Abstract: A filter holder is formed with a rectangular frame. The frame has two elements which are telescoped together. The filter is held within a channel when the frame is assembled. The channel is formed with a lip from each of the two elements. A retaining screen is attached to the lips of one of the elements to prevent the filter from billowing.

Abstract: A heating and air conditioning unit has a fan compartment containing a hammock-type filter. The hammock-type filter rests upon feet elevated above the bottom of the fan compartment so that air may flow into the fan through either the bottom panel of the hammock filter or either of the side panels. The front and back of channels of the bottom pannel are telescoped so that they can be expanded and always be longer than the width of the fan. Sponge rubber is provided at the front and back so that if a larger compartment is used that air leakage at the front and back is prevented by the sponge or foam rubber. The top edges of the side panels rest against the sides of the fan compartment. Foam rubber along these edges prevents noise caused by vibration as well as preventing air leakage.