Burnham RSA - Manual (Page 18)

8
IV. Venting
A
. General Guidelines.
1. Vent system installation must be in accordance
with these instructions and applicable provisions of
local building codes. Contact local building or fire
officials about restrictions and installation inspection
in your area.
2. The RSA Series is designed to be vented into a
fireclay tile-lined masonry chimney or chimney
constructed from type-L vent or a factory
built chimney that complies with the type HT
requirements of UL103. The chimney or vent pipe
shall have a sufficient draft at all times, to assure
safe proper operation of the boiler. See Figure 11 for
recommended installation.
a. Install a draft regulator (supplied by installer)
following the instructions furnished with the
regulator. See Figure 12 for alternate regulator
locations.
b. With any new or replacement installation the
chimney has to be considered. Chimneys that
have a high heat loss become less suitable as
the heat loss of the home goes down and the
efficiency of the boiler goes up. Most homes
have a chimney appropriate for the fuel and
the era in which the home was built. That may
have been a coal fired or an inefficient oil fired
boiler built into a home without insulation or
storm windows. With increasing fuel prices that
home probably has been insulated and fitted with
storm windows so that the heat loss of the home
has been reduced. This requires less fuel to be
burned and sends less heat up the chimney.
A new boiler probably has a higher efficiency
than the boiler being replaced. That probably
means that the stack temperature from the
new boiler will be lower than that from the
old boiler and with less room air being drawn
up the chimney to dilute the stack gases. The
combination of a large uninsulated chimney,
reduced firing rate, reduced firing time, lower
stack temperature and less dilution air can, in
some cases, contribute to the condensing of small
amounts of water vapor in the chimney. Such
condensation, when it occurs, can cause chimney
deterioration. In extreme cases, the chimney
may have to be lined to insulate the chimney and
thus prevent the condensation. The addition of
dilution air into the chimney may assist in drying
the chimney interior surfaces.
A massive chimney on a cold, or exposed outside
wall may have produced adequate draft when it
was fired with a higher input and greater volumes
of heated gases. With reduced input and volume,
the draft may be severely affected. In one
instance our research showed a new chimney of
adequate sizing produced only -.035” W.C. after
30 minutes of continuous firing at 13.0% CO
2
.
Outside wall chimneys take longer to heat up and
can have .00” W.C. draft at burner start-up. You
may have to consider a special alloy chimney
flue liner with insulation around it and stabilizing
draft cap or even a draft inducing fan in severe
cases.
c. For the same reasons as in (2.) above, heat
extractors mounted into the breeching are not
recommended.
3. For minimum clearances to combustible materials
refer to Figure 2.