Burnham Series 8H/8HE Boiler Manual De Propietario
8
1.1 INTRODUCTION – The basic principles of combustion
or burning of a gaseous fuel should be reviewed briefly
in order for the reader to appreciate the necessity of:
(1) providing adequate ventilation
for replacement of
air consumed during the combustion process and the
replacement of air carried out with the products of
combustion, and (2) providing a properly designed vent
system that will effectively convey the gases produced
during the burning process to the outside atmosphere
along with any air diluting the flue gases.
1.2 COMBUSTION – In order for combustion or burning
to take place three things are needed:
1) Fuel-in this case, natural gas or propane.
2) Oxygen-oxygen is obtained from the air which is
2) Oxygen-oxygen is obtained from the air which is
approximately 20% oxygen and approximately 80%
nitrogen. Nitrogen is inert and will not burn.
3) Heat-gas will not urn until its temperature is raised
to its ignition point, approximately 1100-1200°F. A
gas burning pilot (open flame) or electrical means
(spark) is used for the initial ignition after which
the flame itself provides the heat needed to sustain
combustion.
If any of the three are taken away, combustion cannot
take place.
Because the mixing of air and fuel is not 100% complete,
more air than is actually needed called excess air must
be supplied to the appliance in order for burning to be
complete. This is shown in Figure 1-1.
If the supply of fresh air is inadequate or is not contin-
ually replenished as it is used up, carbon monoxide (CO)
and Hydrogen (H
2
) as well as the products of combustion
shown in Fig. 1-1 may be produced. This is undesirable
since carbon monoxide is toxic and some-times lethal
even in small quantities.
In addition to the fresh air required for combustion,
fresh air is also required to dilute the flue products so
that the resultant flue gas temperature is reduced to what
is considered a safe level. Thus, a total of 16 cu. Ft. of
air may be required for each cu. ft. of gas burned, 12.5
cu. ft. for the combustion process and 3.5 cu. ft. for the
dilution process.
1.3 VENTILATION – Fresh air requirements for the heating
plant will vary with the space in which the plant is located
as described and illustrated in succeeding paragraphs.
Reference to free area of air inlets is made in the text
since louvers, grilles, or screens are sometimes used at or
in the inlet and these have a blocking effect. This must
be taken into consideration in order to obtain proper
quantities of fresh air. If the free areas of these devices
are not known, it may be assumed that wood louvers will
have 20-25% free area and metal louvers and grilles will
have 60-75% free area.
For installation in boiler rooms with ventilation air
provided from inside of building having adequate
infiltration from outdoors, each opening shall have a free
area of not less than one (1) square inch per 1000 Btuh
of the total input rating of the heating plant and other
fuel burning appliance in the boiler room. See Figure
1-2.
For installation in boiler rooms with ventilation air
provided directly from outdoors, each opening shall have
a free area of not less than one (1) square inch per 4000
Btuh of the total input rating of the heating unit and other
fuel burning appliance in the boiler room. Each opening
should be equipped with a screen covering whose mesh
should not be less than ¼ inch and each opening should
be constructed so that they cannot be closed. See Figure
1-3.
Normally, if the boiler is installed in an unconfined space,
an adequate amount of ventilation air will be supplied by
natural infiltration. If however, the unconfined space is
of unusually tight construction, air from outdoors will be
needed. A permanent opening or openings with a total
free area of not less than one (1) square inch per 5000
Btuh of the total input rating of the heating plant and
other fuel burning appliances in the unconfined space
is necessary. If ducts (minimum rectangular area of 3
square inches) are used, they must be the same cross-
sectional area as the free area of the opening to which
they connect. Screening to cover the openings to the
outside should not be smaller than ¼ inch mesh and
each opening should be constructed so that they cannot
be closed. See Figure 1-4.
Adequate combustion and ventilation air must be
provided to assure proper combustion.
The importance of adequate and proper ventilation
cannot be overemphasized. It must also be
understood that venting and ventilation must always
be considered together. They are both part of the
same system and must balance each other.
If exhaust fans are utilized such as for make-up
air, the make-up air should not be drawn from the
same space that is the source of combustion air for
the heating plant unless adequate provisions are
made to supply additional outside air so that the
space surrounding the heating unit is not under a
negative pressures (less than outdoor pressure).
blowers should not be used to forcibly provide
ventilation unless controlled to a point where static
pressure in the space in which the heating plant is
located is equal to the outdoor pressure.
sEcTION 1.0 cOMbUsTION,
VENTILATION & VENT sysTEMs