Input Calculations For Cubic Foot Gas Meters
Formula: BTU/hr = BTU/ft³ x number of cu. ft. of gas x 3600
÷ time to consume the number of cu. ft. of gas
Example: Calculating the input for a furnace operating on
natural gas is as follows:
1030 x 2 x 3600 ÷ 164 = 45,220 BTU/hr
Example: Calculating the input for a furnace operating on
propane (LP) is as follows:
2500 x 1 x 3600 ÷ 200 = 45,000 BTU/hr
NOTE: Do not use Mj/m³ number in the above calculations.
If the heating value is in Mj/m³, convert to English units by
dividing Mj/m³ by 0.0372816 to obtain the BTU/ft³.
Input Calculations For Cubic Foot Gas Meters
Formula: Mj/hr = Mj/m³ x number of m³ of gas x 3600 ÷ time
to consume the number of m³ of gas
Example: Calculating the input for a furnace operating on
natural gas is as follows:
38.4 X 0.1 x 3600 ÷ 291 = 47.51 Mj/hr
Then multiply Mj/hr by 0.2778 to get kW as follows:
47.51 x 0.2778 = 13.20 kW/hr
If BTU/hr is desired, multiply kW by 3412 to get BTU/hr as
follows:
13.20 x 3412 = 45,038 BTU/hr
Example: Calculating the input for a furnace operating on
propane gas is as follows:
93.15 X 0.05 x 3600 ÷ 353 = 47.50 Mj/hr
Then multiply Mj/hr by 0.2778 to get kW as follows:
47.50 x 0.2778 = 13.20 kW
If BTU/hr is desired, multiply kW by 3412 to get BTU/hr as
follows:
13.20 x 3412 = 45,038 BTU/hr
MORTEX PRODUCTS INC 501 TERMINAL RD FORT WORTH, TX 76106 Page 21
Table 3: Input Calculations For Cubic Foot Gas Meters
Table 4: Input Calculations For Cubic Meter Gas Meters
Replacing the Blower Motor
The limit switch must never be changed to a dierent
temperature setting. The limit switch is designed to
protect the heat exchanger from exceeding the maximum
allowable outlet temperature and to prevent nuisance
tripping of the limit. Changing the temperature of the limit
switch can cause either premature heat exchanger failure
which can cause personal injury, property damage, a re,
and death.
The temperature rise or the temperature dierence
between the return air and the supply air temperature
must be within the range specied on the furnace data
plate.
The supply air temperature must never exceed the
Maximum Supply Air Temperature on the furnace data
plate. The furnace must never be allowed to operate above
the Maximum Supply Air Temperature.
Operating the furnace above the Maximum Supply Air
Temperature will cause rapid premature heat exchanger
failure that can lead to holes being burnt through the heat
exchanger causing high levels of carbon monoxide to enter
the living space and/or a re. This condition can result in
carbon monoxide poisoning, personal injury, property
damage, and death.
Temperature Rise Measurement and Adjustment
The temperature rise is the supply air temperature minus the
return air temperature. The temperature rise must be within
the range specied on the furnace data plate. To determine the
temperature rise, the furnace must operate continuously for
approximately 20 minutes. Measure the temperature of the return
air (air entering the furnace) and the supply air (air leaving the
furnace). The supply air temperature can be taken either at the
plenum or at the closest register to the furnace. The return air
temperature can be taken at the furnace return air louvers or in
the return air duct. Do not try to read the temperature directly
above the heat exchangers because the radiant heat from the
heat exchangers will result in incorrect reading. The manufacturer
recommends taking the supply air temperature approximately 6
ft (1.83 m) from the furnace. The temperature rise can be changed
by increasing the blower speed to reduce the temperature rise or
reducing the blower speed to increase the temperature rise.
To avoid property damage and personnel injury, make
sure the motor leads cannot contact non-insulated metal
components of the furnace. Avoid wearing loose clothing
or any items that may come in contact with moving parts
such as the blower wheel and cause serious personal injury
or death.
1. Follow the instructions in Section 3: Startup and Shutdown
Instructions of the User Information Manual to properly shut
this furnace o.
2. Remove the louvered return air lter door located on the front
of the furnace.
3. Remove the burner compartment access panel located on the
front of the furnace.
4. Unplug the blower motor wiring harness 6-pin plug located on
the right side of the control box.
5. Remove the 2 screws on the right side of the blower mounting
plate (See Figure 15).
6. Remove the 2 screws on the left side of the blower mounting
plate.
7. Lift the blower upward while moving it to the left and pull the
blower back to remove it.
8. Label or mark the wires that are connected to the motor
terminal block with the terminal they are connected to assure
they are connected to the correct terminals on the new motor.
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