3. Boiler Venting & Chimney General
Caution & Warning:
It is advised and recommended that the heating contractor-professional apply vent materials that are approved and agency listed.
Installation of any venting must follow all local codes in conjunction with vent manufacturer instructions and appliance manufacturer
instructions.
All De Dietrich GT series oil-gas fired cast iron boilers are high performance boilers that could operate under all 4 vent
categories as established by ANSI Z21.13/CSA 4.9 Standard. To assist with application where the vent category is
unknown a graph below has been provided to assist you in determining the vent category and what venting materials
would be acceptable. Although the gas vent categories were developed specifically for gas fired appliances, using this
information is helpful for oil fired boilers. It is very important the venting be selected according to the conditions that the
boiler will operate under, minimum and maximum firing conditions of the boiler must be respected. The venting installed
must comply and be certified to all applicable codes and standards for each jurisdiction.
Gas-Vent Category [4] Definitions:
Cat. I
A Boiler, which operates with a non-positive vent (breech) pressure
and flue gas temperatures which avoids excessive condensation
production in the chamber and venting.
Cat. II
A Boiler, which operates with a non-positive vent (breech) pressure
and flue gas temperatures produce condensation production in the
chamber and venting.
Cat. III
A Boiler, which operates with a positive vent (breech) pressure and
flue gas temperatures which avoids excessive condensation
production in the chamber and venting.
Cat. IV
A Boiler, which operates with a positive vent (breech) pressure and
flue gas temperatures produces condensation production in the
chamber and venting.
Chart A
Gas-Fired Appliance Vent Categorization
[According to ANSI Z21.13/CSA 4.9 Gas Boiler Standard]
60
104
148
192
236
280
324
368
412
456
500
Chimney-Vent Pressure
[Inches w.c.]
Ch
im
ney-Ve
nt Fl
ue
G
a
s
Tem
pe
ra
ture °F
(Ne
t, M
in
us
Room
Tem
perat
ure)
15
40
64
89
113
138
162
187
211
236
260
6
7
8
9
10
11
12
11
10
9
8
7
6
Carbon Dioxide [CO
2
] Content %
Ch
im
ney-Ve
nt Fl
ue
G
a
s
Te
mpe
ra
ture °
C
(Net
, Mi
nu
s
R
oom
Tem
perat
ure)
Category I
Typical Vent Types [A,B,C & L]
Category III
Typical Vent Types
[BH, AL294C®, 304-316L SS]
Positive
Negative
Category II
Typical Vent Types
[BH, AL294C®, 304-316L SS]
Category IV
Typical Vent Types
[BH, AL294C®, 304-316L SS]
Chart created by Craig Holdforth
Venting
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