Example - for a 3-bedroom, 2,000-sq.ft. home, with an exhaust-only ventilation strategy, and a target ventilation rate of 50 CFM you would need to install a 50 CFM fan with an adjustable-speed DC motor for continuous operation.
Quick Answer. Trenches were built during World War I to protect stalemated troops on both sides from artillery and rifle fire. Although the war began with rapid movement of the German army, when the Allied forces stopped the Germans, both sides dug trenches to help avoid losing territory they had gained.
trench. n. 1. A deep furrow or ditch. 2. A long narrow ditch embanked with its own soil and used for concealment and protection in warfare. 3. A long, steep-sided valley on the ocean floor. v. trenched, trenchÂ·ing, trenchÂ·es. v. tr. 1. To dig or make a trench or trenches in (land or an area, for example).