Draft Breaking Hood
A draft breaking hood is an open connection between the
heater tube exhaust and the exhaust stack. It allows fresh
dilution air to pass into the exhaust and mix with the
The advantages of a draft hood are:
• the burner operation is less sensitive to atmospheric
• the temperature of the exhaust gases is lower when
they pass through the roof.
NOTE: Leave access between the draft hood and the tube
exhaust. Install a damper plate if acoustic feedback
occurs in the tube.
If the immersion tube will operate at efficiencies less than
80%, the exhaust leg can be raised through the liquid
surface. For efficiencies of 80% or higher, locate the
exhaust stack outside of the tank and provide a drain. See
Figures 3.4 and 3.5.
NOTE: Regardless of the exhaust design, pitch the
immersion tube down towards the exhaust so condensate
will not collect at the burner.
■ At efficiencies of 80% or greater, low exhaust
temperatures will cause condensation to form in
the tube at start-up or during long idling periods.
The higher the efficiency the more condensation
operation, provide a condensate drain at the
exhaust and slope the immersion tube downward,
away from the burner.
Figure 3.4. Efficiencies less than 80%
Figure 3.5. Efficiencies 80% or more
Tube placement in tank
The tube placement height in the tank should be high
enough to avoid the possibility of sludge build-up on the
bottom of the tank; however, it should be low enough to
avoid tube exposure due to liquid level variations caused
by evaporation or displacement. In the latter case use a
liquid level switch to shut down the burner
Step 3: Control System
ImmersoJet burners use a modulating on-ratio control
system as shown in Figure 3.3. To control the heat
delivered by the burner, adjust the air flow to the burner.
The gas flow will change in proportion to the air flow.
The burner will operate reliably at any input between the
low fire and high fire limits stated on the burner's