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Minimum Clearance to Filter

There is not a single answer to minimum clearance above the filter on the top of a top inlet unit. As a general rule, there should be 6” clear from the filter to the closest obstruction. However, you can blow air directionally, but you cannot suck air directionally. Consequently, if there is a lot of opening around the sides, the top clearance may work fine at less than 6 inches, but sound must also be considered.

The top inlet, whether with or without the Q boot option, does not change the radiated sound power out of the unit. It may affect the sound pressure in the room by allowing some of the sound to be dissipated or attenuated in the ceiling cavity. The more clearance above the unit and the more open area around the sides of the unit, the better this will perform. Less clearance or tight closed-in spaces above the induction inlets will attenuate less sound and less NC reduction will occur.

Both of the issues described here are job specific. There is no real answer for clearance to fit all situations. A good general rule is 6 inches clear above the filter, but this might have to be changed or experimented with in different applications.

Source: Nailor Product Bulletin, April 21, 2002

Product: Fan Powered VAV Terminal Units With Top Induction Inlets