Ventilation and energy saving: how to combine fresh air with lower costs

A healthy indoor climate is indispensable, but many people fear that ventilating will drive up their energy bill. It doesn't have to. With the right approach, you get fresh air and keep costs low. In Flanders, where we have increasingly strict insulation standards, a thoughtful ventilation strategy is more important than ever. Read here exactly how it works.

Why is ventilation important?

Ventilation removes polluted air - think CO2, moisture, particulate matter, and chemicals from furniture - and brings in fresh oxygen. Without ventilation, moisture accumulates, leading to mold and health problems. A well-ventilated home is not only more comfortable but also healthier. Problems like allergies, headaches, and loss of concentration due to too much CO2 can be easily prevented.

Many people close the vents in winter to combat drafts and energy loss. That often creates more problems than it solves. Fortunately, there are systems that ventilate energy-efficiently without compromising comfort.

The different ventilation systems at a glance

In Flanders, we distinguish four basic types, indicated by letters A through D. Each type has a different effect on your energy consumption.

• System A (natural supply and exhaust): Air enters through vents and leaves the house via vertical ducts. Energy-efficient in summer, but in winter a lot of heat escapes. You mainly see this system in older homes.
• System B (mechanical supply, natural exhaust): A fan blows filtered air inside; exhaust happens naturally. Rarely used in homes because it often causes drafts and does not recover heat.
• System C (natural supply, mechanical exhaust): Fresh air comes through vents, and a central fan extracts the air. By setting the extraction at a lower flow rate, you already save energy, but vents still let cold air through.
• System D (balanced ventilation with heat recovery): Both supply and exhaust are mechanical, with a heat exchanger that recovers up to 90% of the heat from the exhaust air. This is the most energy-efficient, ideal for well-insulated homes and new construction.

How to lose the least energy?

The biggest energy gain is achieved by recovering the heat that otherwise disappears through windows or vents. With system D, this happens automatically. But you can also save with system C by using self-regulating vents that close in strong wind, or with demand control that adjusts extraction based on humidity or CO2. Discover more about balanced ventilation.

Practical tips for energy-efficient ventilation

A few simple adjustments make a big difference, even without an expensive investment:

• Replace old vents with self-regulating ones: They close automatically in strong wind and prevent cold drafts.
• Choose demand control: Sensors continuously measure air quality; only when needed does the system work harder.
• Maintain regularly: Dirty filters and clogged ducts increase energy consumption. Read here how often you should maintain.
• Ventilate briefly and intensively: If you open windows, do so for a maximum of 10 to 15 minutes per day, preferably in the morning. This refreshes the air without cooling down walls and furniture.
• Keep interior doors ajar: For optimal air circulation, it is important that air can flow freely.

Common mistakes

Many people think that ventilating only costs energy. But humid air requires more energy to heat than dry air. So by ventilating, you actually make heating more efficient. Another misconception is that you should leave windows permanently ajar - that's actually wasteful and costs unnecessary heat. Controlled and brief, or via a mechanical system, is always smarter.

How to ventilate in winter?

In winter, the temptation is great to keep everything tightly shut. Yet ventilation is essential precisely then, because we spend more time indoors and heat more. In the morning or after showering, open windows on opposite sides for a quick air refresh: 10 to 15 minutes is sufficient. If you have mechanical ventilation, let it run day and night at a low flow rate, and only switch to a higher setting during cooking or showering. Discover our range for energy-efficient ventilation in winter.

How long should you ventilate per day?

A healthy indoor climate requires continuous basic ventilation, even when you're not home. This can be done with a mechanical system on the lowest setting. If you want to ventilate with windows, do so two to three times a day for about fifteen minutes. Longer than that is a waste of heat. Even better is the combination of continuous basic ventilation and short bursts of airing.

Can I ventilate without vents?

Yes, that is possible with a balanced ventilation system (system D). No vents in the facade are needed because both supply and exhaust are mechanical. There are also decentralized units with heat recovery for bedrooms that you can install without major renovations. Discover how to install a ventilation system without vents.