Mixed Hot Water Capacity Calculator

Standards referenced

• DOE water conservation standards for faucets, showerheads and appliances — 10 CFR 430.32(f), (g), (o) and (p) · Maximum flow rates and water use for faucets (2.2 gpm at 60 psi), showerheads (2.5 gpm at 80 psi), dishwashers and clothes washers. These are the figures the fixture-flow defaults in the hot water demand and tankless sizing calculators reproduce.
• ASSE 1017 temperature actuated mixing valves for hot water distribution systems — Current edition · Performance requirements for thermostatic mixing valves that temper stored hot water down to a safe delivery temperature. Referenced wherever the calculators credit extra usable capacity to storing hotter than the fixtures need.
• ASSE 1016 automatic compensating valves for individual showers and tub/shower combinations — Current edition · Performance requirements for shower and tub/shower valves that limit outlet temperature and compensate for pressure changes. The delivery temperature ceilings used in the mixing calculators come from this class of device.
• ASHRAE Guideline 12, Minimizing the Risk of Legionellosis Associated with Building Water Systems — Current edition · Guidance on water temperature and system design intended to limit Legionella growth. This is guidance rather than a code requirement, and the storage and delivery temperatures quoted on this site are described as the commonly used approach and not as a requirement.
• CDC guidance on Legionella and domestic hot water temperature — Current · Public health guidance on water heater temperature, including the caution that water hot enough to control Legionella can scald and needs a tempering valve at the fixtures.