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Determine the acceptable temperature drop at the last fixture in the loop. For example, if the supply temperature from the water heater is 120 .F (49 .C) and an acceptable temperature at the last fixture is 100 .F (38 .C) then the acceptable temperature drop is 20 .F (7 .C). 3. Calculate the required pump flow rate using the following formula: FLOW RATE (gpm) = HEAT LOSS (BTU / h) 500 X ACCEPTABLE TEMPERATURE DROP (.F ) 4. Based on the above calculations select a pump for the type of circulation system you will be utilizing: A). Preferred Method (reference drawing WH-1-RGE) - Reference pump manufacturers flow vs. pressure specifications to select a pump that can provide the flow rate calculated above while overcoming the pressure loss through: • Tank water heater (reference manufacturer’s information) • All building supply and return plumbing in the circulation loop (reference local plumbling codes, standards, or practices) B). Optional Method (WH-1-R) - Reference pump manufacturers flow vs. pressure specifications to select a pump that can provide 3 gpm of flow or the flow rate calculated above, whichever is greater, while overcoming the pressure loss through: • Tankless water heater (reference flow vs. pressure curve of the model being used) • Optional storage tank (reference manufacturer’s information) • All building supply and return plumbing in the circulation loop (reference local plumbling codes, standards, or practices) NOTE: Only use pumps of brass or stainless steel construction. Do not use pumps of iron construction as they will oxidize and clog the inlet filter on the appliance. 5 Tank Water Heaters in a Circulation Loop Tank Water Heaters in a Circulation Loop The following applies when using a tank water heater (gas or electric) to provide heat for a circulation loop. Drawing WH-1-RGE is an example. The heat output of the tank must be equal to or greater than the calculated circulation loop heat loss. (Reference page 6, Step 1 on calculating heat loss). Electric Tank Water Heater Since the input and output are the same for an electric tank water heater, this can be expressed as: Electric Tank Input (Kw) > Circulation loop heat loss (Btu/h) 3413 (1 Kilowatt = 3,413 BTU) Gas Tank Water Heater When using a gas style water heater, the efficiency of the tank must be taken into account. Available Btu output = (Btu input of tank) x (efficiency) > Circulation loop heat loss (Btu/h) Example: 30,000 Btu input gas tank 0.62 Efficiency 30,000 x .62 = 18,600 available Btu output Additional Guidelines Tankless water heaters not recovering a storage tank: In applications involving a commercial dishwasher, a hot water circulation loop feeding the dishwasher is required. Tankless water heater recovering a storage tank: In applications involving a commercial dishwasher, a hot water circulation loop feeding the dishwasher may be required depending on the distance between the dishwasher and the storage tank. Refer to local codes when determining the ne...

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