Venting An Oil-Fired System - Slant/Fin Caravan LDWO-1100-3-6 Application Manual

VENTING AN OIL-FIRED SYSTEM

A boiler venting system provides 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
regulator 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 2.
Table 2. Breeching dimensions for oil-fired systems —
LDWO Series
No. of
Model No. *
Modules
LDWO-600-2-5 2
LDWO-750-2-6 2
LDWO-850-2-7 2
LDWO-900-3-5 3
LDWO-1100-3-6 3
LDWO-1300-3-7 3
LDWO-1700-4-7 4
LDWO-2100-5-7 5
LDWO-2500-6-7 6
LDWO-2900-7-7 7
LDWO-3400-8-7 8
* 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.
Minimum
Area
Breeching Breeching
(sq.in.)
Diameter Length
11" 84 4'8"
12" 101 4'8"
13" 115 4'8"
13" 123 7'1"
14" 148 7'1"
15" 170 7'1"
16" 189 9'6"
18" 233 11'11"
19" 277 14'4"
21" 320 16'9"
22" 365 19'2"
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 3.
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 2. 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 9). The use of a vent cap where
permitted by code gives additional protection against adverse
wind conditions and precipitation.
Table 3. Chimney requirements
No. of
Model No. *
Modules
LDWO-600-2-5 2
LDWO-750-2-6 2
LDWO-850-2-7 2
LDWO-900-3-5 3
LDWO-1100-3-6 3
LDWO-1300-3-7 3
LDWO-1700-4-7 4
LDWO-2100-5-7 5
LDWO-2500-6-7 6
LDWO-2900-7-7 7
LDWO-3400-8-7 8
* 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. They are
based on use of type "B" double wall vents, connector and manifolds; 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 1988 ASHRAE Equipment
Handbook and Chimney Manufacturers Sizing Handbook.
Sizing Breeching and Chimneys for Oil-Fired Systems
Breeching for oil-fired Caravan systems can be either constant
size or graduated. When constant size breeching is to be
installed, refer to Table 2. The use of graduated sections may
reduce breeching costs. Generally, it becomes economically
feasible to use this approach when boiler batteries exceed
four modules. In this case, each breeching section usually
serves two to four modules.
To size graduated breeching and chimneys for a Caravan oil-
fired modular boiler system, use Table 2 and 3 and the
following procedure:
7
Chimney Liner Inside Dim. †
Rectangular Minimum
L x W Height
Dia.
Inches Inches
11" 9 3 ⁄ " X 9 3 ⁄ "
4 4
12" 9 ⁄ " X 13 ⁄ "
1 1
2 2
13" 13 1 ⁄ " X 13 1 ⁄ "
4 4
13" 13 1 ⁄ " X 13 1 ⁄ "
4 4
14" 13 ⁄ " X 13 ⁄ "
1 1
4 4
15" 13" X 17"
16" 13" X 17"
18" 16 3 ⁄ " X 16 3 ⁄ "
4 4
19" 16 1 ⁄ " X 20 1 ⁄ "
2 2
21" 20 1 ⁄ " X 20 1 ⁄ "
4 4
22" 20 1 ⁄ " X 20 1 ⁄ "
4 4
Feet
20'
20'
20'
20'
20'
20'
25'
25'
25'
25'
25'