With the growing share of ventilation heat loads, the heat recovery over the mechanical ventilation systems appears as one of the key solutions to reduce heat loss and generate energy savings. Finland's long-term renovation strategy aims for a highly energy-efficient and almost carbon-free building stock by 2050. One of the greatest potentials for energy savings relates to those built between the 1960s and 1980s where no heat recovery exists. This study addresses the wasted heat potential of apartment buildings in the Kymenlaakso region in Finland and how EAHPs can utilize it. The wasted heat potential was mapped by selecting buildings of different ages in Kotka from the 1950s to 2010 and for which the thermal energy balance was determined. The apartment buildings with mechanical exhaust ventilation in Kymenlaakso were surveyed. If all the mapped exhaust air waste energy could be utilized by EAHPs, it could produce the thermal energy combined from different decades up to 18.7 GWh/a in Kotka and 36.8 GWh/a in Kouvola. The calculated annual reduction in CO2 emissions might be about 590 and 944 tCO2 in Kotka and Kouvola, respectively. The calculated payback periods varied from 7 to 13 years for the selected buildings.