text: Modern buildings comply with the highest energy standards and are therefore virtually airtight. This is why humidity, carbon dioxide and bad odours can no longer escape. In this case, a permanently installed ventilation system provides ideal air exchange - both in winter and in summer. The system referred to as heat recovery ventilation uses pipes to remove used air while supplying the rooms with fresh, filtered outdoor air at the same time. FRÄNKISCHE's system for heat recovery ventilation is termed profi-air.