Skip to code content (skip section selection)
Compare to:

You are viewing an archived code

Appendix A
Procedures for Calculating the Minimum Sizing of the Water Supply System
For a printer-friendly PDF version of Appendix A, please click here.
   The following is a procedure that shall be used in calculating the minimum sizing of the water supply system:
Step 1.   Compute the total number of fixture units from Table 18-29-604.10.1, Demand Weight of Fixtures in Fixture Units.
   1.   For supply outlets likely to impose continuous demands, estimate continuous supply separately and add to total demand for fixtures.
   2.   For fixtures not listed, weights may be assumed by comparing the fixture to a listed one using water in similar quantities and at similar rates.
   3.   The given weights are for total demand. For fixtures with both hot and cold water supplies, the weights for maximum separate demand may be taken as three-fourths the listed demand for supply.
Table 18-29-604.10.1
Demand Weight of Fixtures in Fixture Units
Fixture Type
Occupancy Use
Valve Type
Fixture Units
Fixture Type
Occupancy Use
Valve Type
Fixture Units
Water Closet
Public
Flush Valve
10
Water Closet
Public
Flush Tank
5
Urinal 1"
Public
Flush valve
10
Urinal 3/4"
Public
Flush valve
5
Urinal Tank
Public
Flush tank
3
Lavatory
Public
Faucet
2
Bathtub
Public
Faucet
4
Shower head
Public
Mixing valve
4
Service sink
Office, etc.
Faucet
3
Kitchen sink
Hotel or restaurant
Faucet
4
Water closet
Private
Flush valve
6
Water closet
Private
Flush tank
3
Lavatory
Private
Faucet
1
Bathtub
Private
Faucet
2
Shower head
Private
Mixing valve
2
Bathroom group
Private
Flush valve for closet
8
Bathroom group
Private
Flush tank for closet
4
Separate shower 109
Private
Mixing valve
2
Kitchen sink
Private
Faucet
2
Laundry trays (1 to 3)
Private
Faucet
2
Combination fixture
Private
Faucet
3
Laundry washer
Private
Faucet
2
Bidet
Private
Faucet
2
Dishwasher
2
Drinking fountain
1/2
Laundry washer
Public
8 lbs
3
Laundry washer
Public
15 lbs
4
Water closet
Public/Private
Flushometer tank
2
 
Step 2.   Using Table 18-29-604.10.2, convert the total water demand from fixture units to gallons per minutes (gpm). Add any continuous supply demand in gpm such as lawn sprinklers, air conditioning, industrial uses, etc., to the sum of the total demand for fixtures. The result is the total required gpm demand. All distributing pipes, riser pipes and branch distributing pipes shall be sized in accordance with the demand indicated in Table 18-29-604.10.2 of this chapter.
Beyond the capacity listed in Table 18-29-604.10.2, the service pipe, main supply pipe, principal supply pipe and the branch supply pipe shall be sized to meet the velocity of water flow provisions of this chapter. Data shall be provided by the designer to substantiate this.
Table 18-29-604.10.2 – Part 1
Conversion of Total Water Demand
For Systems Predominantly Flush Tanks
For Systems Predominantly for Flush Valves
Load
Demand
Load
Demand
For Systems Predominantly Flush Tanks
For Systems Predominantly for Flush Valves
Load
Demand
Load
Demand
1
1.5
1
2
2.5
2
3
3.3
3
4
4.0
4
5
4.8
5
15.0
6
5.5
6
17.5
7
5.7
7
19.7
8
6.9
8
22.2
9
7.5
9
24.5
10
8.2
10
27.0
11
8.8
11
27.8
12
9.5
12
28.5
13
10.1
13
29.5
14
10.8
14
30.1
15
11.4
15
31.0
16
12.0
16
31.8
17
12.5
17
32.6
18
13.0
18
33.5
19
13.5
19
34.2
20
14.2
20
35.0
25
17.0
25
38.2
30
19.4
30
41.5
35
21.8
35
43.6
40
24.3
40
46.0
45
26.8
45
48.2
50
29.0
50
50.5
 
Table 18-29-604.10.2 – Part 2
Demand Weight of Fixtures
For Systems Predominantly for Flush Tanks
For Systems Predominantly for Flush Valves
Load W.S.F.U.
Demand GPM
Load W.S.F.U.
Demand GPM
For Systems Predominantly for Flush Tanks
For Systems Predominantly for Flush Valves
Load W.S.F.U.
Demand GPM
Load W.S.F.U.
Demand GPM
60
32.0
60
54.6
70
35.0
70
58.7
80
38.0
80
61.5
90
41.0
90
65.0
100
44.0
100
68.0
120
48.0
120
74.0
140
53.0
140
78.0
160
57.0
160
82.0
180
61.0
180
86.0
200
65.0
200
90.0
225
70.0
225
95.0
250
75.0
250
100.0
275
80.0
275
102.0
300
85.0
300
106.0
400
105.0
400
125.0
500
124.0
500
142.0
750
170.0
750
176.0
1,000
208.0
1,000
208.0
1,250
237.0
1,250
237.0
1,500
262.0
1,500
262.0
1,750
283.0
1,750
283.0
2,000
302.0
2,000
302.0
2,500
337.0
2,500
337.0
3,000
362.0
3,000
362.0
3,500
387.0
3,500
387.0
4,000
412.0
4,000
412.0
 
Step 3.   Determine the elevation of the highest fixture or group of fixtures or water opening above the city water main or other source of pressure supply. Multiply this elevation in feet by 0.434. The result is the loss in static pressure in pounds per square inch (psi).
Step 4.   Compute the size of meter necessary for a total water demand.
Step 5.   Compute the pressure loss through the meter. For pressure losses, consult manufacturer's data.
Step 6.   Compute the available pressure to overcome friction in the piping system. First compute all losses (see below):
1)   Subtract the above losses from the minimum service pressure in the water main or other source of supply. The remaining is the available pressure to overcome friction within an upfeed piping system.
2)   For gravity water tanks, determine the vertical distance between the incoming water service, the minimum tank water line, and the highest fixture or group of fixtures or water opening. To find the available pressure to overcome friction in the downfeed piping system, multiply the distance defined above by 0.434, then subtract the above losses from this pressure. The remaining is the available pressure to overcome friction within the downfeed piping system.
Step 7.   Compute the developed length of the basic circuit of piping from the main in the street, the house pump, the outlet side of the pressure-reducing valve or other source of supply pressure to the highest and farthest outlet.
For a gravity water tank, compute the developed length of the basic circuit of the piping from the tank connection to the highest and most remote outlet. Developed length plus 50 percent will approximate the equivalent length run (ELR).
Step 8.   Compute the pressure factor per 100 feet of developed length. From the above calculations, take the pressure available for friction loss in psi, (Step 6) divide by the equivalent length run (ELR) (Step 7) and multiply by 100 to ascertain the maximum uniform pressure loss for friction in the piping of the basic circuit. (See Table 18-29-604.10.3)
Step 9.   Knowing the permissible uniform friction loss per 100 feet of pipe and the fixture gpm and all continuous demands in gpm, the diameter of the building service and main supply pipe to the cold and hot water branch or the first branch may be obtained from Table 18-29-604.10.2.
The diameter of pipe on the coordinate point corresponding to the estimated demand and the permissible uniform friction loss shall be the size of the service and main supply pipe to cold and hot water branch or the first branch.
All other piping in the water supply system shall be sized according to the full-listed demand weight, with the exception of piping that supplies fixtures with both cold and hot water, which may be sized at three-fourths of the listed demand weight for cold or hot water piping. All continuous demands on the piping system shall be included in the fixture gpm demand.
For fixtures not listed, demand weights may be assumed by comparing the fixture to a listed one using water in similar quantities and at similar rates.
      The cold and hot water principal supply pipe, branches and risers may be obtained from either Table 18-29-604.10.3 or 18-29-604.10.4, whichever is applicable. The diameter of pipe on or directly above the coordinate point corresponding to the estimated demand and the permissible uniform friction loss shall be the size of the pipe.
No service shall be less than 1 inch nominal pipe size. Where 1 inch flushometer valves are used, the minimum size of water service shall be a 1 1/2 inch nominal pipe size and the minimum size of the riser shall be a 1 1/4 inch nominal pipe size. No riser shall be less than 3/4 inch nominal pipe size.
Table 18-29-604.10.3
Allowance in Equivalent Length of Pipe for Friction Loss in Valves and Threaded Fittings
Diameter of Fitting (Inches)
90-DEG Standard ELL (Feet)
45-DEG Standard ELL (Feet)
90-DEG Side Tee (Feet)
Coupling or Straight Run of Tee (Feet)
Gate Valve (Feet)
Globe Valve (Feet)
Angle Valve (feet)
Diameter of Fitting (Inches)
90-DEG Standard ELL (Feet)
45-DEG Standard ELL (Feet)
90-DEG Side Tee (Feet)
Coupling or Straight Run of Tee (Feet)
Gate Valve (Feet)
Globe Valve (Feet)
Angle Valve (feet)
3/8
1
0.6
1.5
0.3
0.2
8
4
1/2
2
1.2
3
0.6
0.4
15
8
3/4
2.5
1.5
4
0.8
0.5
20
12
1
3
1.8
5
0.9
0.6
25
15
1 1/4
4
2.4
6
1.2
0.8
35
18
1 1/2
5
3
7
1.5
1.0
45
22
2
7
4
10
2
1.3
55
28
2 1/2
8
5
12
2.5
1.6
65
34
3
10
6
15
3
2
80
40
3 1/2
12
7
18
3.6
2.4
100
50
4
14
8
21
4.0
2.7
125
55
5
17
10
25
5
3.3
140
70
6
20
12
30
6
4
165
80
 
(Amend Coun. J. 3-27-02, p. 82090, § 3; Amend Coun. J. 11-9-16, p. 36266, § 37)