A.O. Smith On Demand 305 Series 100 Design Manual page 23

IMPORTANT!
With electrical power supplied to a on-demand water heater, it will not freeze in enviornments as cold as -30 F,
when protected from direct wind exposure.
In the event of a power failure at temperatures below freezing, the water heater should be drained of all water to
prevent freezing damage.
The unit may be drained manually or through the installation of the Optional solenoid valves as shown.
The electrical connections for the two solenoid valves should be tied to the 120V power terminals provided on the
PC Board of the water heater.
When the electrical power to the water heater fails, the cold water supply solenoid valve closes, stopping the flow of
water into the heater, and the drain down solenoid valve opens, allowing the water heater and associated piping to
drain. Ensure that you run the drain for the solenoids per local codes.
Outdoor
Vacuum
On-Demand
Breaker
Water Heater
Primary
Hot Water Supply
1/4 " Minimum
Normally Open
Solenoid Valve
Route drain
per local codes
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.
Outdoor Outdoor
On-Demand On-Demand
Water Heater Water Heater
Sub 2
Sub 1
Pressure Regulator
Set to 5 PSI Below
Street Pressure
NOTE:
outside building structure. These are indicated
by being above the dashed line.
line should be located inside the building
structure.
The vacuum breaker line should be located inside
the building structure.
Domestic Hot Water - Optional Freeze Protection
6 Outdoor On-Demand Water Heater
Preferred Piping Installation
Check Valve
Pressure Relief Valve
Outdoor Outdoor
On-Demand On-Demand
Water Heater Water Heater
Pri mary Sub 1
Pressure Regulator
S
Circulating Pump
.
The Contractor or
23
On-Demand
Equipment List
On-Demand Outdoor
Water Heaters
Electronic Connection *
and Model Applicability for
electronic connection details.
Outdoor
On-Demand
Water Heater
Sub 2
NOTE:
Pipes and fittings can be
installed inside a pipe en-
closure or recess box and
packed with insulation for
additional protection.
Cold Water Supply Line
Normally Closed Solenoid Valve
(Full Size of Cold Water Supply Line)
Boiler Drain Valve
Mixing Valve
Solenoid Valve
Drawing Date:
September 07, 2008
Drawing Number:
QTY
6
Gas Supply Line
H-6-E