•A new construction of rotary heat exchanger with bypass dampers.•Thermal behaviour of rotary heat exchanger with bypass dampers.•The effect of bypass opening on pressure loss of heat exchanger.•Energy savings potential of rotary heat exchanger with bypass dampers.•Economic benefit – return on investment. The article deals with the possibilities of using a bypass damper in a rotary regenerative heat exchanger for heat recovery in ventilation and air conditioning system and calculates the energy savings related to overcoming the pressure loss of the exchanger. For the purposes of the analysis, a prototype heat exchanger with a wheel diameter of 1000 mm and bypass damper with a diameter of 200 mm was designed and constructed. The exchanger was subjected to an experimental investigation in order to determine its behaviour. The pressure loss of the exchanger, depending on the air flow rate, as well as the pressure loss for three nominal air flow rates, depending on the opening of the bypass damper, were measured. The measurement showed that the new exchanger design enables a reduction in the pressure loss of the exchanger by up to 49% compared to the original value. Based on the measured values, an analysis of the potential savings of electrical energy for driving fans in various European cities was carried out. The energy savings depend on the given climatic location where the exchanger will be used and on the operating time of the air handling unit. From the analyses carried out, it is clear that, by including the bypass damper, 18 to 44% of the electrical energy of the fan can be saved, which overcomes the pressure losses of the heat exchanger. Based on the current electricity prices, the return on the investment for the bypass damper was calculated based on the price of electricity at the given time and place (Prague - Czech Republic, 2022), which is from 0.5 to 3 years, depending on the type and period of operation of the air handling unit equipment, at common air velocities.