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.
British troops in a trench on the Western Front during World War I.EncyclopÃ¦dia Britannica, Inc. The typical trench system in World War I consisted of a series of two, three, four, or more trench lines running parallel to each other and being at least 1 mile (1.6 km) in depth.