Why does my home need ventilation and what are the options?
Posted by Helena Ripley on 14 September 2015 at 3:40 pm
A house needs to be well ventilated for the comfort of its residents and to help care for the building. A house with poor ventilation can retain moisture and feel draughty or airless. Moisture can condense, leading to problems with damp, while inadequate air flow results in a build-up of indoor air pollutants from household products. It can also produce cold, uncomfortable indoor temperatures, while good ventilation can help to maintain a comfortable inside temperature and a fresh and healthy home. A whole house ventilation system is more convenient than simply opening a window or relying on draughts, because it allows you to control the flow of fresh air and does not present a security risk.
Ventilation and airtightness
Ventilation is the deliberate replacement of air in a house with fresh air from outside through, for example, open windows, trickle vents or extractor fans. Generally, you can control ventilation by closing a window or turning a fan on or off. In older houses or those with gas fires, there may be fixed vents which can’t be closed, such as air bricks.
Airtightness in a house is closely related to ventilation. It is the ease with which air is exchanged between the inside and the outside of the house through the fabric of the building, and it can’t be easily altered. The airtightness of a house is decreased by badly fitting windows and doors, because these allow draughts even when closed. Gaps or cracks in the walls or floors may be present due to age or damage, or because of poor sealing around pipes or cables that pass through walls, and will also affect airtightness.
In many houses poor airtightness provides the ventilation. That is, it accounts for a large proportion of the fresh air entering the building and the stale air escaping. However, this situation isn’t energy efficient because there is greater air exchange than is needed for good ventilation and warm air escaping from the house makes it feel cold. An even worse situation, which can occur in new builds, is if there is no air exchange at all, as the indoor air quality becomes very poor and can be damaging to health. Most houses avoid this by the use of trickle vents in windows and extractor fans in kitchens and bathrooms.
The best solution for keeping the heat in and having good air quality is to have a house that is reasonably airtight and has an effective means of ventilation.
Opening a window is a form of passive ventilation and works best if you open two windows on opposite sides of the house, either on the same floor or on the top and bottom floors, allowing the air to move freely between the two.
There are two types of passive ventilation systems: stack ventilation, driven by the buoyancy of hot air, and wind ventilation, which relies on the movement of wind outside the house. Stack ventilation can be enhanced with a solar chimney which generates a column of rising warm air, drawing in air from the rest of the house. The picture above is of a solar chimney; for information on how it works, have a look at this SuperHomes page.
Not surprisingly, this type of ventilation is driven mechanically by motors and fans. The simplest form of mechanical ventilation is the use of extractor fans combined with trickle vents in windows. Air is extracted from rooms where moisture is produced, bathrooms and kitchens. Fresh air is drawn into the house via trickle vents.
There are also centralised mechanical ventilation systems, some of which feature heat recovery. As warm air is extracted from the house it flows past cooler incoming air and heats it, reducing heat loss. This can be a key step towards trimming your energy budget.
If you are interested in seeing a domestic ventilation system in place, there are SuperHome Open Days in September 2015 where you can talk to homeowners about their experiences of mechanical and passive ventilation options.
More information about ventilation and draughts on YouGen
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