Lennox LDT Series Information page 28

2-Heat Exchanger (Figure 20)
Units use aluminized steel cluster inshot burners with
matching tubular aluminized (stainless steel is an option)
steel heat exchangers and two‐stage redundant gas
valves. LDT180/240 uses two eleven-tube/burners for high
heat. LDT156/240 uses two six-tube/burners for standard
or low heat and two nine-tube/burners for medium heat.
Burners in all units use a burner venturi to mix gas and air
for proper combustion. Combustion takes place at each
tube entrance. As hot combustion gases are drawn upward
HEAT EXCHANGER
(one heat section shown)
HEAT
EXCHANGER
TUBE
COMBUSTION
AIR INDUCER
GAS VALVE
BURNER
FIGURE 20
Page 28
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 surfaces of the heat exchanger tubes. The supply
air blowers, controlled by the Unit Controller A55, 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.
VENT
CONNECTOR