Specifications

19
4.1. Gravity Systems
4.1.1 The chimney
Chimneys come in different types, shapes and sizes.
The two main types of chimneys are: metal and
masonry.
Metal chimneys are available in different types of
metal, including 430, 304, 316 or AL29-4C stainless
steel, or it could be in aluminum. Metal chimneys
are also called “pre-fabricated”, “Class A”, “Type B”
as well as “single-wall”, “double-wall”, “triple-wall” or
“zero-clearance”. Although they all serve the same
purpose - to remove products of combustion and
maintain proper draft – each type has limitations in
the application in which it can be applied.
A “pre-fabricated” chimney is a chimney that is
made as a standard product using a standardized
manufacturing method and is made with a joint-
system that makes it easy to install in the eld.
Virtually all metal chimneys are “pre-fabricated”. One
exception, however, is the welded single-wall steel
pipe which is typically designed and assembled via
welding in the eld.
The table below shows each chimneys application
and listing:
Metal chimneys are available in many sizes, some
from 4 inch ID all the way up to 60 inch ID. Sizes
up to 12 inch ID are often considered “residential”
sizes while sizes larger than 12 inch are considered
“commercial”. The size of a chimney affects its
capacity and how much product of combustion it can
remove. Each size has a specic usable area, which
is called the “effective area”. This area, along with the
chimney height, determines the chimney’s capacity.
It is important to understand that the cross-sectional
area grows exponentially as the ID increases. For
example, a 6 inch ID chimney has a cross-sectional
area of approx. 28 sq.in, while an 8 inch ID chimney
has a cross-sectional area of approx. 50 sq.in.
Increasing the ID by 33%, the cross-sectional area
increased by almost 80% - and so did the chimney’s
capacity. Increasing the ID from 6” to 12” (100%
increase) increases the cross-sectional area by
400%!
Masonry chimneys are normally built using brick and
mortar. The products of combustion are conveyed
through a ue or liner in the center of the chimney.
This ue or liner can be square, rectangular, oval or
round.
Just as steel chimneys, a masonry chimney has an
effective area. Only a certain area of a ue is used
due to general airow patterns or characteristics.
4. Venting System Design
Uses Gas Appliance
Vent
Chimney Liner Building Heating Appliance
Chimney
Pellet Vent Special Gas
Vent
Fuel
Nat. Gas, Propane
and LP only
Nat. Gas, Propane
and LP only
Nat. Gas, Propane,
LP, Oil, Solid Fuel
Nat. Gas, Propane,
LP, Oil, Solid Fuel
Nat. Gas, Propane,
LP, Oil, Solid Fuel
Pellets, Nat. Gas,
Propane, LP
and Oil
Nat. Gas, Propane,
LP and Oil
Test Standard
UL441 UL1777 UL103 UL103 UL103 UL641 UL1738
Max. Operat-
ing Tempera-
ture
400°F above
ambient
400°F above
ambient
1000°F
1400°F 1 Hour
2100°F 10 Min.
1000°F
1400°F 1 Hour
2100°F 10 Min. *)
1000°F
1400°F 1 Hour
2100°F 10 Min.
500°F above
ambient
Single Wall: 480°F
Double Wall: 550°F
Operating
Conditions
Gravity or induced
ow, neutral and
negative pressure
Gravity or induced
ow, neutral and
negative pressure
Gravity or induced
ow, neutral and
negative pressure
Gravity or induced
ow, neutral and
negative pressure
Gravity or induced
ow, neutral, nega-
tive and positive
pressure
Gravity or induced
ow, neutral and
negative pressure
Gravity or induced
ow, neutral and
negative pressure
Appliances
Listed gas appli-
ances and other
appliances listed
for venting with
Type B gas vent
Listed gas appli-
ances and other
appliances listed
for venting with
Type B gas vent
Listed building
heating appliances
including replaces
and stoves
Listed building
heating appliances
including replaces
and stoves
Listed building
heating appliances
including replaces
and stoves
Pellet fueled and
certain gas, or oil
appliances
Listed gas or oil
red building heat-
ing appliances and
other
Material:
- inner
- outer
Aluminium
Aluminum/galv.
steel
Aluminum
N/A
Stainless steel 304/430 SS
430 or Galv. Steel
304/316 SS
Alumnized steel
430 SS
Alumnized steel
AL29-4C
Alumnized steel
Codes &
Standards
NFPA54, NFPA211 NFPA54, NFPA211 NFPA37, NFPA54,
NFPA211
NFPA37, NFPA54,
NFPA211
NFPA37, NFPA54,
NFPA211
NFPA211 NFPA37, NFPA54,
Mechanical
Draft System
Location
Termination only Termination only Termination only Termination only Termination or
in-line
Termination only Termination or
in-line