Climate change is already having an impact on the environment and there is no doubt that the reduction of carbon emissions is paramount if we are to help preserve the world in which we live. One way in which emissions can be reduced is by reducing energy consumption when heating and cooling buildings by incorporating heat recovery equipment. Instead of extracting the stale air and sending heated air to atmosphere energy recovery devices can be incorporated into the extract plant to recover a large proportion of the otherwise wasted heat which can then be transferred to the supply air stream.