Calculate daily water consumption and hot water heating energy for commercial dishwashers and glasswashers.
Water / Hour
75 L
Water / Day
600 L
Heating Energy / Day
31.4
kWh
Heating energy = water volume × 4.186 kJ/kg·°C × temperature rise ÷ 3600. Check manufacturer TDS for actual water consumption per cycle.
Water use varies significantly by type and usage. A commercial undercounter glasswasher running 30 cycles/hr at 2.5 L/cycle uses 75 L/hr, or 600 L in an 8-hour shift. A busy hood-type dishwasher at 20 cycles/hr, 5 L/cycle uses 100 L/hr (800 L/shift). These figures are for wash water only — rinse water adds approximately 30% more.
Commercial dishwashers require wash water at 55–65°C for effective cleaning and sanitising. High-temperature final rinse models require rinse water at 82–85°C for heat sanitisation without chemical sanitiser. Low-temperature machines use cooler water with chemical sanitiser. New Zealand Food Safety requires dishwashers to meet specific time/temperature combinations.
Size the hot water system to meet peak demand — typically morning dishwashing startup and post-service rush. Add up dishwasher water demand, hand washing basins and cooking equipment (steamers, bratt pans). A buffer storage tank reduces peak demand on the heater. As a guide, allow 10–20 L/hr per cover for a full-service restaurant.