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Building Design and Construction Handbook - Merritt - Ventech!

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14.20 SECTION FOURTEEN<br />

TABLE 14.3 Minimum Air Gaps for Generally Used Plumbing Fixtures<br />

Fixture<br />

Minimum air gap A, in<br />

Away from<br />

a wall*<br />

Close to<br />

a wall*<br />

Lavatories with effective openings not greater than 1 ⁄2-in<br />

diameter<br />

Sink, laundry trays, <strong>and</strong> goose neck bath faucets with effective<br />

1.0 1.50<br />

openings not greater than 3 ⁄4-in diameter<br />

Overrim bath fillers with effective openings not greater than 1-in<br />

1.5 2.25<br />

diameter<br />

Drinking fountains with a single orifice not more than<br />

2.0 3.00<br />

7 ⁄16 in in<br />

diameter or multiple orifices with a total area of 0.150 in2 (area<br />

of a 7 ⁄16-in-diameter circle) 1.0 1.5<br />

Effective openings greater than 1-in † §<br />

* Side walls, ribs, or similar obstructions do not affect the air gaps when spaced from inside edge of<br />

spout opening a distance c greater than three times the diameter of the effective opening for a single wall,<br />

or a distance greater than four times the diameter of the effective opening for two intersecting walls (see<br />

figure).<br />

† Vertical walls, ribs, or similar obstructions extending from the water surface to or above the horizontal<br />

plane of the spout opening require a greater air gap when spaced closer to the nearest inside edge of spout<br />

opening than specified in note* above.<br />

‡2 � effective opening.<br />

§3 � effective opening.<br />

when the basic fixture is a lavatory served by as 1 1 ⁄4-in trap, the average flow during<br />

discharge is 7.5 gal/min. So a bathtub that discharges 15 gal/min is rated as two<br />

fixture units (2 � 7.5). Thus, a tabulation of fixture units can be set up, based on<br />

an assumed basic unit.<br />

A specific number of fixture units, as listed in Table 14.4, is assigned to each<br />

type of plumbing fixture. These values take into account:<br />

• Anticipated rate of water flow from the fixture outlet, gal/min<br />

• Average duration of flow, min, when the fixture is used<br />

• Frequency with which the fixture is likely to be used<br />

The ratings in fixture units listed in Table 14.4 represent the relative loading of<br />

a water-distribution system by the different types of plumbing fixtures. The sum of

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