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Calculating WaterSense Criteria - Problem Set

Source(s) or Contributor(s)
Pacific Northwest National Laboratory
Question

For the plumbing layout below, assuming all pipes are copper M and 3/4 inches in diameter (0.824 inches for the inner diameter), calculate the theoretical volume of water stored between the water heater and the farthest fixtures, to determine if the system can meet the EPA’s WaterSense® 0.5 gallon requirement for the hot water delivery system.

*Plumbing Layout Diagram is in Image Library and the Teaching Materials tab of this Training Module

 

Table 1. Internal Volume of Various Water Distribution Piping
Ounces of Water Per Foot of Hot Water Tubing
Nominal Diameter in inches (in) Copper M Copper L Copper K CPVC CTS SDR 11 CPVC SCH 40 PEX-Al-PEX ASTM F 1281 PE-AL-PE PEX CTS SDR 9
⅜ 1.06 0.97 0.84 N/A 1.17 0.63 0.63 0.64
½ 1.69 1.55 1.45 1.25 1.89 1.31 1.31 1.18
¾ 3.43 3.22 2.90 2.67 3.38 3.39 3.39 2.35
1 5.81 5.49 5.17 4.43 5.53 5.56 5.56 3.91
1 ¼ 8.70 8.36 8.09 6.61 9.66 8.49 8.49 5.81
1 ½ 12.18 11.83 11.45 9.22 13.20 13.88 13.88 8.09
2 21.08 20.58 20.04 15.79 21.88 21.48 21.48 13.86

Source: Modified from 2009 International Plumbing Code Table E202.1. International Code Council.
January.

Conversions:   1 gallon (3.8 liters) = 128 ounces; 1 ounce = 0.00781 gallons (0.0296 liters); 0.5 gallons (1.9 liters) = 64 ounces; 0.6 gallons (2.3 liters) = 76.8 ounces