Beat Humidity & Mould Without a Dehumidifier: The Lüften Method

The Mould Problem: When Dehumidifiers Are Out of Reach

If you're reading this, you're likely dealing with the miserable consequences of excess humidity: black mould creeping across walls, condensation streaming down windows, that distinctive musty smell that never quite goes away. You know a dehumidifier would solve the problem, but spending £150-300 upfront simply isn't an option right now.

I completely understand. When you're struggling to make ends meet, choosing between heating and eating, a dehumidifier feels like an impossible luxury - even though the mould is making your family ill and damaging your belongings.

But there's another way, and it costs absolutely nothing to start doing it today.

What is Lüften?

Lüften (pronounced "LOOF-ten") is a German word meaning "to air" or "to ventilate." In Germany, it's a cultural practice so ingrained that most people do it without thinking. The principle is beautifully simple:

Yes, you read that correctly: you're bringing in cold air to reduce humidity, even though that cold air might actually have high humidity outdoors. This seems counterintuitive, but the physics are absolutely sound.

The Science: Why Cold Air Becomes Dry Air

Understanding why lüften works requires grasping one critical concept: relative humidity is temperature-dependent.

The Real-World Example

Let me give you a concrete example using actual Portsmouth weather data. Yesterday evening (21st November 2025) at 8pm, the outdoor conditions in Portsmouth were approximately:

• Temperature: 2°C
• Relative Humidity: 85%

At first glance, 85% humidity sounds very wet - surely bringing that air inside would make things worse? But watch what happens when that same air is warmed to a comfortable 20°C indoors:

This is the magic of lüften. You're not changing the amount of moisture in the air - you're changing its capacity to hold moisture. Warm air can hold much more water vapour than cold air, so when you warm up cold air, its relative humidity plummets.

Where Does the Heat Come From?

This is particularly effective in UK homes with solid brick walls. Your walls, floors, furniture, and other hard surfaces have been absorbing heat all day (whether from your heating system or solar gain through windows). This thermal mass releases its stored heat to warm the incoming cold air.

If you perform lüften first thing in the morning, you can also benefit from solar gain as the sun warms your home naturally throughout the day.

How to Practice Lüften Effectively

The Basic Method

1. Choose Your Timing: First thing in the morning is ideal (before heating kicks in heavily) or after cooking/showering when humidity spikes. In winter, outdoor air is coldest and driest.
2. Open Wide: Don't just crack a window. Open windows fully on opposite sides of your home to create cross-ventilation. This is called "Stoßlüften" (shock ventilation).
3. Set a Timer: 10-15 minutes is typically sufficient. You want complete air exchange, not prolonged cooling of your walls and furniture.
4. Close Everything: After 10-15 minutes, close all windows completely. The fresh, dry air will warm up quickly from your home's thermal mass.
5. Monitor Results: Track your indoor humidity levels to confirm it's working (more on this below).

Frequency

How often you need to lüften depends on:

• How many people live in your home (humans breathe out moisture)
• Your cooking and bathing habits
• Whether you dry laundry indoors
• How well-insulated and airtight your home is

A typical household should aim for 2-3 lüften sessions per day: morning, after cooking, and evening.

Watch It in Action

I've created a detailed video showing how I use this technique to maintain under 40% humidity throughout my home without running a dehumidifier:

Measuring Success: Why You Need Humidity Monitors

You cannot manage what you cannot measure. To effectively use lüften, you need to know your starting humidity levels and track how they change. Guessing simply doesn't work.

I use SwitchBot Meter Plus sensors in every room of my house. These affordable devices (around £10-15 each) continuously monitor temperature and humidity, storing the data in an app so I can track patterns throughout the day.

Having sensors in each room reveals surprising patterns. You'll discover that humidity varies dramatically between rooms - your bathroom might be at 70% while your bedroom sits at 45%. This helps you target your lüften efforts where they're needed most.

The Trade-Off: Energy vs. Mould

I need to be honest about the downside of lüften: it does waste heating energy.

When you open windows and let warm air escape, you're throwing away the heat you've paid for. Your heating system will need to work harder to bring temperatures back up. In energy terms, this is inefficient.

However, consider the alternative:

• Mould damages your belongings permanently (ruined clothes, furniture, books)
• Black mould causes respiratory problems, particularly in children and vulnerable people
• Severe mould makes properties unliveable and can reduce property value
• NHS costs from mould-related illness far exceed heating costs
• Landlords may evict tenants for mould issues (often unfairly blaming the tenant)

That said, lüften is more energy-efficient than leaving windows on trickle vents all day, which continuously loses heat. Short, sharp ventilation sessions minimise heat loss while maximising moisture removal.

Advanced Tips for Maximum Effectiveness

Target Problem Areas First

Use your humidity monitors to identify the worst rooms. Kitchens and bathrooms typically spike highest. Focus your lüften efforts here immediately after moisture-generating activities.

Don't Lüften When It's Raining

While outdoor cold air is generally dryer than warm indoor air, this breaks down during heavy rain when outdoor humidity approaches 100%. Check conditions before opening windows.

Adjust Heating Before Lüften

Turn radiators down or off 10 minutes before lüften to avoid heating outdoor air as it comes in. Turn heating back on immediately after closing windows.

Combine with Other Moisture-Reducing Strategies

• Use extractor fans when cooking and bathing (run for 15 minutes after)
• Dry laundry outdoors when possible, or in one room with the door closed
• Keep lids on pans when cooking
• Wipe down condensation on windows before it evaporates back into the air

When Lüften Isn't Enough

Lüften is excellent for managing normal household humidity, but it has limits. Consider saving for a dehumidifier if:

• You're already lüften 3-4 times daily and humidity stays above 60%
• Your home has structural damp issues (rising damp, penetrating damp)
• You live in a basement or ground-floor flat with chronic dampness
• Mould is growing faster than lüften can control it
• You have severe health conditions worsened by high humidity

If these apply, lüften can help manage the problem while you save up, but a mechanical dehumidifier will ultimately be necessary.

Final Thoughts: Free Doesn't Mean Ineffective

Lüften proves that expensive equipment isn't always necessary to solve problems. Sometimes the solution is simpler - and older - than modern gadgets suggest.

This German practice has kept homes mould-free for centuries. It works because it's based on physics, not marketing. Cold air holds less moisture. Warm that cold air up, and you've got dry air for free.

Yes, it takes discipline. You need to remember to open windows twice a day, even when it's freezing outside. You need to monitor humidity levels and adjust your routine accordingly. But the alternative - living with black mould creeping across your walls - is far worse.

If you're struggling financially, this is a genuine solution that costs nothing to start today. Pair it with £10-15 humidity monitors to track your progress, and you'll be amazed how effectively you can control indoor humidity without spending hundreds on a dehumidifier.

Your lungs, your belongings, and your family will thank you.