Venting a oil-fired system – Slant/Fin Oil Hot Water User Manual
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VENTING A OIL-FIRED SYSTEM
A boiler venting system provides draft and an escape path for the
products of combustion. In a venting system for an oil-fired
Caravan, there are three major components: a riser with draft reg-
ulator for each module, a breeching manifold, and a chimney.
Sometimes the venting system for a boiler plant has to be
designed to compensate for inadequate chimney conditions. A
mechanical draft inducer, properly sized and installed, can usually
increase chimney capacity sufficiently to provide proper venting.
Where a draft inducer is called for, consult local codes and the
recommendations of the mechanical draft inducer manufacturer.
Normally, a draft proving device is necessary to permit operation
of the boilers only when adequate draft exists.
It is important to note that when considering a mechanical draft
inducer, the boiler room air supply requirements must be
increased. Consult the draft inducer manufacturer for this
information.
Draft Regulator
The draft regulator compensates for excessive draft that can be
caused by varying weather conditions. The regulator should be of
the barometric-draft type. Once adjusted for a particular venting
system, this type regulator automatically compensates for
excessive draft to assure optimum operating efficiency.
Breeching
Breeching is a term used to describe a manifold(s) that connects
individual boiler modules to a chimney. Breeching is usually
constructed of sheet metal having a smooth interior surface with
all joints made tight against leakage. The layout of a particular
boiler room may require that the modules be arranged in
"batteries" with rows either parallel or at right angles. Minimum
breeching sizes are given in Table 3.
To avoid creating turbulent air patterns in the breeching, it is
suggested that individual boiler vent pipes be connected to the
breeching as indicated in Figure 13.
The breeching manifold should extend into, but not beyond, the
chimney liner. Round breeching is preferable to rectangular
breeching.
Chimney
Caravan oil-fired modular boilers operate efficiently with masonry
or prefabricated chimneys. This latter type of chimney construction
is generally the least expensive.
Minimum chimney sizes and heights are given in Table 4. In
addition, the chimney should be high enough to minimize the
effects of turbulent winds and high pressure areas common near
roof-top obstructions. The National Board of Fire Underwriters
recommends that the chimney should extend 3 feet above the roof
and be 2 feet higher than any obstruction within 10 feet (figure
13). The use of a vent cap where permitted by code gives addi-
tional protection against adverse wind conditions and precipitation.
Sizing Horizontal Breeching Connectors and Chimneys for
Oil-Fired Systems
Horizontal breeching connectors shall be constant sized. The
chimney and the horizontal breeching connector are sized using
table 3.
When there are multiple banks of boilers, the horizontal breeching
connector for each bank is sized using table 3. To size the com-
mon horizontal breeching connector, add up the total input and
refer to table 3 to size.
The minimum chimney will be equal to the size of the largest hori-
zonatl breeching section connected to it.
LDWO-600-2-5
2
11"
84
4'8"
LDWO-750-2-6
2
12"
101
4'8"
LDWO-850-2-7
2
13"
115
4'8"
LDWO-900-3-5
3
13"
123
7'1"
LDWO-1100-3-6
3
14"
148
7'1"
LDWO-1300-3-7
3
15"
170
7'1"
LDWO-1700-4-7
4
16"
189
9'6"
LDWO-2100-5-7
5
18"
233
11'11"
LDWO-2500-6-7
6
19"
277
14'4"
LDWO-2900-7-7
7
21"
320
16'9"
LDWO-3400-8-7
8
22"
365
19'2"
Model No. *
No. of
Modules
Breeching
Diameter
Minimum
Area
(sq.in.)
Breeching
Length
*
Dual fuel prefix = LWDF.
Notes:
1. For breeching and chimney sizing over 8 modules, consult factory.
2. Breeching length should be as short as possible. Measurement from the
base of the vertical vent to the nearest connected appliance should be
limited to 10' or 50% of the total vent height, whichever is greater.
Table 3. Breeching dimensions for oil-fired systems —
LDWO Series
LDWO-600-2-5
2
11"
9
3
⁄
4
" X 9
3
⁄
4
"
20'
LDWO-750-2-6
2
12"
9
1
⁄
2
" X 13
1
⁄
2
"
20'
LDWO-850-2-7
2
13"
13
1
⁄
4
" X 13
1
⁄
4
"
20'
LDWO-900-3-5
3
13"
13
1
⁄
4
" X 13
1
⁄
4
"
20'
LDWO-1100-3-6
3
14"
13
1
⁄
4
" X 13
1
⁄
4
"
20'
LDWO-1300-3-7
3
15"
13" X 17"
20'
LDWO-1700-4-7
4
16"
13" X 17"
25'
LDWO-2100-5-7
5
18"
16
3
⁄
4
" X 16
3
⁄
4
"
25'
LDWO-2500-6-7
6
19"
16
1
⁄
2
" X 20
1
⁄
2
"
25'
LDWO-2900-7-7
7
21"
20
1
⁄
4
" X 20
1
⁄
4
"
25'
LDWO-3400-8-7
8
22"
20
1
⁄
4
" X 20
1
⁄
4
"
25'
Model No. *
No. of
Modules
Dia.
Inches
Rectangular
L x W
Inches
Minimum
Height
Feet
Chimney Liner Inside Dim. †
*
Dual fuel prefix = LWDF.
† Dimensions shown are from ASHRAE Guide Equipment Handbook. Also
select inside liner dimensions to give area as great or greater than shown in
this table. Chimney height is measured from the center line of the breeching
to the top of the chimney. Chimney dimensions are approximate, with no
manifold elbows or tees; and good vent construction practices. Field
conditions vary. It is doubtful that the chimney dimensions shown here will
be suitable for all applications. Consult the 2000 ASHRAE Equipment
Handbook and Chimney Manufacturers Sizing Handbook.
Table 4. Chimney requirements