Installation Quick Tips - Bth 199 And 250 Gas Pressure - A.O. Smith BTH 120 Series Service Handbook

2. "Clock" the meter as in step (2) above.
3. Repeat steps (1) and (2) until the specified input rate is achieved.
4. Turn the manual gas control valve to "OFF". Replace the pressure regulator cover screw. Remove
the pressure gauge or manometer from the manifold pressure tap and replace the set screw in
the manifold pressure tap. If the gas pressure regulator cannot be adjusted to give the full input
rating with sufficient gas pressure at the valve, check to ensure the unit is equipped with the correct
orifice. Refer to "ORIFICE CHART – BTH 120 thru 500" on Page 35.
INSTALLATION QUICK TIPS – BTH 199 AND 250 GAS PRESSURE
ADJUSTMENT PROCEDURE: MANIFOLD GAS PRESSURE BTH 199 AND 250 MODELS
IMPORTANT NOTE:
THE BTH 199 AND 250 MODELS INCORPORATE A NEW GAS CONTROL, WHICH OPERATES AT A
MANIFOLD PRESSURE OF 0" w.c. (0 kPa) FOR BOTH NATURAL AND PROPANE GAS. SEE THE "GAS
PRESSURE SPECIFICATIONS" TABLE ON PAGE 4. THESE MODELS ARE CONFIGURED PRIOR
TO BEING SHIPPED FROM THE FACTORY AND NO ADJUSTMENTS ARE NECESSARY PRIOR TO
STARTUP. THE CONTROLLER MONITORS THE AIR FLOW AND MAKES ADJUSTMENTS TO THE FAN
SPEED WHICH, IN EFFECT, CONTROLS THE AMOUNT OF GAS FLOW. THEREFORE, THE UNIT WILL
SELF ADJUST TO ACQUIRE THE CORRECT AMOUNT OF INPUT.
Supply gas pressure to the water heater must not exceed a maximum of 10.5" w.c. (2.62 kPa) for natural
gas, or 14" w.c. (3.49 kPa) for propane. The minimum supply gas pressure is 4.8" w.c. (1.20 kPa) for
natural gas and 8.5" w.c. (2.12 kPa) for propane gas.
Once the unit is installed and filled with water and the inlet pressures confirmed, simply turn the switch
on and observe operation. Cycle the unit off and on several times to ensure proper operation. For more
information please refer to the Instruction Manual.
HIGH ALTITUDE INSTALLATION
The BTH 199 and 250 models are suitable for installation up to 10,100 feet above sea level with no
adjustments.
GAS ORIFICE
The BTH 199 and 250 models do not have a natural gas orifice. A .230" orifice is used on Propane (LP) gas
models.
Gas Control Without Orifice Natural Gas
A supply gas pressure regulator (service regulator) must be installed on the gas supply line no closer
than 3 equivalent feet (1 meter) and no farther than 8 equivalent feet (2.4 meters) from the water
heater's inlet gas connection if the gas pressure is above maximum pressure or not stable.
Venturi
Gasket
w/o Orifice
Servicing should only be performed by a Qualified Service Technician
Gas Control with .230" Propane (LP) Orifice
Venturi
Gasket
w/LP Gas
Orifice
(.230")
Brass
7