Adjustment Of Heat Input Rate - Thermo Pride MHA1-50N Installation And Service Manual

All installations and services must be performed by qualified service personnel.
B. Adjustment Of Heat Input Rate
The main burner gas orifices for this unit were selected based upon the following
assumed characteristic values of the two fuel gases suitable for use with this
appliance design:
a. For natural gas having a higher heating value of 1025 BTU per standard
cubic foot and a specific gravity of 0.60, or
b. For commercial propane gas with a higher heating value of 2500 BTU per
standard cubic foot and a specific gravity of 1.53.
The appliance rating plate inside the burner compartment will specify for which
gas the main burner orifices were selected. If the appliance is installed at an
altitude that is more than 2,000 feet above sea level, it is mandatory that the
input to the burner be reduced 4.0% for every 1,000 feet that it is above sea
level. Example: A furnace installed at an elevation of 5,000 feet, its input must be
reduced 20.0%. At 5000 ft, a total reduction of 5000 ft x 4% per 1000 ft or 20% is
required. This equates to a reduced firing rate of 80,000 BTUH (100,000 BTUH x
0.80 = 80,000 BTUH) at an elevation of 5,000 feet. (If the furnace is installed at
an elevation of 2,000 feet or less, no reduction in input rate is required.)
For high altitude installations, your local gas supplier may assist in determining
the correct main burner orifice size for the elevation at which the appliance is
installed. Our Engineering Department will gladly assist in sizing the orifice if the
lower heating value, in BTU per cubic foot, the specific gravity of the fuel gas,
and the altitude where the appliance will be installed are provided.
To check the input rate of the furnace, allow the unit to operate for 15 minutes
and proceed as follows:
1. Contact your gas supplier and ask for the BTU content (higher heating value)
of one standard cubic foot of the fuel gas supplied to the appliance at the
installation site. If the higher heating values are unavailable, it is reasonable
to assume values of 1025 BTU/cu ft, for natural gas, or 2500 BTU/cu ft, for
commercial propane gas.
2. With all other gas consuming appliances turned off and using a stopwatch,
clock the time required for the (small) dial on the gas meter to make one full
revolution. The meter dial will indicate how many cubic feet pass through the
meter during one revolution, usually one, two or five. The unit must have
been in operation at least 15 minutes before clocking.
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