8
This water heater can deliver scalding water. Be careful whenever
using hot water to avoid scalding injury. Certain appliances such as
dishwashers and automatic clothes washers may require increased
water temperatures. By setting the thermostat on this heater to
obtain the increased water temperature required by these appliances
you may create the potential for scald injury.
To protect against injury, install a mixing valve in the water system.
This valve will reduce point of use discharge temperatures by mixing
cold and hot water in branch supply lines. Such valves are available
from your local plumbing supplier.
The following table details the relationship of water temperature
and time with regard to scald injury and may be used as a guide in
determining the safest water temperature for your applications.
Approximate Time / Temperature Relationships in Scalds
120
o
F
More than 5 minutes
125
o
F
1 1/2 to 2 minutes
130
o
F
About 30 seconds
135
o
F
About 10 seconds
140
o
F
Less than 5 seconds
145
o
F
Less than 3 seconds
150
o
F
About 1 1/2 seconds
155
o
F
About 1 second
F. Potable Expansion Tank
A potable hot water expansion tank may be required to offset heated
water expansion. If there is a back flow preventer or any other type
of no return or check valve in the system a thermal expansion tank IS
MANDATORY. The expansion tank must be sized for the entire water
volume of the hot water system. A weeping relief valve indicates the
need for an expansion tank. See the Typical Expansion Tank example
in the Piping section for details.
G. Pressure Drop Sizing For Circulator
The boiler circulator flow rate must meet the requirements found in
the water heater specifications, Part 2, this manual, or the published
ratings cannot be achieved. The following flow chart below
represents the pipe run, water heater, and heat exchanger ONLY and
does not include any flow checks, zone valves, or friction loss through
the boiler. That resistance must be added to the value found in the
following chart.
Pressure Drop for Pipe Length of 1” Copper,
Six 90
o
Elbows, and One Tee
Pipe Size
20’
30’
40’
50’
60’
6 GPM
8.63
8.93
9.23
9.53
9.8
7 GPM
11.3
11.77
12.24
12.7
13.1
10 GPM
10.25
11.1
11.95
12.8
13.66
12 GPM
11.3
13.2
14.1
15
16
14 GPM
15.3
16.4
17.5
18.6
19.8
Pressure Drop for Pipe Length of 1 1/4” Copper,
Six 90
o
Elbows, and One Tee
Pipe Size
20’
30’
40’
50’
60’
20 GPM
10.9
11.7
12.6
13.4
14.3
22 GPM
14
15
16
17
18
24 GPM
16.2
17.5
18.8
20.1
21.5
28 GPM
20.4
22
23.6
25.2
26.8
Table 4 - Pressure Drop through 1” and 1 1/4” Copper
Table 6 - Approximate Time / Temperature Relationships in Scalds
