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Fan coil units are available in two configurations, horizontal and vertical. The sound power levels vary with the fan capacity but in general a 3-foot (1 m) medium pressure drop silencer or equivalent is required on both the supply and return to reduce noise levels to an NC 30. Horizontal units can be located above a closet, which allows access through the closet ceiling for maintenance. Vertical units can also be placed in a closet with a silencer in the supply duct. The return can be ducted through a return-air plenum in the ceiling or through a transfer duct silencer mounted to the back of a solid core or rated door (depending on the sound power level of the unit). Lined plenum returns located beneath vertical units are usually not sufficient to achieve an NC 30, but can achieve an NC 40 to 45 in the region adjacent to the return-air grille. This may be sufficient for nonsensitive spaces but is not recommended for residential installations. Figures 16.36 and 16.37 illustrate these two types of fan coil installations.

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