Install Instructions

Type B Gas Vent - 3” to 12” Diameter
Installation Instructions
9
Models RHW and RM caps, sizes 3" through 12",
are listed for installation on gas vents terminating
so that the lowest discharge opening shall be no
closer than the minimum height shown i n Table 3
and Figure 20. These minimum heights may be
used, provided that the vent is not less than 8 feet
from any vertical wall. FOR A VENT CLOSER THAN
8 FEET, THE VENT TERMINATION MUST BE
RAISED UNTIL 2 FEET HIGHER THAN THE
STRUCTURE.
Offsets in the attic space should be used to minimize
the amount of vent pipe that must be exposed above
the roof in order to comply with the above. No gas
vent should be terminated less than 5 feet in vertical
height above the highest connected appliance draft
hood outlet.
• If a vent extends more than 5 feet above the roof,
it should be guyed with 3 wires or braced with
2 pieces of rigid conduit
CAUTION
Where heavy snowfall occurs, the cap should
be installed to a height above the average
snow depth.
Figure 19
• A cap or chimney housing offers resistance to the
entrance of rain, snow and debris, as well as birds,
and will minimize the effect of wind on the vent.
It will protect the vent from down drafts caused
by wind.
However, no vent cap, cowl or top can overcome the
adverse effect of a region of high static pressure around
the vent terminal nor the effect of an interior region of low
pressure.
- Reference: American Gas Association Research Bulletin 68
Regions of high static pressure around the vent
terminal can be avoided by following the general
rule for the vent termination given previously. Low
or negative interior pressures in the building may
be caused by (1) failure to provide combustion air,
(2) excessive use of exhaust fans, and (3) tight
construction resulting in the lack of infiltration air.
Vented clothes dryers and fireplaces also will
remove large amounts of air from the interior,
tending to produce a low interior pressure.
WHERE THE VENT PASSES THROUGH THE
ROOF, the roof sheathing should be cut away
sufficiently to PROVIDE A MINIMUM OF 1-INCH
CLEARANCE from the vent pipe. The vent pipe
should be run up to a point where the top end is at
least a foot or so above the roof.
An RF roof flashing should be placed down over
the upper end of the pipe, and adjusted so the base
place of the flashing fits tightly against the roof with
the vent pipe held in a position, MAINTAINING THE
1-INCH CLEARANCE FROM COMBUSTIBLE
CONSTRUCTION. The flashing may be sealed to
the roof. The RS storm collar must be placed
immediately above the roof flashing. The storm
collar must be sealed with roof cement or RTV
silicone to seal the joint between the storm collar
and the vent pipe. The storm collar provides
protection against the entrance of any moisture into
the flashing.
(See Figure 16.)