Warewasher Hot-Water Demand and Booster Sizing

The two numbers that decide whether a rack comes out sanitized. A high-temp machine sanitizes with a 180 F final rinse and the building rarely delivers more than 140 F, so a booster makes up the last 40 degrees, and it must make them up at the rinse flow rate rather than averaged over the hour. The constant 500.4 is 8.34 lb/gal x 60 min/hr, so one gallon per minute raised one degree F is 500.4 BTU/hr, and the booster load is rinse gpm x rise x 500.4. A door-type machine with a 1.16 gpm rinse from 140 F to 180 F needs 1.16 x 40 x 500.4 = 23,219 BTU/hr, which is 6.8 kW, so a 9 kW electric booster covers it and a 7 kW does not once connection losses are counted; on a gas booster at 80% thermal efficiency the input is 23,219 / 0.80 = 29,024 BTU/hr. The second output sizes the building water heater instead of the booster: racks per hour times gallons per rack is the total volume the machine pulls off the 140 F system, 40 x 1.2 = 48 gal/hr here, and a machine can be perfectly boosted and still run cold because the building heater cannot keep up with that volume. A sizing screen; the machine's data plate, the local plumbing code, and the health authority's sanitizing-temperature rule govern.

delta_t_f = rinse_temp_f - supply_temp_f; booster_btuh = rinse_gpm x delta_t_f x 500.4; booster_kw = booster_btuh / 3412; gas_input_btuh = booster_btuh / booster_efficiency; hourly_hot_water_gal = racks_per_hour x gal_per_rack.

The sensible-heat relation with the 500.4 BTU/hr per gpm-degree F constant (8.34 lb/gal x 60 min/hr), against the 180 F final-rinse condition of NSF/ANSI 3 and the FDA Food Code high-temperature sanitizing requirement, cited by name and not reproduced; the machine data plate and the local health authority govern.

The heat-rate arithmetic is public physics. The rinse flow, the supply and rinse temperatures, the rack rate, and the booster efficiency are the machine's and the building's own values; the sanitizing temperature is cited to its standard, not mirrored.

Estimate. AHJ and licensed professional govern.

Field names used by the API: rinse_gpm, supply_temp_f, rinse_temp_f, racks_per_hour, gal_per_rack, booster_efficiency, delta_t_f, booster_btuh, booster_kw, gas_input_btuh, hourly_hot_water_gal

• 500.4 constant 8.34 lb/gal x 60 min/hr; one gpm raised one degree F is 500.4 BTU/hrsensible-heat relation for water
• Final-rinse temperature 180 F high-temperature sanitizing rinse, cited to NSF/ANSI 3 and the FDA Food Code, not reproducedNSF/ANSI 3; FDA Food Code
• Two separate loads the booster is sized on rinse gpm; the building water heater is sized on racks per hour x gallons per rackfood-service plumbing design practice