609.11 Pipe Insulation.
Insulation of domestic hot water piping shall be in accordance with Section 609.11.1 and Section 609.11.2.
The water in uninsulated 1/2-inch nominal pipe surrounded by room temperature air cools down from 120°F to 105°F in about 10 minutes; in 3/4-inch nominal pipe it cools down in about 15 minutes. R-3 pipe insulation roughly doubles the cool down time to 20 minutes for 1/2-inch piping and roughly triples it to 45 minutes for 3/4-inch piping. When the time between hot water events exceeds one hour, the water in the insulated pipes is likely to cool down back to ambient, minimizing the benefit of pipe insulation for spread out draws. Based on the Lawrence Berkeley National Laboratory research findings (2012), about 30 percent of hot water draws are within 10 and 60 minutes apart. Pipe insulation will eliminate most of the water and energy wasted while waiting for these hot water draws. See Figure 609.11.
