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.
Deep ocean trenches are associated with subduction zones where an  ocean plate descends into the asthenosphere. The Ocean plate is  heavier than a Continental plate which ca â¦ uses the Ocean plate to  slide beneath the Continental plate. As the Ocean plate descends, a  deep ocean trench is formed. Answered.