In an office building fresh air is normally provided by ventilation systems designed for a constant air volume (CAV). This implies that for much of the time, considerable amounts of energy can be wasted on ventilating empty offices. We have performed a simple analysis of the potential profitability of demand controlled ventilation (DCV) on a reference office building in Norway. Our calculations suggest that the maximum profitable investment in DCV equipment is about 400 EURO, per cellular office if central installations and technical areas can be reduced as a consequence of DCV. Reduced energy costs alone will cover an investment of about 300 EURO per cellular office. If the electrical energy price in Norway increases to the same level as in Denmark, reduced energy costs alone will cover an extra investment of about 700 EURO per cellular office. (C) 2002 Elsevier Science B.V. All rights reserved.