Dry Air from Central Heating: What Actually Helps (and What Doesn't)

Why the air gets so dry in winter

Heated air isn’t “dry” in itself. The culprit is cold outdoor air. In frosty weather, air can barely hold any water. When it comes in through a window and is warmed to 21 °C, its relative humidity plummets. Outdoor air at 80 % humidity can end up at just 20–30 % indoors once it’s warmed.

The warmer you heat your home and the more cold air keeps flowing in, for example through a permanently tilted window, the drier it gets. That’s why draughty, well-heated older flats often suffer more than modern, airtight homes.

Typical signs: a scratchy throat in the morning, dry or burning eyes, chapped lips, dry skin, static shocks from door handles and plants with brown leaf tips. Wooden floors and furniture can also develop small gaps and cracks.

Step 1: Measure, don’t guess

Air that feels dry isn’t always dry. A scratchy throat can also come from a cold or dust. So start with a hygrometer: not next to the radiator or window, but at chest height in the middle of the room. Watch the readings for a few days, morning and evening.

• Below 35 %: too dry, worth tackling.
• 35–40 %: borderline. Changing habits is often enough.
• 40–60 %: fine. No device needed.
• Above 60 %: rather too humid. Ventilate more instead. See our article on condensation on windows.

Step 2: Adjust ventilation and heating

Try these before buying a humidifier. They cost nothing and often solve the problem:

1. Don’t leave windows tilted. In winter, open them wide 3–4 times a day for 5 minutes. You get fresh air without a constant stream of very dry cold air.
2. Turn the thermostat down. Every degree lower raises relative humidity a little and saves on heating bills too. 20 °C in the living room and 17–18 °C in the bedroom suit most people.
3. Use moisture sources: if the rest of the home is very dry, leave the bathroom door open for a moment after showering rather than airing straight outside. Cook without a lid now and then. Only do this while the hygrometer reads low.
4. Add plants. Larger plants such as umbrella papyrus or snake plants release moisture and look good too.

Step 3: Choosing a humidifier

If humidity still stays below 35 %, a device can make sense. There are three types:

Evaporative humidifiers draw in room air and blow it through a wet wick. The air only takes up as much water as it can hold, so the risk of over-humidifying is low and there’s no mist carrying minerals or germs. Downsides: they’re a bit louder and the wick needs regular cleaning or replacing.

Ultrasonic humidifiers turn water into a fine, cool mist. They’re very quiet and economical. But whatever is in the water ends up in the air: limescale settles as white dust on furniture, and germs from a dirty tank can be inhaled. Fresh water every day is a must, and distilled water is best if your tap water is hard.

Steam humidifiers boil water and release germ-free steam. They’re hygienic but use much more electricity, and the hot steam is a scald risk in homes with small children or pets.

For most homes an evaporative humidifier is the least fuss. If you want something very quiet for the bedroom and will keep up with cleaning, an ultrasonic model works well.

Using a humidifier properly

• Pick the right size: check the manufacturer’s room-size rating. A small unit in a large open-plan space won’t do much.
• Use the humidistat: many units switch off at a set level. Set it to 45–50 %, not higher.
• Keep your distance: don’t place it right next to walls, curtains or wooden furniture, where moisture can collect.
• Fresh water daily: tip out what’s left, rinse the tank, refill. Standing water is the main cause of germs.
• Clean and descale weekly as described in the manual, usually with diluted citric acid or vinegar.
• Keep ventilating: a humidifier doesn’t replace fresh air.

When to be careful

In poorly insulated older homes with cold external walls, even 55 % humidity can cause condensation in corners and behind wardrobes. After a few weeks of humidifying, check window frames, room corners and the backs of furniture against external walls. If you see damp or dark patches, lower the target level.

Read next

• How to ventilate and heat in winter
• Cold home: stay warm and save on heating