Gas Line Leak Testing; Purging - A.O. Smith BTH-120 Instruction Manual

gas line connection
1. The water heaters covered by this manual are shipped
from the factory with 3/4 inch supply gas connections. The
supply gas line must not be smaller than 3/4 inch. Connect
the supply gas line to the water heater's 24 Volt Gas Valve
in accordance with all applicable local and national code
requirements.
2. Depending on the developed equivalent length and/or the
number of appliances connected to a common main, the size
of the supply gas line may have to be increased, see Gas
Line Sizing on page 39. If the supply gas line must be re-sized
larger to accommodate increased supply gas line lengths or
multiple appliances use reducer couplings and short pipe
nipples to increase the supply gas line as shown in Figure 53.
note: make the transition to the larger supply gas line as
close to the supply gas connection as possible.
INSTALL A REDUCER
COUPLING WHEN A
LARGER SUPPLY GAS
LINE IS REQUIRED
FIELD INSTALLED
PIPE NIPPLE
SUPPLY GAS LINE CONNECTION
120,000 & 150,000 Btu/hr MODELS
3. Apply thread sealing compounds (pipe dope/Teflon tape)
sparingly and only to the male threads of the pipe joints. Do
not apply sealing compound to the first two threads. Use pipe
dope or Teflon tape marked as being resistant to the action of
liquid petroleum (LP/propane) gases.
LOW GAS PRESSURE
SWITCH
COMBUSTION
BLOWER
SUPPLY GAS LINE CONNECTION
199,000 & 250,000 Btu/hr MODELS
TO MAIN
BURNER
FLOW
24 VOLT
GAS VALVE
figure 53
SUPPLY GAS CONNECTION
FACTORY INSTALLED
TEE FITTING
figure 54
4. Use only a smooth jaw adjustable wrench (such as a monkey
wrench) as a back up on the body of the 24 Volt Gas Valve
when tightening the first pipe nipple into the body of the valve.
do not use a standard pipe wrench (Stillson wrench) with
metal tooth jaws as this may permanently damage the valve.
5. Use a standard pipe wrench (Stillson wrench) as a back up
on the first pipe nipple installed above when connecting other
fittings and pipe in the supply gas line to prevent the 24 Volt
Gas Valve on the water heater from twisting during installation.
6. To prevent damage, care must be taken not to apply too
much torque when connecting the supply gas line to the
water heater.
7. Install a sediment trap as shown in Figure 52 on page 39.
8. Install a main Gas Shutoff valve in the supply gas line as
shown in Figure 52 on page 39.
note: Should overheating occur or the gas supply fail to shut
off, turn off the main Gas Shutoff valve to the water heater.

gas line leak testing

Any time work is done on the gas supply system perform a leak
test to avoid the possibility of fire or explosion.
1. For test pressures exceeding 1/2 psi (3.45 kPa) disconnect
the water heater and its main Gas Shutoff Valve from the
gas supply piping system during testing, see Figure 52
on page 39. The gas supply line must be capped when
disconnected from the water heater.
2. For test pressures of 1/2 psi (3.45 kpa) or less, the water
heater need not be disconnected, but must be isolated from
the supply gas line by closing the main Gas Shutoff Valve
during testing.
3. Paint all supply gas line joints and connections upstream of
the water heater with a rich soap and water solution to test
for leaks. Bubbles indicate a gas leak. Do not use matches,
candles, flame or other sources of ignition for this purpose.
4. repair any leaks before placing the water heater in operation.

purging

Gas line purging is required with new piping or systems in which
air has entered.
Purging should be performed per the current edition of NFPA 54
the National Fuel Gas Code.
40
Fire and Explosion Hazard
Use joint compound or Teflon tape
compatible with propane gas.
Leak test before placing the
water heater in operation.
Disconnect gas piping and main
gas shutoff valve before leak
testing.
Install sediment trap in
accordance with NFPA 54.