A.O. Smith On Demand 305 Series 100 Design Manual page 29

For this application:
Pump should be controlled by an Aquastat,
Timer or Combination Aquastat and Timer.
Pump to be sized to maintain circulation
loop temperature.
The pump should be sized to overcome the
pressure loss through the tank water heater,
and supply and return plumbing in the
circulation loop. Reference the section
Pump Sizing for Circulation.
Pump to be of bronze or stainless construc-
tion.
On-Demand
Water Heater
Primary
Hot Water
Supply Line
Building Outlets
Key
3/4" Ball Valve
3/4" Union
NOTE: This drawing is not intended to describe a complete system and is not a replacement for a pro-
fessional engineering drawing. It is intended only as a guide and does not imply compliance with local
building code requirements. Confer with local building officials before installation
engineer is to determine the necessary components and configuration of the particular system to be in-
stalled. It is the responsibility of the engineer or contractor to ensure that the installation is in accordance
with all local building codes.
On-Demand
On-Demand
Water Heater Water Heater
Sub 1 Sub 2
Pressure
Regulator Set to
5 PSI Below
Street Pressure
(Optional) Header Sized One Pipe Size Larger Than Hot
Water Supply Line - (
To eliminate cold water sandwich effect
caused by frequent On/Off operation)
Domestic Hot Water - Circulation Systems
6 On-Demand Water Heaters with Gas or Electric Tank
Preferred Piping Installation
Check Valve
Pressure Relief Valve
On-Demand
Water Heater
Primary
Aquastat Connection
Smaller Return Line
Can Be Used After
The Last Fixture
Pressure Regulator
Circulating Pump
.
The Contractor or
29
On-Demand
Equipment List
On-Demand
Water Heaters
Electronic Connection *
* Refer to On-Demand Accessories
and Model Applicability for
electronic connection details.
On-Demand On-Demand
Water Heater Water Heater
Sub 1
Sub 2
Cold Water Supply Line
Gas or Electric
Tank Water
Heater
Boiler Drain Valve
S
Solenoid Valve
Drawing Date:
September 07, 2008
Drawing Number:
QTY
6
Gas Supply
Tank Water
Heater sized
to maintain
circulation loop
temperature
Expansion Tank
Mixing Valve
H-6-RP