Updates previous Application Guides. States that the use of ceiling- mounted air terminal devices for warm air heating of perimeter zones can led to difficulties in establishing a suitable room microclimate because of downdraughts from the windows. A solution is to provide additional under-sill heating, but this is not always aesthetically desirable or practicable and there is little information to assist the designer in the selection of a suitable room air distribution system. Presents a method to assess the conditions where it is possible to provide all the heating by ceiling- mounted slot terminal devices with no additional under-sill heat source. If such a source is necessary to avoid excessive downdraught the method also indicates the required output of this source.