Owner's Manual

10
COMPLETE COMBUSTION OF NATURAL GAS
FIGURE 1-1
wind effects or pressure areas which may reduce
or impede vent ow. This does not imply that
terminations at these locations will assure proper
venting in every instance. Because winds uctuate
in velocity, direction, and turbulence, and because
these same winds impose varying pressures on the
entire structure, no simple method of analysis or
reduction to practice exists for this complex situation.
Manifold vents may be run horizontally or sloped
upwards toward the common vent. Slope should not
exceed ¼” per foot unless required otherwise by local
codes. Regardless, minimum vent connector rise as
determined for each appliance must be maintained.
Manifold vents may be of constant diameter (Fig. 1-5)
in which case they are of the same size as the common
vent or its equivalent. Manifolds may also be tapered
(Fig. 1-6) for the actual input to a particular section of
the manifold. Difference in operating characteristics
between properly sized constant diameter manifold
vents or tapered manifold vents are negligible and
choice is usually dictated by convenience and cost.
1.4.4 INDIVIDUAL VENTS – Economics thru the use
of smaller vent pipe and the elimination of ttings
could dictate the use of an individual vent system for
each module (see Fig. 1-7) rather than a combined
vent system. If the individual vents are of the proper
diameter and the total vent height is a minimum of
5 ft., the systems are self venting and more reliable
than a combined vent system since, in the latter, it is
impossible to anticipate all contingencies.
1.4.5 VENT AND CHIMNEY MATERIALS AND
CONSTRUCTION – The materials of construction for
vents and chimneys include single-wall metal, various
multi-wall air and mass insulated types as well as
masonry, which could be precast or site constructed.
In many instances, national or local codes will govern
what type may be used. Where choice is possible,
many advantages can be listed for the UL Listed
double wall metal type B vent:
1) warm up is faster with type B vents than vents
having greater mass
2) type B vents permit closer clearance to
combustible material than single wall metal vents
unless special precautions are taken with the latter
3) type B vents are less prone to condensation and
corrosion than single wall metal vents
4) type B vents are lightweight, easy to handle and
assemble
Manufacturer’s instructions relative to installation
of their product should be followed as long as they
comply with the National Fuel Gas Code and/or local
codes. Some items to consider are:
1) support of lateral runs so that vent pipe does not
sag