The Homevent systems, by using the principle of variable air volume, provide sufficient air changes in a building to ensure humidity levels remain low enough to prevent the formation of condensation. The basic Homevent system intended for pitched roof buildings consists of a fan unit which is typically installed over the landing, drawing warmed air from the roof space and distributing it through the dwelling. The Homevent/F incorporates a heat exchanger and is designed for fiats, and maisonettes; this unit is intended to be installed in an outside wall, typically in a kitchen or bathroom and has combined intake and extract grilles at each end of the combined heat exchanger/fan unit. The heat exchanger will transfer 80% of heat contained in the extracted air to the induced air. During normal operation, the unit provides trickle ventilation but, under the control of a humidistat, it switches to boost operation to extract moist air. The moist warm air is sucked into the unit parallel to the wall surface while the warmed fresh air is directed to the centre of the room. Also available is a range of axial fan units available in 2 sizes, intended for ventilation and humidity control in bathrooms and kitchens. The units can be wall or window mounted and are controlled either manually or by an integral humidistat. In addition Haynes Manufacturing can design, supply and install light commercial ventilation for clubs, offices and shops. The company can also supply a range of roof and tile vents for use in pitched roof; models are available which can be connected to soil pipe duct-work.