Owner's Manual
17
2.7.1 If the minimum ceiling height is available, proceed
to size the common vent CV in Figure 2-13. Enter
the left hand column at the desired total input and
move right to the column corresponding to your
H, least total vent height, and read the diameter of
the common vent. If more than one elbow is used,
increase CV by one pipe size for each elbow more
than one. Proceed to size the connector rise diameter
CN by entering Figure 2-14 at H available and move
right to the column headed F. On the line for available
connector rise move right to the CN columns headed
by the module sizes selected in 2.4 above. Read the
connector diameter(s). Record these sizes on the
plans of the boiler room.
2.7.2 If a tapered or graduated manifold vent is desired, use
the same procedures above for sizing the intermediate
manifold diameter but for the total input of the
modules served by intermediate tapered or graduated
manifold vent.
2.7.3 Within Figure 2-12 are several entries of NR.
This means that the combination involved is
not recommended. The most common reason
for a combination to be designated NR is that
condensation inside the vent pipe is likely to occur.
This is particularly true of single wall vent pipe.
Combinations outside the shaded area in Figure 2-13
are also not recommended for single wall vent pipe.
Additionally, single wall vent pipe should not be
used with ve or more modules because the dilution
from the unred modules plus the lower surface
temperature of single wall pipe makes condensation
and the resulting corrosion very likely.
2.8 If a masonry chimney is desired, the minimum cross
sectional area of the chimney is found in Figure 2-15
as a function of the vent diameter. Figure 2-16 shows
the area of standard chimney tiles by size.
2.9 The following is an example of the recommended
design procedures.
Example: A 3 story apartment house needs a total
boiler capacity including service water hating, of
1,849,500 Btu/Hr net rating. The boiler room is in
a one story added portion of the building, of non-
combustible construction, similar to Figures 1-6 or 1-7
and is 20 feet long, 10 feet wide with a clear ceiling of
12 feet. No chimney is provided. Select and size the
vent system.
1) Refer to Figure 2-1 to convert net rating to input.
Input = 1,849,500 x 1.44 = 2,663,280 Btuh = 2,663
MBH.
2) From Figure 2-2 nd the closest recommended
module combination having an input of 2663
MBH. It is found that an input of 2710 MBH is
the closest size and is composed of ve 809HE and
one 808HE modules.
3) Sketch approximate module locations on the boiler
room plans using minimum clearances recommen-
ded in 2.4 above. In this case there is space to
lay-out the ve modules in line along one wall on
40” centers with ample service clearances, front,
rear, and sides, per Figure 2-10.
4) Determine the ventilation areas required from
gure 2-11. It is a conned space but outdoor air
is readily available through vents in the exterior
wall. Use the equation for Conned with Outdoor
Vent:
MBH Input = 2,710. = 677.5 sq. in.
4.0
of free ventilation area required.
5) Select the type of vent system – individual or
combined.
For an individual vent system use Figure 2-12 to
determine the vent size(s). In this example, the
height of drafthoods above the oor = 32½” +
33½” = 66” = 5½ feet. The least total vent height
is calculated from the drafthood up to the top of the
vent pipe which must be at least two feet above the
roof.
12 Ft. Ceiling Height
- 5½ Ft. Drafthood Height
+ 2 Ft. Ceiling Thickness
+ 2 Ft. Vent Extension
= 10½ Ft. total Vent Height, H
Enter Figure 2-12 at H = 10 Ft. and move right to
L = O Ft. Move right to 809HE column and nd
8” diameter for type B pipe and 10” for single
wall pipe. Continue to the right on the same line
to 809HE column and nd 9” diameter for type B
pipe and 10” for single wall pipe. Mark these sizes
on the drawing of the boiler room. If no more
than two 90° elbows are used in the system, no
corrections are necessary. The design is complete.
6) If a combined vent is desired such as in Figure 1-5,
use Figure 2-13 to nd the common vent size, CV.
Enter Figure 2-13 at 2710. MBH input. Move
right to the column H = 10 Ft. and nd common
vent diameter CV = 26” for type B pipe and single
wall is not recommended. Enter Figure 2-14 at H
= 10 Ft. and move right to F = 3 Ft. Move right
and nd connector diameter CN of 12” in the
809HE column and 12” in the 810HE column.
Calculate minimum ceiling height.
32½” Module Height
+ 33½” Drafthood Height, D
+ 36” Desired connector Rise, F
+ 26” Manifold Diameter, CV
+ 6” Clearance
= 11’2” Minimum Ceiling Height
A twelve foot clear ceiling height will work. With
only one elbow, no correction is necessary. The
design of a constant diameter manifold vent is
complete. Mark these vent and connector sizes on
the drawing of the boiler room.