of excess moisture. Here is what you can do about it.

Why Does Ventilation Stop Working?

Gravity ventilation — through grilles in the walls or ceiling — works by pressure difference. Fresh air enters through gaps around windows and doors, while warm stale air exits through the ventilation duct. When old windows are replaced with new, airtight ones, the incoming airflow is cut off and the entire system stops functioning properly.

Ventilation grilles are also frequently painted over, clogged with dust, or — in older buildings — the ducts are simply blocked. The result: moisture stays in the flat and settles on the walls.

Simple Steps You Can Take Yourself

• Check the ventilation grilles. Hold a sheet of paper up to the grille — if it is not drawn toward the grille, the ventilation is not pulling. Clean the grille and check whether the duct is blocked.
• Ventilate regularly. At least 5–10 minutes in the morning and evening, especially after cooking and showering. A short, thorough airing is more effective than leaving a window slightly open all day.
• Use an extractor hood in the kitchen. One ducted to the outside, not a recirculation model with a carbon filter — a recirculation hood removes odours but not moisture.
• Do not dry laundry in the bedroom. Drying clothes release large amounts of steam — the best place is with an open window or in a room with mechanical ventilation.
• Keep furniture a few centimetres away from external walls. Air needs to circulate behind wardrobes — otherwise the corner becomes a dead zone with high humidity.

Window Trickle Vents — Simple and Effective

A trickle vent is a small component fitted into the window frame that allows a controlled amount of fresh air in without opening the window. It is the most cost-effective solution for flats where ventilation stopped working after the windows were replaced. Installation does not require any structural work — a handyman can fit them in about an hour.

If you want to find out whether trickle vents would solve the problem in your flat, send us a request through the contact form and we will assess the situation in person.

Mechanical Ventilation — When Is It Worth the Investment?

In a windowless bathroom or a kitchen with heavy cooking use, it is worth fitting a mechanical extractor fan connected to the ventilation duct. Modern models include a humidity sensor — they switch on automatically when humidity exceeds a set threshold. The cost depends on the model and the scope of installation — we confirm the details after assessing the existing setup.

Air Dehumidifiers — Temporary or Permanent Fix?

A dehumidifier can help reduce indoor humidity, but it does not address the root cause. If you are running it constantly and the moisture keeps returning, the source is elsewhere — a leak, thermal bridges, or absent ventilation. A dehumidifier is a useful supplementary tool, not a primary solution.

What Not to Do

• Do not block ventilation grilles — even if you feel a draught. Blocking ventilation is a direct route to mold.
• Do not leave the bathroom unventilated after a shower — leave the door ajar or switch on the extractor fan.
• Do not cook without the extractor hood on — 20 minutes of cooking can release tens of grams of steam into the air.
• Do not ignore condensation on windows — if the glass is wet every morning, the ventilation is not keeping up.