Specifications

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Indirect Fired Water Heaters Installation and Operating Manual
Installation & Operating Manual
How to Properly Size Your Indirect Water Heater
Use the First Hour Rating (FHR) to properly size your
Indirect Water Heater. The First Hour Rating is the amount
of hot water in gallons the heater can supply per hour
(starting with a tank full of hot water), depending on tank
capacity, source of heat, and the size of the burner.
Estimate your peak hour demand as follows:
• Determine what time of day (morning, noon, evening) you
use the most hot water in your home. Keep in mind the
number of people living in your home.
• Use the worksheet below to estimate your maximum
usage of hot water during this one hour of the day -- this
is your peak hour demand. Note: The worksheet does not
estimate total daily hot water usage.
The worksheet example shows a total peak hour demand
of 165 gallons; therefore, this household would need a
water heater with a First Hour Rating of no less than 165
gallons.
Fixture Count Guide
To quickly estimate the minimum gallons of hot water
required based on a family size number of baths and hot
water appliances the First Hour Rating of the STS tank
must be equal to or exceed the total fi rst hour
requirements.
Peak Hour Demand Worksheet
Description Fill in the Blank Example
40 Gallons for the fi rst 2 people ___________________________ Gals.
40 Gals.
10 Gallons for each additional person ___________________________ Gals.
20 Gals.
20 Gallons for each bath after the fi rst
(consecutive bath)
___________________________ Gals. 20 Gals.
10 Gallons if dishwasher is used ___________________________ Gals.
10 Gals.
20 Gallons if clothes washer is used ___________________________ Gals. 20 Gals.
TOTAL ___________________________ Gals. 110 Gals.
Heavy Usage Buffer
Use if family members take longer than average showers, etc.
x 1.5 x 1.5
First Hour Rating ___________________________ Gals. 165 Gals.
Proceed to pages 23 & 24 of this manual to locate your
Indirect Water Heater and Boiler in the sizing charts. Using
the First Hour Rating calculated in this worksheet, locate
your Indirect Water Heater and Boiler along with your First
Hour Rating. This will also determine the fl ow needed
between the Indirect Water Heater and Boiler.