Warm air curtains and ceiling convectors A powerful stream of air instead of a solid door Door curtains drive a powerful stream of warm air across an open doorway. The air stream tempers and reduces the inward draught of cold air. Door curtains make life far more comfortable in busy locations such as shops, factory loading bays, and public buildings, where doors remain open for long periods. A curtain as well as a heater A door curtain forms a barrier to resist the ingress of cold air. Although the door curtain can contribute to the heating of a building, its primary function is as a thermal replacement for a solid door. In theory, a door curtain can shut out all draughts through an open door. The efficiency of the seal depends on many factors (power and angle of the air stream, maintenance of a laminar air flow across the open doorway, size of doorway, degree of turbulence at edges, pressure difference between the exterior and interior environments, exterior wind velocity), some of which vary, not just from day to day, but from hour to hour. In practice, a door curtain rarely forms an impervious barrier. Turbulence can never be eliminated completely, while winds and pressure differences are often too strong for the door curtain to withstand. Many door curtains therefore double as convector heaters. The curtain of warm air repels most draughts, while warming up those that succeed in passing through. The inflow of warm air that results contributes to the internal heating of the building. If you cannot see the menu, please click here