Mechanical ventilation.

As insulation standards improve, heat loss by ventilation becomes a larger proportion of the total heat loss from a building. Ventilation control is therefore necessary to minimize heating energy consumption in houses. States that while passive systems and those requiring occupant participation maygive satisfactory results, only a mechanical system can provide predictable ventilation routes and rates at all times. An extract only system has low initial cost, but it is difficult to ensure fresh air ventilation throughout the rooms of the house. A complete supply and extract system with heat recovery is expensive to install and requires careful design to ensure convenient duct runs but the performance is predictable. Economics are attractive when compared with the energy loss caused by opening windows.