Lennox LGM Series Manual page 32

2-Heat Exchanger (Figures 19 and 20)
The LGM units use aluminized steel inshot burners with
matching tubular aluminized (stainless steel is an option)
steel heat exchangers and two‐stage redundant gas
valves. Units are equipped with one eleven tube/burner for
high heat and one six tube/burner for standard heat. Burn­
ers use a burner venturi to mix gas and air for proper com­
bustion. Combustion takes place at each tube entrance. As
hot combustion gases are drawn upward through each
tube by the combustion air blower, exhaust gases are
drawn out the top and fresh air/gas mixture is drawn in at
the bottom. Heat is transferred to the air stream from all sur­
faces of the heat exchanger tubes. The supply air blowers,
controlled by the A55 Unit Controller, force air across all
surfaces of the tubes to extract the heat of combustion. The
shape of the tubes ensures maximum heat exchange.
The gas valves accomplish staging by allowing more or
less gas to the burners as called for by heating demand.
3-Gas Heat Exchanger Inserts
Inserts are installed on standard (130,000Btuh) and high
(180,000 Btuh) heat exchangers. Medium heat exchangers
do not require inserts. See figure 21. Inserts are used to
maintain even temperature distribution through the heat
exchanger. Temperature distribution can vary depending
on supply air flow, number of heat exchanger tubes and the
blower deck opening.
HEAT EXCHANGER ASSEMBLY
HEAT
EXCHANGER
TUBE
COMBUSTION
AIR INDUCER
GAS VALVE
BURNER
FIGURE 19
4-Burner Assembly (Figure 22)
The burners are controlled by the spark electrode, flame
sensing electrode, gas valve and combustion air blower.
The spark electrode, flame sensing electrode and gas
valve are directly controlled by ignition control. Ignition con­
trol and combustion air blower is controlled by A55 Unit
Controller.
VENT
CONNECTOR
Page 32
BURNER BOX ASSEMBLY
GAS
VALV
E
BURNERS
GAS MANIFOLD
FLAME
SENSOR
FIGURE 20
Burners
All units use inshot burners (see figure 22). Burners are
factory set and do not require adjustment. A peep hole
with cover is furnished in the heating access panel for
flame viewing. Always operate the unit with the access
panel in place.
Burners can be removed individually for service. Burner
maintenance and service is detailed in the SERVICE
CHECKS section of this manual.