Much misinformation exists about multizone units. Yes, at one point in time, they were energy hogs, but mainly because of the older draw through cooling, blow through heating arrangement that allowed mechanically cooled air to be heated with gas or electric heat. Newer designs are not arranged in this manner, but still blend mechanically cooled with heated air potentially. This can all be avoided with proper controls and lockouts, even the use of hot gas reheat can provide some free heat during the shoulder seasons when both cooling and heating might be needed. Locking out the heating or cooling depending on ambient temperature avoids mixing heated or cooled air, but may do so at the discomfort of the space occupants. The three deck or triple deck damper is the best way to avoid mixing heated and cooled air. air mechanically cooled never mixes with air that has been heated. Either the cooled air mixes with bypass air or the heated air mixes with bypass air, but heated and cooled air never mix. By utilizing a 3-deck damper, you can minimize energy consumption. Think of the hot deck and cold deck as wells. Wells that cost money to keep filled with heated or cooled air. Every time you pull from that well, it must be refilled with heated or cooled air that costs money to do so. If you can minimize the amount you pull from the well, you minimize the energy consumed. On a traditional hot deck and cold deck multizone unit that is transitioning from full cooling to heating, you begin to pull from your hot deck well slightly, so in turn more heat must be added to maintain your well and vice versa if going from full heating to cooling, you begin to pull from your cold deck well. Another energy saving aspect is the ability to modulate both cooling compressors and gas furnaces to more closely match the required needs or amount being pulled from these “Wells”. Additional energy is saved by not overshooting heating and cooling capacities needed to maintain the hot deck or cold deck at acceptable temperatures. Rather than explain the operation in words, see our video detailing the operation and functionality of the triple deck zone damper.