A.O. Smith AHPM-270, User'S Information Manual

9

SOURCE WATER TEMPERATURE

ENTERING SOURCE WATER TEMPERATURE

The entering source water temperature range of operation for 
the unit is 40° - 100°F (4.4°C to 38°C). The source temperature 
drop (Delta T - ΔT) through the evaporator (heat exchanger) 
will be approximately 8°F to 12°F (-13°C to -12°C).

If the source water temperature is outside this operating 
range  the HPWH unit’s Limit Thermostat will discontinue 
heating operation until the entering source water temperature 
returns to this operating range. 

LOCATING THE WATER HEATER

INDOOR/OUTDOOR  INSTALLATION                                                          
(Milder Climates)

Carefully choose a location for the HPWH unit. Placement is a very 
important consideration for optimal performance and safety.

Locate the HPWH near a floor drain. The unit should be 
located in an area where leakage from the HPWH unit or the 
storage tank it is connected to will not result in damage to the 
area adjacent to the water heater or to lower floors of the 
structure. See Unit Placement on page 15.

FREEZING TEMPERATURES

The HPWH unit must not be installed in space where freezing 
temperature will occur, without a low ambient air kit. Exposure 
to freezing ambient temperatures below 32°F (0° C) may result 
in severe damage to internal components. Damage caused by 
exposure to freezing temperatures is not covered under the 
limited warranty.

COASTAL REGIONS

When the HPWH will be installed within 5 miles of a seacoast 
the optional Corrosive Duty Package is recommended. The 
corrosive duty package includes a stainless steel cabinet, 
(Ecoating is standard on the evaporator). Damage caused to 
units not equipped with the corrosive duty package in coastal 
regions is not covered under the limited warranty.

HEAT SOURCE

The HPWH unit should be located where there is adequate 
source water from which to extract waste heat and where the 
source water cooling benefi t can be utilized when possible.

INSTALLATION REQUIREMENTS

Read all installation requirements in this manual before 
installation begins.

The installation must conform to these instructions and all 
local and national code authority having jurisdiction.

Costs to diagnose, perform service and repair damage caused 
by installation errors are not covered under the limited warranty.

Costs to correct installation errors are not covered under the   
limited warranty.

WATER TEMPERATURE

MAXIMUM SYSTEM TEMPERATURE

The HPWH units covered in this manual are capable of maintaining 
a maximum system/storage tank temperature of 150°F (66°C). 
Some commercial water heating applications may require 
higher temperatures. Install a booster water heater downstream 
from the storage tank for temperatures above 150°F (66°C). 
See Figure 8 on page 17.

INLET & OUTLET WATER TEMPERATURE

The inlet (entering) water temperature operating range for 
the HPWH is 40°F to 140°F (4.4°C to 60°C). The water temperature 
rise (Delta T - ΔT) through the condenser (heat exchanger) will 
be approximately 8°F to 12°F (4°C to 7°C).

Outlet water temperatures up to 152°F (67°C) are possible 
during normal operation. Exposure to water temperatures 
this high can cause serious bodily injury or death. See Mixing 
Valves and Table 5 on pages 12 & 13.

Service & Installation Notes:

If the inlet (entering) water temperature is outside the operating 
temperature range for extended periods the control 
system may lock out on high or low refrigerant pressure 
switch events/trips.

When the control system locks out on a refrigerant pressure 
switch event the compressor will stop running, the blower and 
circulation pump (on models equipped with factory installed 
pump) will continue to operate. This is a hard lock out condition. 
The control system is manually reset by cycling power to the 
HPWH off  and then on again.

The tank thermostat must not be set any higher than 

150°F 

(66°C) to prevent control system lock outs.

Ground water temperatures can fall below 50°F (10°C) 
for extended periods during winter months in many regions. 
For this reason the cold water supply lines and should not 
be connected directly to the HPWH inlet or T fi tted into the 
inlet (return) water piping. The cold water supply lines should 
be  connected  directly  to  the  storage  tank  only.  See  the  Piping                 
Diagrams on page 28 in this manual for more information.