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The ultimate ventilation guide for a healthy home

Good ventilation in your home is not a luxury; it’s a must. A reliable installation extracts dirty indoor air and systematically replaces it with fresh outdoor air. So you’re sure to have good quality indoor air whether you’re working, relaxing, or having a quick shower. Can’t see the wood for the trees in our extensive range? Don’t know which technical solutions are best suited to your day-to-day life? This ultimate ventilation guide will set you on the right tracks.


This guide summarises how ventilation can offer a solution to familiar problems: room by room at home. We look at the main challenges in detail and link them to efficient solutions, so you can discover more about the available systems and their specific advantages. After reading this guide, you can make an informed choice for a ventilation solution that deals the problems you’re facing at home.


The air quality inside many homes is much worse than it is outdoors. When you realise how much time we spend indoors on average (some 90%!), that definitely requires some attention. As well as causing numerous health problems, unhealthy air can also harm your home.

Dirty air in indoor spaces can cause tiredness, headaches and coughs, and is often caused by issues Such as mould in the home, unpleasant odours, and damp walls. So there’s no doubt that good ventilation is important for healthy and comfortable living. Think of it like this: you wouldn’t want to live in a sealed box where you soon struggle to breathe fresh air, would you?

Good ventilation prevents all kinds of problems with moisture in the home and the ailments they can cause. So it’s not just essential for the longevity and comfort of your home, but also for your health. Find out what problems a healthy indoor climate in your home can prevent.

Drowsiness, fatigue, loss of concentration…

Do you wake up in the mornings feeling like you haven’t had a good night’s rest? Suffer from headaches or migraines? Or find it difficult to concentrate all day at work? Then there’s a good chance your air at home has too much CO2, which your body releases every time you exhale. This colourless and odourless gas accumulates in the air, especially if you spend a long time in the same place or have lots of people in the same room. That’s why it’s equally important to ventilate your living room as it is to have fresh air in your meeting rooms at work.

CO2 levels can also run high in the bedroom. You exhale CO2 all night long, in a closed room of limited size. So a good mechanical ventilation system in your bedroom isn’t an unnecessary luxury. And the same applies for your office at home, where you also often spend long periods of time.

Suffering from allergies

Dust mites, pet hairs and substances in cleaning products or paint are found in lots of homes and can trigger allergic reactions, including itching and rashes or watery eyes. Your ventilation system extracts these things from the air in your bedroom, living room or other areas.

Huisstofmijt allergie

Mould in the home, on walls or ceilings

Damp indoor air that isn’t extracted quickly enough will sooner or later lead to problems. Black specks on the wall are a sign of mould forming. A powerful, preferably demand-driven, ventilation system prevents this problem. Damp air is then extracted in good time and replaced with dry air as required. An efficient solution.

An extractor fan with humidity sensor is a hero in your bathroom. A warm bath or hot shower creates vapour in the air which turns into condensation on cold surfaces around your bath or shower, such as the ceiling. So you need a system that quickly extracts moisture from the indoor air. And don’t underestimate the impact it could have in your bedrooms, too. We perspire 17 glasses a night on average, which all ends up in the air. So make sure you don’t forget your bedroom when you’re considering a suitable ventilation system.

Condensation on mirrors, windows and doors

We mention above that vapour in the air lands on cold surfaces where it becomes condensation. Even if that doesn’t cause mould to form (yet), it soon becomes annoying. Want to quickly style your hair in the mirror after a shower, but can’t see a thing for all the wetness? This is just one example of a practical inconvenience that decent bathroom ventilation will quickly resolve.

Vapour also settles on windows and walls in rooms with a lot of moisture in the air, such as bathrooms and kitchens. Consider, for example, why you open windows to air the bedroom in winter? Excessive temperature differences soon lead to damp walls, but a decent ventilation system for the bedroom can prevent this condensation from forming. And when the extractor fan in the hood above the cooker is switched off after cooking, further extraction will remove even more of any excess moisture. Quiet as a whisper, in contrast to often noisy extractor hoods, and extremely efficient. A well-designed extraction system in the kitchen will ensure you can keep a clear view of things.

Unpleasant odours

Do you sometimes notice a musty smell in your children’s bedrooms in the morning? The culprit: exhaled air, pets and odours left behind by housework, cleaning or cooking. If these unpleasant odours are not adequately extracted, they accumulate and can cause headaches and other ailments. They can even be harmful to health in the longer term.

Consider, for example, odours left behind after visiting the toilet, mist from deodorants or hairspray in the bathroom, or the smell of fried food in the kitchen or living room after a nice family meal. The boost function on a Renson® ventilation system can deal with this latter smell in the kitchen, so odours are efficiently extracted without any disturbing noise from a hood extractor. Handy.


Every project is different. The best ventilation system for your needs and wishes depends on several factors. There are central ventilation systems (A, B, C+, and D+) on the market that cover all crucial rooms in the house. But you can also use decentralised ventilation systems (in each room). So whether you’re building a new home or working on a renovation, Renson® has an effective, powerful and energy-efficient ventilation solution for every project.

System A: natural air supply and extraction

Fresh air enters the home via fitted ventilation louvres in the windows. At the same time, dirty interior air disappears outdoors through gaps and crevices. You can manually adjust how much air flows in, but regulating an A system is otherwise (too) limited. This type of ventilation is therefore outdated. It’s a basic ventilation solution. An A system is affordable and easy to install, it’s true, but warm air is extracted from inside the home along with the dirty air, while the fresh air brings the outside temperature indoors. This is, of course, no good for your energy bill, so they are no longer relevant in this day and age with strict insulation and airtightness requirements.

System B: mechanical air supply and natural air extraction

If there are no windows to incorporate louvres into, or a natural air supply lets too much noise in (e.g. from the street), then mechanical air supply is a better option. This involves a fan pushing fresh air into the home from outside, so you have natural air circulation and extraction, just like an A system. A chimney effect ensures the dirty air disappears from the home.
 But mechanical fans for supplying fresh air consume lots of energy, which is why B systems are barely used any more. This type of ventilation also makes it impossible to achieve current energy performance requirements.

System C+: natural air supply and mechanical air extraction

A C system works the other way round: a central unit mechanically extracts dirty indoor air from all the wet areas via extraction louvres. The force of extraction creates negative pressure, which allows fresh outdoor air to flow in naturally via vents fitted on top of windows. This fresh air then finds its way into every room via louvres or gaps at the bottom of internal doors.

A classic C system ventilates all the time and makes no distinction between different rooms, which there is often no need for. A C+ system, which is the smart variant of a C system, adds demand-driven operation. It starts working automatically when it detects (via its sensors) too much moisture, odours, or CO2 in the indoor air, but only to get that interior air back to the desired level in the room where it is needed, e.g. in the bathroom when you have a shower or bath, or when the whole family is in the living room. Similarly, it only switches on at night in the bedroom. So people living there don’t even have to think about it.


For Renson®, the Healthbox 3.0 ventilation unit is the beating heart of an automated C+ system. It saves energy by only ventilating where necessary and switching back to basic ventilation mode as soon as the indoor air quality returns to the right level. This ensures that no heat is lost unnecessarily and the fan doesn’t operate when not required, which together makes a big difference to your energy bill. 

System D+: balanced ventilation system with mechanical supply and extraction

A D system, also called a balanced ventilation system, recuperates the heat from the extracted, dirty indoor air to preheat the fresh air supplied from outside. It works fully mechanically and automatically. The air is drawn in from outside and passes through the home via a system of pipes. There are ventilation louvres in every room, where the air from outside is blown in. Dirty interior air is in turn also extracted from the wet rooms.
The D+ system from Renson®, the Endura Delta, constantly monitors the indoor air quality. The system switches on when the CO2 level or concentration of moisture or odours exceeds the threshold, which ensures there is sufficient ventilation at all times. This therefore also works on demand. You do need to take the energy consumption of the fans and heat exchanger into account, though. And be aware that a dual duct network requires regular maintenance and new filters.

C+ or D system?

For future-proof and durable ventilation, you need to consider a C+ or D(+) system. The more energy-efficient consumption of the C+ system largely compensates for any heat losses compared to a D system, which brings the cost of both systems much closer together than you might initially think.
 So how do you determine which system best suits your needs? Take these important differences into account:

  • In a D+ system, the air supplied from outside is filtered, which is handy if you live in a city where the air is often more polluted. If you live in the countryside, however, then a C+ system is the recommended solution.

  • A D system uses heat from the extracted air to acclimatise the fresh air from outside. This results in added comfort indoors because you don’t notice any temperature fluctuations.

  • If you spend a lot of time at home, then a D+ system is a good choice. But if everyone is at work or school during the day, a C+ system is a more energy-efficient option.

  • C+ requires less maintenance than a D system, for which you need to check the filters twice a year, among other things, and replace them if necessary. Note: periodic maintenance of ventilation systems is important to keep them operating optimally.

  • With a C+ system, ducts only need to be installed for extracting dirty interior air, and not for supplying fresh air from outside (which comes in through window vents on the tops of windows). If you’re planning a complete renovation or a conversion which involves replacing the windows, then this is the most recommended ventilation solution.

Centralised versus decentralised system

In addition to the four types of centralised ventilation systems, a decentralised ventilation system is also an option, especially if you’re only dealing with one room in the home. Renson® has brought this system up to present-day standards with Waves. The Waves system monitors humidity, CO2, and unpleasant odours in the indoor air (just like the Healthbox in the C+ system) and constantly adapts its level of ventilation to guarantee optimal air quality.
 It’s a compact and easy-to-install alternative for effective ventilation in a specific room you are refurbishing, or a smart alternative to conventional extractor fans in the bathroom or toilet, which are often operated by motion detectors or light switches. The decentralised Waves system is also an ideal solution for (small) renovations. If you’re working on a new-build project or extensive conversion, you’re better off opting for a centralised system.


In order to provide targeted and effective ventilation, you need a clear picture of the existing air quality in the home. And Renson® monitors the significant aspects of this air for you. The Sense CO2 monitor monitors current CO2 levels. If the device turns orange or even red, it’s time to take action and ventilate. And if the indoor air quality needs improving, you should invest in a reliable ventilation system that’s built to last. It’s useful to first check exactly what the problem is before looking for the right ventilation solution in a more targeted way. Because knowledge is power!

Lieven Depraetere
Author: Lieven Depraetere

Lieven Depraetere obtained his degree in architectural engineering at KU Leuven. He has a major stake in the innovative development of Linarte and Linius façade cladding at Renson.

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