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

16

WATER CONNECTIONS

Water piping must be installed in accordance with the instructions 
in this manual and all local plumbing codes having jurisdiction. 
See Figure 7 and Figure 8 and the Piping Diagrams on page 28 as 
a reference for these instructions.

INSTALLATION INSTRUCTIONS

1. 

This HPWH unit is not designed to supply hot water directly 
to hot water fi xtures. The HPWH unit must be installed with a 
separate storage tank as shown in the water piping diagrams 
in this instruction manual.

2.  Water lines installed between the storage tank and the 

HPWH unit MUST NOT be less than the water pipe 
connection sizes on the unit. See Table 4 on page 12.

3.  The HPWH should be plumbed directly to the storage 

tank.

4.  The cold water supply must be connected directly to the 

storage tank at a low connection port on the storage tank 
on single tank and two tank preheat piping confi gurations 
for optimal effi

  ciency. See Figure 7 and Figure 8..

5.  The cold water supply MUST NOT be connected the inlet 

(entering/return) water line to the HPWH unit.

6.  The outlet (supply) water from the HPWH unit should 

connect to a middle or lower port on the storage tank.

7. 

The inlet (return) water from the HPWH unit should connect 
to a port on the storage tank lower than the outlet.

8.  A heat trap should be installed between the storage tank 

and the backup water heater on two tank preheat systems. 
See Piping Diagram on page 28.

9.  A T&P valve must be installed in the designated opening 

on the storage tank per the tank manufacturer’s requirements. 
See Temperature - Pressure Relief Valve on page 13.

10.  For optimal performance minimize the equivalent length 

of water piping between the HPWH and storage tank.

11. Building hot water recirculation loop should be 

connected to the inlet of the backup water heater on 
two tank preheat confi gurations or to the storage tank on 
single tank confi gurations. The recirculating pump MUST 
BE controlled by a fi eld supplied thermostat installed in 
the building recirculation return line near the storage 
tank or back up heater. The thermostat should stop pump 
operation the moment the recirculation line is hot.

12.  Use swing-type check valves (not spring-loaded types) on 

the water outlet lines of all HPWH units plumbed in parallel 
to prevent hot water short-circuiting.

13.  Water lines shared by parallel HPWH units must be large 

enough to handle combined water fl ows. Flow rates 
through the heat pumps and tank(s) must be balanced. 
See Table 1 on page 8 for HPWH unit fl ow rates.

14.  All components in the hot water supply system must be 

adequately sized to meet peak water fl ow requirement

15.  When the HPWH unit is installed above the storage tank 

install a Tee fi tting at a high point in the outlet water line 
leaving the unit. Install a purge valve, or if required by 
local code, a T&P valve (temperature and pressure relief ) 
in a branch of the Tee fi tting that can be used to purge 
air from the HPWH unit during start up. See Figure 7 and 
Figure 8.

16.  DO NOT install a (T&P) relief valve in the outlet line of the 

HPWH unit unless required by local code.

17.  Dielectric unions should be installed at the inlet and outlet 

water lines to the HPWH unit.

18.  All HPWH water piping must be insulated.

SINGLE TANK CONFIGURATION 

The HPWH must be plumbed to storage tank. The maximum 
stored water temperature the HPWH unit can produce in the 
storage tank is 150°F (66°C). Figure 7 shows a typical storage 
tank piping configuration. Tank ports must be large enough 
to handle the peak water fl ow rates through the water heating 
system. See Piping Diagrams on page 28 for detailed piping 
diagrams.

MULTIPLE TANK PRE HEAT CONFIGURATION

When water temperatures above 150°F (66°C) are required the 
HPWH and storage tank are piped in series (upstream) with a 
backup water heater. See Water Temperature on page 9. The 
backup water heater will raise the temperature of the 
preheated water to the fi nal system temperature required. 
Figure 8 shows a typical preheat piping confi guration.

FIGURE 7