An intervention study was performed in an office building in which there were severe indoor climate complaints among the occupants. In one part of the building a new heating and ventilation strategy was implemented by renovating the HVAC system, and a carpet floor material was replaced with a low-emitting vinyl floor; the other part of the building was kept unchanged, serving as a control. A comprehensive indoor climate investigation, including a questionnaire study of the occupants' comfort and health, was performed before and after the intervention. The intervention was performed after detailed laboratory studies on alternative flooring materials and alternative ventilation strategies. The occupants' adverse perceptions and symptoms were significantly reduced by the intervention. The improvement of the indoor climate was most pronounced in the cellular offices, where both the floor material and the ventilation and heating conditions had been changed, compared to the improvement in the open-plan offices where only the ventilation and heating system had been changed.