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SECTION C: Installation
21
Venting
CAUTION: Proper installation of flue venting is criti-
cal for the safe and efficient operation of the heater.
General
Appliance Categories
Heaters are divided into four categories based on the
pressure produced in the exhaust and the likelihood of
condensate production in the vent.
Category I – A heater which operates with a non-
positive vent static pressure and with a vent gas tem-
perature that avoids excessive condensate production in
the vent.
Category II – A heater which operates with a non-
positive vent static pressure and with a vent gas tem-
perature that may cause excessive condensate
production in the vent.
Category III – A heater which operates with a positive
vent pressure and with a vent gas temperature that
avoids excessive condensate production in the vent.
Category IV – A heater which operates with a positive
vent pressure and with a vent gas temperature that may
cause excessive condensate production in the vent.
See Table J for appliance category requirements.
Note: For additional information on appliance catego-
rization, see appropriate ANSI Z21 Standard and the
NFGC (U.S.), or B149.1 (Canada), or applicable provi-
sions of local building codes.
CAUTION: Condensate drains for the vent piping are
required for installations of the MVB. Follow vent
manufacturer instructions for installation and location
of condensate drains in the vent. Condensate drain
must be primed with water to prevent gas flue leak and
must be routed to an appropriate container for neutrali-
zation before disposal, as required by local codes.
WARNING: Contact the manufacturer of the vent
material if there is any question about the appliance
categorization and suitability of a vent material for
application on a Category IV vent system. Using im-
proper venting materials can result in personal injury,
death or property damage.
Use only the special gas vent pipes listed for use with
Category IV gas burning heaters, such as the AL29-4C
stainless steel vents offered by Heat Fab Inc. (800-772-
0739), Protech System, Inc. (800-766-3473) or Z-Flex
(800-654-5600). Pipe joints must be positively sealed.
Follow the vent manufacturer’s installation instructions
carefully.
Support of Vent Stack
The weight of the vent stack or chimney must not rest
on the heater vent connection. Support must be pro-
vided in compliance with applicable codes. The vent
should also be installed to maintain proper clearances
from combustible materials.
Use insulated vent pipe spacers where the vent passes
through combustible roofs and walls.
Combustion
Air Supply
Exhaust
Configuration
Heater Venting
Category
Certified
Materials
Combustion Air
Inlet Material
Vertical
Venting
From Inside Building
(Non-Direct Venting)
Horizontal Through-
the-Wall Venting
Vertical
Venting
From Outside Building
(Direct Venting)
Horizontal Through-
the-Wall Venting
IV
Stainless Steel
AL29-4C
Galvanized Steel
PVC
ABS
CPVC
Table J: Venting Category Requirements