The energy performance of the Polymair® heat-recovery air exchanger has been evaluated in a finisher hog unit floored with bedding, and in a piglet nursery, in the winter of 2003-2004. Two Polymair® systems were installed in a room containing four pens, each containing around 25 pigs. The two systems delivered maximum flow rates of 0,52m3 and 0,62m3/s. During the first 50 days, only one Polymair® system was enough to ventilate the whole room. Afterwards, the two systems ensured a flow rate of 8-9 liters of air/second/pig, with a relative humidity of 80%. This kept the bedding in good condition, avoiding the need to add new one. The two systems maintained more than acceptable ambient CO2 and NH3 emissions, and an average thermal efficiency of 49%. They allowed annual savings of $1155 on energy (considering $0,35/l of propane) and of $1125 on bedding handling labour, for a total of $2280. The nursery experiment was performed in two nursery units of 160 heads each. One was equipped with a Polymair® system delivering 0,38m3 of air/second and the other, with conventional bottom air extraction. In these two small rooms, air infiltrations made the ventilation only operate in case of excessive heat. This prevented the searchers from observing the expected 60 to 70% energy savings. When installing such a system, preventing air infiltration is vital, starting with the installation of nonreturn valves in its cold and warm air ducts, and of a humidity probe triggering device.