Air Cleaners for Children and Adolescents With Asthma and Dog Allergy

The purpose is to find out if Icleen IQAir, HEPA-filter air cleaners with high capacity and pre-set speed functions, have a beneficial effect on patients with asthma and allergy to dogs. Air cleaners will be installed in the bedrooms and living rooms in the homes of children and adolescents aged 8-17 years at the study entry, with allergy to dogs, but not to house dust mites. The investigators will look upon the significance of this study, and of a previous study with a similar design and the same main parameters to find out if this trial supports the results of the first trial by the same project leader, or makes it likely that the seemingly beneficial effects of the first study occurred by chance. Main parameters: * hyperventilation cold air challenge test Supportive parameters: * serum ECP * symptom scores The trial will be a parallel, double blind placebo controlled one.