It’s a simple question with a surprisingly complex answer: can we ventilate our homes naturally, just by opening windows? In theory, yes. In practice, especially in modern, well-insulated homes, it’s a lot trickier than it sounds.
At Fibres Academy, we often hear from people trying to create healthier, more energy-efficient homes who are unsure about ventilation. So let’s break it down.
If you’d rather hear Andy and Chris talk through the ideas in this article, you can watch Episode 6 of Can I Just Ask? below. 👇
Why Fresh Air Matters
The air inside our homes can quickly become stale. Moisture from showers, cooking, and even breathing builds up, along with pollutants like carbon dioxide and volatile organic compounds (VOCs). Left unchecked, this can affect your comfort, your concentration, and even your health.
Ventilation is the process of getting that old, used-up air out and bringing fresh air in. The challenge is how to do it effectively, especially in homes that are well-sealed to save energy.
The Trouble with Natural Ventilation
Opening windows sounds easy enough. But doing it consistently, in all weather, without wasting energy, is harder than it looks.
One of our team members lives in a home without a mechanical system and takes air quality seriously. Despite using CO2 monitors and paying close attention to humidity, they still find it difficult to stay on top of things. Overnight, for example, carbon dioxide levels in the bedroom can rise above 1400 ppm—enough to make you feel groggy in the morning. The only solution? Getting up in the night to open windows.
Even during the day, natural ventilation depends on the weather. If it’s too cold, too still, or too humid outside, opening windows might not help much—or might make things worse.
Enter MVHR: Mechanical Ventilation with Heat Recovery
This is where MVHR systems come in. These systems quietly bring in fresh air from outside, filter it, and distribute it throughout the home, while also removing stale air from kitchens, bathrooms and other rooms. As a bonus, they recover heat from the outgoing air to help keep your home warm without wasting energy.
In practice, this means:
- No need to remember to open windows
- No cooking or bathroom smells lingering
- Reduced mould risk, even when drying clothes indoors
- Better overall air quality, all year round
Even in clean-air areas like Devon, MVHR filters reveal just how much dust, pollen and mould spores are in the air we breathe. Filtering these out before they enter your home makes a noticeable difference.
But Isn’t ‘Natural’ Better?
It’s a fair question. Natural sounds appealing. But when it comes to ventilation, natural often just means uncontrolled. You might get some airflow through trickle vents or window gaps, but it’s not reliable—and it’s often not enough.
Passive ventilation systems do exist and can work well in specific building designs, but they still depend heavily on external conditions like wind and temperature. For most homes, especially retrofits or standard layouts, they’re not enough on their own.
So What’s the Best Option?
If you live in a traditional, older house with plenty of natural air leakage, you might get by with window ventilation. But in a modern, airtight home, MVHR is increasingly seen as the gold standard. It takes the pressure off you to manage your air quality and quietly does the job in the background.
Think of it as letting the building do the hard work for you—so you can focus on living well inside it.