![]() The WDC calculation is based, in part, on the friction losses and water velocity limitations for a given piping configuration. And a more accurate estimate of water demand allows for smaller-diameter piping to deliver the right amount of water to a home's fixtures. ![]() The IAPMO WDC method is based on up-to-date probabilities and improved statistical modeling to derive a truer water-demand estimate. (For more on the link between pipe sizing and hot water delivery delays, see “ Efficient Hot-Water Piping” by Gary Klein.) This not only wastes energy but also increases the dangers from water aging and stagnation in residential water pipes. Oversized piping can create hot water delivery delays to fixtures in the home. Hunter’s Curve grossly overestimates water demand, so plumbers routinely end up oversizing pipes. This formula does not account for today’s high-efficiency fixtures and appliances, says Dan Cole, Senior Director of Technical Services for the International Association of Plumbing and Mechanical Officials (IAPMO). The problem is that pipe sizing has traditionally been done with a fixture-unit method, which uses Hunter’s Curve, a formula plumbers have used to calculate peak water usage in single-family homes since the 1930s. ![]() According to the International Association of Plumbing and Mechanical Officials (IAPMO), which developed the app, the WDC provides as much as a 65% reduction in water demand estimates for single-family homes and multi-family units. The Water Demand Calculator (WDC), available as a smart phone app, is the first statistically-based update to sizing water supply piping in almost 90 years.
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