Large energy and power savings can be achieved by heat recovery. The amount of energy saved in a normal air handling or ventilation is usually around 10.000 BTUH (3kW) per 1700 SCFM (at an average temperature of 46°F). Normally a single pass exchanger can provide an efficiency of 65 - 70%.

 
To achieve this you only need:

• Two air streams (exhaust and supply air) connected to one point - the exchanger.
• A heat load in the outgoing air (=higher temperature than the incoming or outside air).