There are several sources for tramp air leaks. Many furnaces have radiant support
guide pins through the floor and tube supports through the roof of the firebox. During
normal operation the tubes expand and contract, moving the insulation around these
penetrations. Many times, during a coil retube or other maintenance, this insulation is
removed. If these gaps are not sealed back properly, tramp air will increase leading to a
loss of efficiency.
As discussed earlier, modern convection sections could have over 40 rows of tubes,
with six to eight pass arrangements, which lead to over 240 tube penetrations through the
convection wall. These tubes expand and contract horizontally during normal operation.
It is important to seal these penetrations and inspect the seals frequently. These seals are
typically overlooked during routine furnace maintenance.
Another major source of tramp air is peep doors in the firebox. For furnace
monitoring, multiple peep doors—typically 48 or more per furnace—are provided along
the length of the firebox and in the end wall at multiple levels. These peep doors are used
every day and need to be sealed completely. Attention must be paid to the peep door
design, insulation, and sealing to ensure that the doors do not act as a source of tramp air
infiltration.
In boilers, too, unwanted air can infiltrate into the combustion chamber from cover
leaks, observation ports, gaskets, and other openings that are not sealed properly. Since
fuel must be supplied to heat up the unwanted air that is not used for combustion, this in
turn will lead to lower boiler efficiency.