Airing, drying laundry and dehumidifiers the Spanish way

Key rules

• Daily airing: Open windows for 10 minutes a day, even in winter, ideally on opposite sides.
• Shutters: A shut window behind a closed shutter all day lets damp and mould build up.
• Laundry: Dry clothes outside or in a vented or condensing dryer before drying them indoors.
• Heaters: Never use butane, paraffin or brazier heaters in a closed bedroom.
• Dehumidifier: It reduces condensation but does not cure leaks or rising damp.

Air every day, even in winter

Open the windows for 10 minutes a day, ideally on opposite sides of the home so air moves through. Do it at a cooler time of day and switch the heating off while the windows are open.

Several short airings work better than leaving a window ajar all day. Run the extractor fan when you cook or shower, and keep the kitchen and bathroom doors shut while you do. Never block the ventilation openings in walls or windows.

Use persianas to help, not to seal

Persianas (roller shutters) block light and some heat, but they do not ventilate. A room with the shutter down and the window shut all day goes stagnant. Condensation and mould follow, especially in bedrooms.

A simple routine:

• Open shutters and windows for the daily airing.
• In winter, keep shutters partly open by day so the sun warms the room.
• Close them at night for some insulation.
• Look inside the cajón de persiana (the shutter box) for mould and gaps. Old ones often leak air and let cold in.

Dry laundry where the water can escape

A load of washing dried indoors can release about 1–2 litres of water into the air. Choose in this order:

1. A tendedero, the outdoor or ventilated balcony or patio line.
2. A vented or condensing dryer. A vented one needs its hose out of the window.
3. A small room with the door closed and the window open or the extractor on, ideally with a dehumidifier.

Spin clothes well first. Don't dry them on radiators in bedrooms or living rooms that are not ventilated.

Be careful with heaters

Butane and paraffin (queroseno) heaters have no flue. Burning butane gives roughly one litre of water per kilo, so they add damp. They also give off carbon monoxide, which can poison you in a poorly ventilated room. Don't use them in closed rooms, and never in a bedroom or while you sleep. Braseros (charcoal or wood braziers) are the most dangerous. Electric heaters make no combustion fumes. If you use a mobile butane heater, ventilate and fit a CO detector.

What a dehumidifier can and cannot do

A dehumidifier helps with condensation and high humidity from laundry, showers and cooking, mostly in closed rooms in winter. It can hold humidity around 40–60%.

It does not fix rising damp, leaks, damp coming through a facade or roof, or groundwater. The water keeps coming in. It also works badly with windows open.

Pick the type by room temperature. Compressor models work best in warmer rooms. Desiccant models suit cold rooms. Compressor units lose output below about 15°C.

As a rule of thumb for compressor models:

• A moderately damp room of about 20 m²: 8–10 litres a day.
• 30–50 m² with moderate damp: 12–16 litres a day.
• 50–80 m², or very damp spaces: 20–25 litres a day.
• A whole flat of 80–100 m² with constant condensation: 20 litres a day or more.

Go one size smaller for a slightly damp room. Go one size larger if you dry laundry inside without ventilation. Real rooms rarely match the test conditions on the box, so don't buy at the bare minimum.

The warnings and quick answers below cover heater safety, vented dryers and common damp questions.

What to watch out for

What to watch out for

• Indoor heaters without a flue can poison you: Butane and paraffin (queroseno) heaters have no flue. They give off carbon monoxide (CO), a gas you cannot see or smell, and it can poison you in a poorly ventilated room. Braseros, the charcoal or wood braziers, are the most dangerous and have caused many deaths. Never use these heaters in a closed room, in a bedroom or while you sleep. Choose an electric heater, which gives off no combustion fumes. If you do use a butane heater, ventilate the room, pick a model with an oxygen sensor and fit a CO detector.

• Butane and paraffin heaters add damp to the air: Burning butane releases roughly one litre of water per kilo burned. In a closed room this raises humidity and feeds mould. Switch to electric heating where you can. If not, open a window for a while after use.

• Drying laundry indoors fills the air with water: One load of washing dried indoors can release about 1–2 litres of water into the air. Clothes on radiators in bedrooms or living rooms without ventilation make this worse. Use a tendedero, the outdoor or balcony line, whenever you can.

• A vented dryer needs its hose outside: A vented dryer blows damp air into the room if its hose is not out of the window. Put the hose out of the window every time, or buy a condensing dryer, which collects the moisture in a tank.

Quick answers about damp, mould and dehumidifiers

Is black mould dangerous to my health?

Black mould in a damp home raises the risk of cough, wheeze, asthma and allergic reactions, but claims of poisoning from "toxic black mould" in ordinary homes are not well supported. Children, older people, people with asthma, allergies or lung disease, and people with weak immune systems are most affected. Serious infections mainly hit people with weak immune systems.

Can I just paint over damp stains?

No, painting over damp stains does not fix them, because the stains return and the paint blisters, peels or turns mouldy unless you stop the moisture first. Once the cause is fixed, clean and treat the mould, let the wall dry fully, then apply a stain-blocking primer and paint. Anti-mould paints only slow regrowth on occasionally damp surfaces and do not cure leaks, rising damp or constant condensation.

Is a dehumidifier worth buying, and what size do I need?

Yes, a dehumidifier is worth it for condensation and humidity from laundry, showers and cooking, but not for leaks, rising damp or water coming through walls or roofs. For a moderately damp room of about 20 m² choose roughly 8–10 litres a day, for 30–50 m² about 12–16 litres a day, and for 50–80 m² or very damp spaces 20–25 litres a day. Go one size up for rooms where you dry laundry, and in rooms below about 15°C choose a desiccant model, which copes better with cold.

Are ground-floor flats always damp?

No, ground-floor flats are not always damp, but the risk is higher. It depends on waterproofing, drainage outside, the age of the building, the state of pipes and gutters, and ventilation. Damp is more common in the humid north (Galicia, Asturias, Cantabria, the Basque Country), on the coast and in older buildings, so look for stains and a musty smell when you view.