Donotblockcombustion-airopeningsinthefurnace,Any
blockagewillresultinimpropercombustionwhichmayresult
inafirehazardan_orcausebodilyharm
Step 2--General
This fhrnace should be installed in a location in which fi_cilities %r
ventilation permit satisfi_cto_- combustion of oil, proper venting,
and maintenance of ambient temperature at safe limits under
normal conditions of use. The location should not interfere with
proper circulation of air within the confined space. (See NFPA=3 !,
Section 1.5.)
In addition to air needed for combustion, process air shall be
provided as required for: cooling of equipment or material,
controlling dew point, heating, @ing, oxidation or dilution, safety
exhaust, and odor contml.
In addition to air needed for combustion, air shall be supplied for
ventilation, including all air required for comfort and proper
working conditions fbr personnel.
The barometric draft regulator (included with Nrnace) shall be
installed in same room or enclosure as furnace in such a manner as
to prevent any diffkrence in pressure between regulator and
combustion=air supply.
Air requirements for operation of exhaust Rms, kitchen ventilation
systems, clothes dwers, and fireplaces shall be considered in
determining the adequacy of a space to provide combustion=air
requirements.
The tack of a proper amotmt of combustion air can lead to serious
Nrnace operational problems. Some of these problems are:
1. Excessive oil burner after-drip, and oil Nines.
2. Sooting.
3. Melted oil burner ignitor/relay control.
4. Air band or air mrbulator settings more open than nom_al
5. Lockouts on start=up
The requirements _br combustion and ventilation air depend upon
whether furnace is tocated in a (ONFINED or [N(ONFINED
space.
Step a--Unconfined Space
An unconfined space must have at 1east 50 cu k for each 1000
Bmh of total input [br all the appliances (such as furnaces, clothes
dwers, water heate*s, etc) in the space.
In unconfined spaces in buildings of conventional fi'ame, brick, or
stone construction, infiltration MAY be adequate to provide air for
combustion, ventilation, and dilution of flue gases This detem?i=
nation must be made on an individual installation basis and must
take into consideration the overall volume of'unconfined space, the
number of windows and ventilation openings, the number of doors
to the outside, internal doors which can close offunconfined space,
and overall tighmess of building constluction Conside*ation must
also be given to the amount of storage items (fi/rniture, boxes, etc.)
within the unconfined space which take away l"romthe air volume
(See Table 2.)
Many new buildings and homes (and older ones that have been
weatherized) MUST BE considered as being of tight construction,
therefore, infiltration will not be sufficient to supply necessary air
fbr combustion and ventilation.
Table 2--Mimmum Floor Area
For Unconfined Space
88CMA FURNACE MINIMUM SQ FTWBTH
INPUT BTUH 7-tt2 FT CEILING
70,000 467
9%000 607
108,000 700
lt9,000 793
140,000 933
154,000 1026
A building can be considered as being of tight constluction when:
* Walls and ceilings exposed to outside atmosphere have a
continuous water vapor retarder with a rating of 1 perm or tess
with openings gasketed or sealed, and/or
* Weatherstripping has been added on operable windows arid
doors and/or
* Caulking or sealants are applied to areas such as joints around
window and door frames, between sole plates and floors,
between wall-ceiling joints, between wall panels, at penetra=
tions tbr plumbing, electrical, arid fhel lines, and at other
openings
If combustion and ventilation air must be supplied to an uncon=
fined space from outside, an opening with a FREE AREA of riot
tess than 1 sq in. per 1000 Bmh of total input of all appliances
within unconfined space (but not tess than 100 sq in.) must be
provided. This opening must be located such that it can not be
blocked at any time.
Step 4--Confined Space
A confined space has a volmne of less than 50 cu fl per 1000 Btuh
of the total input rating for all appliances installed in that space
When Nrnace is installed in a closet or enclosure, 2 ventilation
openings, with OPEN AREA as dimensioned in example below
are required for combustion air. The openings should be located
about 6 in. from top and bottom of enclosure at ti'ont of fhrnace.
(See Table 3.)
TaRe a--Combustion Air
From Confined Space
58CMA FURNACE LENGTH
INPUT NTUH {BN.)
70,000-t 0S,000 16
t19,000 20
HEIGHT
(BN.)
g
q0
NOTE: In calculating free area, consideration shall be given to
blocking effect of louvers, grilles, or screens protecting openings.
Screens used shall not be smaller than 1/4-in. mesh and shall be
readily accessible for cleaning. If free area through a louver or
grille is known, it shall be used in calculating size and free area
specified. If design and free area are not known, it may be assumed
that wood louvers have 20 percent free area and metal louvers and
grilles have 60 percent free area. Louvers shall be fixed in open
position or interlocked with fi/mace so they open automatically at
furnace start=up and remain open during It/mace operation.
The size of the openings depends upon whether the air comes from
outside of the structure or an unconfined space inside the strt/cmre.
ALL AIR FROM INSIDE THE STRUCTURE
For a confined space, where air is taken from an interior space, 2
pem_anent openings of equal area are required. One opening must
be within 12 in of ceiling arid the other within 12 in of floor. Each
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