Good ventilation results in fresh air indoors as well

An alternative to airing

There are many ways of exchanging air in a building. In a residential block, ventilation requirements are low and in this case airing by opening a window is the natural supplement during the warmer months. The problems occur when we need to ventilate during the cold part of the year without increasing the amount of energy we use.

Older buildings are often ventilated by means of natural ventilation based on the different densities of indoor and outdoor air. These vary with the difference between outdoor and indoor temperature, so that the ventilation airflow also varies. In simple terms, it means that cold air enters the warm building, is heated, rises and disappears through the building’s porosities. Unless there is a greater temperature difference between the indoor and outdoor environments, the air will be stationary, with insignificant or no ventilation inside the dwelling or the workplace premises as a result.

Fans replace natural ventilation

For natural ventilation to work properly, special conditions are needed which are often not possible in more modern buildings. This why more or less advanced technical systems are now used, all of which are based on fans. The simplest and most common system in single-storey detached houses or apartment blocks is extraction ventilation. This takes in air directly from outside, which is then extracted via a fan.

The choice of ventilation solution is dependent on the requirements and conditions. Important factors to bear in mind are:

• How clean is the air outside?
• Are there problems with noise from outside?
• How well-sealed/porous are the façades?
• Could draughts be a problem in winter?

Taking in air via porosities was normal in houses with natural ventilation. A disadvantage of this method is that the airflows are not controlled and energy losses can become significant. The best solution is to be able to guide the air through some type of ventilator so as to obtain ventilation that is better controlled.

Window ventilators do not work well

If you are to invest money in purchasing energy-efficient windows, you should not fit ventilators to them unnecessarily. Why? Because, as a rule, the ventilator will be detrimental to the window’s thermal insulating properties. If you find noise from outside intrusive, this type of intake air solution is even more unsuitable.

Window ventilators tend to be used on window replacement in houses with natural ventilation. Because existing wall ventilators often become blocked up when windows are replaced, the conditions for natural ventilation are no longer present, resulting in poorer ventilation. Window ventilators are usually positioned along the top edge of the window. The number of ventilators and their size must be carefully chosen to prevent problems with draughts and ensure that the air enters primarily via the ventilator. If the house’s pressure conditions change, it cannot be assumed that air will enter in this way. The more porous the façade, the greater the care needed.

Window ventilators are poor at remixing the room air and can create conditions that generate both downdraughts and draughts. Where there are problems, ventilators with thermostatic function are recommended where the opening is controlled by the outdoor temperature.

Wall ventilators usually result in fewer draughts

Wall ventilators can often be adapted to existing older intake air devices (flap valves). This type of ventilator remixes the ambient air and often directs the air towards the ceiling, which reduces any experience of a draught. In this case too, care is needed when dimensioning the number of ventilators. They are best located above the window/radiator or in corners.

Wall ventilators can be obtained with wall ducts that have some noise-reducing qualities. Whether the noise reduction is sufficient will depend on the case in question. They can also be fitted with a filter to clean dirty outdoor air.

Intake air that is heated by the radiator

The idea behind this solution is that the air is heated by the radiator before it reaches the room. This works well under normal conditions. However, if the thermostat valve on the radiator is closed during the cold months of the year, e.g. when sunlight enters the room, downdraughts can occur, as the air that enters is not heated by the radiator. The intake through the façade can be obtained in a noise-reducing version.

Which type of intake air valve is best suited in any given case depends on a number of parameters. It is therefore important that you seek the advice of an expert or a ventilation consultant before you choose an intake air device in an exhaust-air-ventilated house.