Checking The Firing Rate; High Altitude Installations - A.O. Smith BTH-120 Instruction Manual

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 52.
4. Start the water heater and ensure it is firing.
5. Check the manifold gas pressure, refer to Table 3 on page
12 for correct pressure. See manifold Gas Pressure
Adjustment on page 54 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:
3600
x H = Btu/hr
T
Example:
3600
x 1050 = 300,000 Btu/hr (87.9 kW)
12.6
• 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 47.
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. Close the main Gas Shutoff Valve, see Figure 52 on page 39.

high altitude installations

Under no circumstances should the
input exceed the rate shown on the
water heater's rating label.
Overfiring could result in fire or
explosion.
Gas and carbon monoxide detectors are
available.
Breathing Hazard - Carbon Monoxide Gas
Breathing carbon monoxide can cause brain damage or
death. Always read and understand instruction manual.
BTH 120 and 150 models are certified for use without modification
for altitudes up to 7,700 feet (2,347 m).
BTH 199 and 250 models are certified for use without modification
for altitudes up to 10,100 feet (3,078 m).
most gas utility companies de-rate their gas for high altitudes,
making it unnecessary to install high altitude orifices.
For installations above the certified elevations listed above 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.
55
Fire and Explosion Hazard
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.