A.O. Smith 186965-001 manual Pump Sizing for Storage Tank Application, Pump Flow Requirements

Pump Sizing for Storage Tank Application

The following applies when using on-demand water heaters to recover a storage tank. Drawing H-1-TC is an example.

On-Demand water heaters have a pressure loss which must be considered in the system design. Reference the pressure loss curve for the heater model being used to determine the pump size for the desired recovery rate.

For recommended pump sizes use the table below. Additional pressure losses in plumbing between the Heater(s) and the storage tank must also be taken into consideration.

The specified pump size is to provide maximum recovery of the storage tank. A smaller pump size may be used, but could result in longer recovery time of the tank. Please contact the Tech Services department with any questions on pump sizing.

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.

Pump Flow Requirements

Number of
On-Demand	705/505	305
Water Heaters
1	6 gpm @ 30' head	5 gpm @ 25' head
2	12 gpm @ 30' head	10 gpm @ 25' head
3	18 gpm @ 30' head	15 gpm @ 25' head
4	24 gpm @ 30' head	20 gpm @ 25' head
5	30 gpm @ 30' head	25 gpm @ 25' head
6	36 gpm @ 30' head	30 gpm @ 25' head
7	42 gpm @ 30' head	35 gpm @ 25' head
8	48 gpm @ 30' head	40 gpm @ 25' head
9	54 gpm @ 30' head	45 gpm @ 25' head
10	60 gpm @ 30' head	50 gpm @ 25' head
11	66 gpm @ 30' head	55 gpm @ 25' head
12	72 gpm @ 30' head	60 gpm @ 25' head
13	78 gpm @ 30' head	65 gpm @ 25' head
14	84 gpm @ 30' head	70 gpm @ 25' head
15	90 gpm @ 30' head	75 gpm @ 25' head
	Table “C”

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