Ventilation and air conditioning Good ventilation is likely to be of benefit. It reduces humidity, which in turn reduces the number of house dust mites and reduces moulds. It also helps to disperse gases produced by heating and cooking which can be a problem for some people. Although good ventilation is advised, this need not entail buying expensive equipment. In more humid parts of the world, air conditioning may be necessary to achieve the desired effect, but for the U.K. the outdoor humidity is likely to be less than the indoor, particularly in the winter months.
Some people suggest that free-standing fans or extractor fans can also increase air flow.
If a fan can be placed so that it aids airflow to and from the outside environment, without blowing allergens around within the room, then this may help. Air conditioning and ventilation in buildings with no windows are more controversial. Some researchers suggest that they merely recirculate allergens and mould spores, especially if they are not properly ventilated. Very few UK homes are likely to need air conditioning as their only means of maintaining airflow. There is almost certainly no need to have air conditioning in addition to windows and vents.