A.O. Smith 305 Series 100 manual Tank Water Heaters in a Circulation Loop, Additional Guidelines

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 H-1-RP is an example.

The heat output of the tank must be equal to or greater than the calculated circulation loop heat loss.

(Reference page 5, 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

On-demand water heaters not recovering a storage tank: In applications involving a commercial dishwasher, a hot water circulation loop feeding the dishwasher is required.

On-demand 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 need for circulation loops to dishwashers.

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