To examine if powerful air cleaners with HEPA-filters and a pre-set speed function making it possible to run the air cleaners at a high, but noisy speed at acceptable times, and , if wanted, at a lower, but less noisy speed at other times, (Icleen IQAir®) , have a favourable effect on asthma in children and adolescents aged 8-17 years, who are allergic to dogs, but not to house dust mite. To look at this study separately, but also look upon the total results of this study and a previous study performed by the project leader.