The chief cause of steam condensing on shop window is insufficient ventilation. In constructing shop fronts provision should always be made for an iron ventilating grating at the top of the sash as at A (Fig. 1); also for a fanlight over the door as at B (Fig. 2). The grating may be fitted with a hinged flap on the inside so that it can be closed when not required; the fanlight is hinged to the transom to fall inside on quadrants, or is fitted with gearing. The sill of the sash is prepared for the escape of condensed moisture (see D, Fig. 1); the bead which fixes the glass will intersect with the bead on the sill in the hollow, and from the outside a hole is bored and a zinc tube about | in. diameter is inserted (see dotted lines): this will carry away any water that may collect and prevent it running on to the show-board. Figs. 3 and 4 show, open and closed respectively, a glass louvre ventilator for fixing on to the plate-glass in the sash; these ventilators may be effectually used when there is no ventilator at the top of the sash.

Fig. 3.

Fig. 4. Preventing Steam Condensing on Shop Windows.