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To understand how a burner operates, it is important to understand the following terms (see Figure
3-9):
Gas:
The fuel used by the burner, either natural or L.P.
Primary Air:
The air mixed with the gas in order to make the gas combustible.
Secondary Air:
The supplemental, or ambient air, surrounding the flame.
Air/Gas Ratio:
Comparison of amounts of fuel gas and air to act as primary and
secondary air.
For proper operation, a burner needs the correct amount of gas mixed with the correct amount of
air, referred to as the "air/gas ratio." A correct air/gas ratio will result in a flame that is stable without
yellow tips. The ratio depends upon the fuel gas type being used. Ten cubic feet of air are needed
to completely burn one cubic foot of natural gas (10 to 1 ratio) and twenty-four cubic feet of air are
needed to completely burn one cubic foot of L.P. gas (24 to 1 ratio). (See Figure 3-10).
When broken down, 70% to 80% of the total air required is mixed with the gas as primary air. The
remaining 20% to 30% is pulled into the flame as secondary air.
1 cu.ft.
Gas
10 cu. ft. Air To 1 cu.ft. Gas
BURNER OPERATION
Gas
Primary Air
Primary Air
1000 BTU Heat
10 cu.ft.
Air
Natural Gas
Figure 3-9
1 cu.ft.
Gas
L.P. Gas
24 cu. ft. Air
To 1 cu.ft. Gas
Figure 3-10
Page 3-8
Secondary Air
1000 BTU Heat
24 cu.ft.
Air
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