19
must be 15" in diameter. For Section B size, go down to
3 modules, where you’ll find that Section B must be 12"
in diameter. Where the two breeching sections are con-
nected, a 12" to 15" tapered increaser must be used.
Rectangular Breeching:
Where necessary to use rec-
tangular instead of circular breeching, the larger dimen-
sion of the rectangle must be in the vertical, as shown in
Figure A4, MG-2310A heating plant example. For the
breeching division sizes from Figure A2, Section A is 194
square inches and Section B is 124 square inches. Size
of the rectangles will be about 15" high by 13" wide for
Section A and 12" high by 11" wide for Section B.
CHIMNEY SIZING
As a reminder, if the existing chimney will be used for the
new heating plant, it cannot be assumed that chimney
size is adequate. Chimney size must be based on the
chimney’s capacity, which involves several factors, the
first of which is the chimney’s capability to handle the
heating plant Btuh input capacity that is to be vented into
it. For example, a six-module MG-2310A heating plant
has a Btuh input of 2,382,000; therefore, the chimney
must be sized to handle a minimum of 2,382,000 Btuh.
However, if the installation has two MG-2310A heating
plants vented into the same chimney, then the chimney
capacity must be 4,764,000 Btuh input.
Chimney capacity is directly related to what’s connected
to it - the chimney does not function on its own, but op-
erates in conjunction with the breeching and equipment
connected to it. Another important factor is draft loss;
equipment and breeching must be located as close as
possible to chimney to minimize draft loss. Equipment
located further away from the chimney will have greater
draft loss, necessitating a chimney with a greater capac-
ity to accommodate the greater draft loss.
Chimney capacity also varies with its height and inside
diameter. The higher the chimney, the greater its capaci-
ty; the larger the inside diameter, the greater its capacity.
Any two different size chimneys can have equal ca-paci-
ty; that is, a short chimney with a larger inside diameter
can have the same capacity as a higher chimney with a
smaller inside diameter.
Chimney height determines the total draft which can be
developed and is generally governed by the building
height/design and boiler room location. Chimney inside
diameter determines the restriction to flow with the larger
diameter having less restriction. Generally, the inside
diameter should never be smaller than the diameter of
the breeching connecting into it.
Figure A5 shows minimum chimney sizes for Multi-Temp
power gas heating plants. (Sizes based on first module
located 6" from chimney and proper breeching size, as
determined from Appendix A. If first module is located
more than 6" from chimney or breeching is non-standard
configuration, then proper chimney height and diameter,
for a specific heating plant Btuh input capacity & breech-
ing, can be determined from ASHRAE guidelines.)
SECTION A
194 sq. in.
15" x 13"
SECTION B
124 sq. ft.
12" x 11"
MG-2310 HEATING PLANT
15
"
11
"
FIGURE A4
Boiler
Model
Rectangular
Linear x Ht.
(In. x In. x Ft.)
13 x 18 x 22
18 x 18 x 23
20 x 20 x 25
20 x 24 x 25
24 x 24 x 25
Circular
Dia. x Ht.
(In. x Ft.)
14 x 22
16 x 23
18 x 25
20 x 25
22 x 25
CHIMNEY SIZING (MINIMUM)
MG-770
MG-1155
MG-1540
MG-1925
MG-2310
FIGURE A5
