John Wood Commercial - 300-400K BTU - Manual (Page 51)

51
figure 57
checking the firing rate
If firing rate adjustment is required follow these instructions to
determine the actual firing rate of the water heater:
1. Ensure there are no other gas fired appliances connected to
the gas meter firing during this test.
2. Contact the gas supplier to determine the heating value, in
btu per cubic foot, of the gas supply.
3. Connect a manometer to the manifold gas pressure tap.
Follow the instructions for Initial Start up on page 49.
4. Start the water heater and ensure it is firing.
5. Check the manifold gas pressure, refer to Table 3 on page
13 for correct pressure. See Manifold gas Pressure
Adjustment on page 50 if adjustment is necessary.
6. Locate the gas meter serving the water heater.
7. Time how long (in seconds) it takes for one cubic foot of gas
to be used while the water heater is firing with a stop watch.
8. use the formula below to “clock” the gas meter and determine
the actual firing rate of the water heater based on the heating
value (btu per cubic foot) of the gas supply:
x H = Btu/hr
3600
T
x 1050 = 300,000 Btu/hr (87.9 kW)
3600
12.6
Example:
• 3600 = seconds in one hour.
• T = time, in seconds, to burn one cubic foot of gas.
• H = heating value of gas in btu per cubic foot.
• btu/hr = actual firing rate of the water heater.
note:
1050 btu per cubic foot is a standard value for
natural gas. Standard propane gas btu content is 2500
btu per cubic foot. btu values may change in certain
areas and at high elevations. Check with the local gas
utility company.
to turn off gas
1. Change the Operating Set Point to the lowest temperature
setting, see Operating Set Point And Differential Adjustment
on page 44.
2. When the water heater has completed its shut down sequence
and enters the standby mode, turn the water heater’s on/off
switch to the “off” position.
3. Push in the gas control knob slightly and turn to the “off”
position, see Figure 56 on page 50.
4. Close the Main gas Shutoff Valve, see Figure 52 on page 36.
high altitude installations
Fire and Explosion Hazard
Gas and carbon monoxide detectors are
available.
Overfiring could result in fire or
explosion.
Under no circumstances should the
input exceed the rate shown on the
water heater’s rating label.
Breathing Hazard - Carbon Monoxide Gas
Breathing carbon monoxide can cause brain damage or
death. Always read and understand instruction manual.
Under no circumstances should
the input exceed the rate shown
on the water heater’s rating label.
Overfiring could result in damage to
the water heater and sooting.
Gas and carbon monoxide detectors
are available.
The water heaters covered by this manual are certified for use
without modification for altitudes up to 10,000 feet.
Most gas utility companies de-rate their gas for high altitudes,
making it unnecessary to install high altitude orifices.
For installations above 10,000 feet call the technical support
phone number listed on the back cover of this manual for further
technical assistance. Call the local gas or utility company to verify
btu per cubic foot content before calling for technical assistance
and have that information available.
note:
The actual firing rate of the water heater must not exceed
the input rating on the water heater's rating label under any
circumstances.
note:
Due to the input rating reduction at high altitudes, the
output rating of the water heater is also reduced and should be
compensated for in the sizing of the equipment for applications.