Ventilate and heat the right way: keep your home mould-free

Every household produces moisture day after day — through showering, cooking, laundry and simply breathing. Depending on the size of the household, several litres of water pass into the indoor air every day. That is completely normal and no cause for concern — as long as the moisture regularly finds its way outside.

That is exactly what proper ventilating and heating is about. With a few simple routines that together take only minutes a day, you keep humidity in the healthy range, protect walls and furniture — and even save heating energy along the way.

Why mould forms in the first place

Mould needs two things: moisture and a cool surface. Warm air can hold a lot of water — when it cools down at a cold spot, such as an outside wall or a window reveal, it releases part of that water as condensation. If the spot stays damp, mould spores find ideal conditions there.

The moisture itself comes from perfectly ordinary sources:

• Showering and bathing: a single shower releases roughly half a litre to a litre of water into the air.
• Cooking: steam from pots and pans adds up to about half a litre to a litre over the day.
• Drying laundry indoors: one load releases one to three litres of water into the room air, depending on the amount.
• Sleeping and breathing: each person gives off around half a litre of moisture per night — without noticing.
• Houseplants and aquariums: smaller, but steady sources of moisture.

Burst ventilation instead of tilted windows — how to do it right

A permanently tilted window seems convenient, but it is the least effective way to ventilate: it exchanges hardly any air, yet strongly cools the wall around the window — and that is exactly where moisture then condenses. In winter it also wastes a lot of heating energy.

Short, vigorous burst ventilation works far better: open the window fully, turn the thermostat down while you do, then close the window and continue heating. Cross-ventilation is the most effective method — open windows or doors on opposite sides at the same time, and the draught exchanges the entire air volume within minutes. Two to four times a day is enough: after getting up, after showering or cooking, and before going to bed.

How long you should ventilate depends on the season — the bigger the temperature difference between inside and outside, the faster the air is exchanged:

• Winter: 3 to 5 minutes of burst ventilation is enough — with cross-ventilation often just 2 to 3 minutes. The walls do not cool down in that short time.
• Spring and autumn: 10 to 15 minutes, ideally with a cross-draught.
• Summer: 20 to 30 minutes — best early in the morning and late in the evening, when the air outside is cooler and drier than inside.

Heating: keep a base temperature instead of letting rooms go cold

A common misconception: switching the heating off completely during the day saves the most. In reality, walls and furniture cool down — and cold surfaces are exactly where moisture condenses. Reheating rooms that have gone cold also takes a lot of energy — the supposed savings are far smaller than expected.

The better approach: lower the temperature by two to three degrees when you are out or overnight, rather than switching the heating off entirely. No living space should stay below about 16 to 17 degrees for long — not even the rarely used guest room.

Door habits matter too: keep doors closed between rooms of different temperatures. If you “heat” the cool bedroom with warm living-room air through an open door, you mainly transport moisture there — and it condenses on the cool walls. Each room is best heated with its own radiator.

Room by room: the routines that matter most

Every room has its own moisture peaks. These routines catch them before they become a problem:

• Bathroom: after showering, squeegee the water off tiles and shower walls, then open the window wide — in windowless bathrooms, let the extractor run. Keep the bathroom door closed so the humid air does not drift into the rest of the home.
• Bedroom: pull back the duvet in the morning so the night's moisture can escape, and air the room straight away. If you prefer to sleep in a cool room, keep the door closed during the day.
• Kitchen: put lids on pots, use the extractor hood while cooking, and ventilate briefly afterwards — that way the steam never settles in your home in the first place.
• Laundry indoors: dry it in a heated room with the door closed if possible, and air that room an extra two to three times. A high spin speed on the washing machine noticeably shortens the drying time.

Furniture at a distance — and a hygrometer as an early-warning system

Behind large pieces of furniture on outside walls, the air stands still — the wall behind stays cool and damp. So move wardrobes, beds and sofas five to ten centimetres away from outside walls to let air circulate behind them. The same applies to large pictures and heavy curtains on cold walls.

A small helper takes the guesswork out of it: a hygrometer shows the relative humidity and costs just a few euros. The ideal range is 40 to 60 per cent. If the reading stays above that for long, it is a clear signal to ventilate more often — long before any stain becomes visible.

First signs? Reporting early pays off

Even with good routines, keep an eye out for early warning signs: small dark spots on window reveals, silicone joints or in room corners, yellowish-brown damp stains, a musty smell, wallpaper starting to peel, or condensation that regularly sits on the window panes in the morning.

As a tenant you are obliged to report such observations to the property manager — and that works in your favour: the earlier a cause is found, the smaller the intervention in your home. A spot reported early usually means a quick fix — not weeks of work.

At KF Properties this is straightforward: report what you have noticed, ideally with a photo, directly via our online portal — our caretaker service will take a look at the spot promptly. If you have questions, you can also reach us via the contact form or by phone. This article is general information, not legal advice.