With these simple forced-air units, you can keep one or two rooms well ventilated on warm nights when your home must be closed tightly during blackout periods. Where possible, the unit containing the fan is located at the bottom of one window to draw in air from the outside, and the other unit is located at the top of a second window to permit escape of air. If only one window is available the units are located at the top and bottom of it. Each unit consists of a wood box open at opposite sides, and made to fit snugly into an opening, which is provided by raising or lowering | the sash. In Fig. 3, notice that the upper unit is held in place by angle brackets screwed to the window trim, cleats being screwed to the top of the unit to fit snugly against the sash parting stop and to the underside to fit against the lowered sash. An opaque shade to black out the window is suspended from this unit with a 6-in. drop between it and the sash to help trap | any light that might escape around the shade roller. The shade slides in grooves provided by screwing wood strips to the window trim as in Fig. 2. The lower unit rests on the window sill and has an adjustable wing on one end to fit behind the parting stop, Fig. 1. The fan-mounting board projects to fit behind the sash and a strip is provided in front on which to hook the bottom of the opaque shade. Each unit has two baffles inside to serve as light traps. The upper one has louvers at the open sides for the same purpose. A screen behind the louvers at one side keeps out insects. The lower unit has louvers at the inner side only. The side that projects out of the window is fitted with a hoodlike frame having a screened opening on the underside to prevent rain and insects from being drawn in when the fan is running.