Burnham MEGASTEAM MST288 - Manual (Page 31)

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2. Type B Chimney Connector - a type B chimney
connector can be used to transmit the flue gases
provided flue gas temperature entering the chimney
connector is greater than 310°F.
3. Type L Chimney Connector - a type L vent or
other suitable material shall be used for a chimney
connector if the temperature or exiting temperature
is less than 310°F.
DANGER
Any signs of condensate seepage at the base of
the chimney shall be inspected immediately. The
discoloration may be a sign of chimney damage
and must be remedied immediately.
C. DRAFT
1. The natural draft generated through a chimney is
dependent on several factors including, chimney
height, temperature of flue gases, cross section area
of chimney, chimney wall insulation value, dilution
air and total volume of flue gases, to name a few.
Make sure that the boiler has been running for at
least 5 minutes before measuring the draft.
2. Minimum Draft at Breech (Canopy) – The draft
induced by a chimney must create at least a
pressure of 0 (zero) inches water column (“ w.c.)
at the pressure tapping on the canopy mounted
on rear of boiler (see Figure 17). The pressure
at the canopy cannot be positive since this could
create a condition that allows flue gas by-products
to escape from the draft regulator. A negative
pressure reading up to -.03 inches water column
is acceptable for proper operation. (See Table 8,
Burner Specifications at the rear of this manual for
more details)
3. Minimum Overfire Pressure – The overfire
pressure is another piece of information that is
often measured, however this should be done for
observation purposes only! The breech pressure
must be used to qualify the draft condition. See
Table 8 for more details as a guide. Actual draft and
temperature measurements may be different then
those values in the table.
D. STACk TEMPERATURE
1. The temperature of the flue gases has a significant
effect on the amount of draft created in a vertical
chimney as well as the propensity to create
condensate. The higher the stack temperature, the
greater the amount of draft that can be generated. A
lower stack temperature not only reduces the amount
of draft that can be created but it also increases the
possibility that the flue gases could condense in the
chimney connector or stack.
2. NFPA 31 has information to help the installer
make an appropriate choice of venting materials.
In some cases a chimney may have to be lined to
create sufficient draft. In other cases, the chimney
may have to be lined to prevent the corrosion
of a masonry chimney. Consult with a chimney
specialist knowledgeable on the requirements for
chimney requirements in your area.
CAUTION
Any doubt on the condition of a chimney
or it's ability to prevent the generation and
accumulation of flue gas condensate, must be
relined according to NFPA31.
CAUTION
Use the chimney venting tables as a guide. It
is highly recommended that any borderline
application should result in the relining of the
chimney with a suitable liner that creates sufficient
draft and to protect against corrosion caused by
flue gas condensate.
3. Baffles – The efficiency of the boiler is based on the
insertion of flue baffles supplied with your product.
Under no circumstances are other baffles to be used
on this product. The baffles are installed in the 2 nd
pass (two inner flueways) on the MST396, MST513
and MST629 Refer to Section II, Item E, Paragraph
1 for baffle installation. If there is any doubt
on the application of this boiler on the intended
chimney, consult with your local code officials.
At a minimum, remove the baffles to increase the
stack temperature. See Table 8 for temperature
differential (∆T) with baffles IN and OUT. In
addition, the lower the CO
2
level the higher the
stack temperature.
Figure 1: Smokebox Pressure Tapping for
Checking Draft at Breech