How to fit domestic ventilation systems

Lingering cooking smells and an excessive amount of steam condensation create an unpleasant and unhealthy environment in the kitchen. Fitted ventilation gets round the problem, and still allows you to keep the room warm and comfortable.

With improved heating, better draught proofing and double-glazing more common today, the home or a room becomes a sort of sealed unit where internally generated smoke and steam can remain trapped.

The higher the room temperature, the larger the potential moisture content of the air and the greater the likelihood of condensation forming. This can ruin paint and wallpaper—and given time, plasterwork— in the same way as damp. In the kitchen, condensation can cause unsightly mould growths while moisture-borne particles of grease act as a breeding ground for germs.

Raising the room temperature increases the moisture-carrying capacity of the air but is not in itself a successful way of preventing condensation. For this to be achieved the moisture-laden air must be carried out of the house altogether—the job of a ventilator or extractor fan.

Calculating your requirements

The cheapest form of kitchen ventilation is a self-actuating, window-mounted plastic ventilator. But although these are comparatively easy to fit, they cannot normally cope with the demands of a kitchen and some form of mechanical ventilation should be used instead.

If a combination of moisture and cooking fumes is the problem, the choice of kitchen ventilator is normally between a wall- and a window-mounted extractor fan.

Extractor fans blow stale inside air to the outside. Unless draughtproofing is completely efficient —a most unlikely possibility—this air is replaced by seepage into the kitchen from elsewhere. Between ten and twenty ‘air changes’ an hour are considered necessary for a kitchen. The lower figure applies when the room temperature is high and the cooking times are short, the higher figure when the kitchen is particularly cold or hot and steam and fumes are obviously troublesome—such as when cooking for several people.

One air change is equivalent to the volume of a room, so to help select the right extractor fan calculate your kitchen’s volume and multiply this by between ten and twenty, as outlined, to find the hourly capacity required. Divide this figure by sixty if a fan’s capacity is quoted in minutes. Always err on the side of a more powerful machine if in doubt.

If draught-proofing is efficient, an extractor may reduce the air pressure in the kitchen to a point where the efficiency of the fan is impaired. The problem can be made even worse by having a fuel burner in the room. To get round it, you must fit an air inlet, preferably as far from the extractor fan as possible.

If cooking fumes alone need to be removed, an extractor hood mounted above the stove may provide adequate ventilation. This can be either of the recirculating type—where steam-borne grease and smoke are filtered out before air is returned— or an extractor type where partly-filtered air is ducted to the outside.

The latter type is considered more efficient, though installation procedures are more involved.

Heat, too, is expelled by extractor fans but this should not be much of a problem at cooking times. Recirculating cooker hoods require frequent cleaning and replacement of their filters to keep them fully efficient. Some models can be converted into extractors by fitting an optional blanking plate and duct.

Heater ventilation

If your heating system uses a fuel-burning appliance, an adequate fresh air supply to this is essential—for both good combustion and the removal of toxic waste gases.

Unless your appliance incorporates a ‘balanced flue’ which lets in as much air as it expels fumes, effective draughtproofing of a room could starve the appliance of air and cause fumes to be drawn down the flue.

Central heating appliances are often located within the kitchen area in British homes, and this is another consideration in any kitchen ventilation project. An air vent on a door, or airbrick on an outside wall close to the burner, is a simple solution which should not impede other arrangements.

Another method is to fit a ventilator plate in floorboarding close to the appliance, though this is possible only if you have a suspended floor. The grille should be placed as close to the burner as possible to prevent floor-level draughts.

At its extreme, an adequate air supply to a burner can be provided by a wall or underfloor duct linked to the outside.

Ventilation for other appliances

Another appliance that may need ducting to the outside is a clothes drier. A wall -or window-mounted extractor fan can be used as an alternative but is usually less effective at preventing condensation build-up.

The procedure for fitting a duct is the same as for a stove hood though the specific instructions supplied by the appliance manufacturer should be followed.

In the case of a clothes-drier duct, avoid sharp bends and fine-meshed grilles which may collect minute, moisture-borne fibre particles. These need cleaning from time to time in any case, so leave some access to the duct ends and make sure the outside grille can be removed for cleaning.

Fitting an extractor fan

Positioning a ventilator

You can mount an extractor fan in a convenient external wall or window. Either way, it should be located as close to the ceiling as possible, near the sink and stove but not right above these unless the window or wall here is high.

Window mounting requires that a hole be cut in the glass. Although not a difficult task accidental breakage is all too easy. Using a replacement pane with a hole cut in it by the glazier makes fan installation much easier.

A plywood board, holed and trimmed to size, can be used instead of glass, but needs to be of exterior grade plywood and to be well sealed or painted.

The appeal of window mounting is that no structural work is involved. Offset against this is the obstructed view, restricted window opening for summer time ventilation and the untidy appearance of the unit.

It takes a little longer to install a wall-mounted fan but the additional effort is usually considered worthwhile. The necessary removal of inner and outer brickwork is not a difficult job for the handyman.

The hole should not be made any nearer than two bricks’ lengths to a wall edge otherwise structural weakening may occur. In the case of a cavity wall, a liner must be used to seal off the cavity or fumes and moisture will be expelled into it.

Extractor fans are also used to give ventilation to internal rooms. Do not be tempted, though, to have the outlet from a fan discharge into an unused chimney flue—this is likely to cause condensation problems.

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