CLEAN BURN CB 140, Operator'S Manual

Page: 81 / 142

Operator's Manual: Models CB-1750, CB-2500 & CB-3250
8-1
SECTION 8: ADJUSTING THE DRAFT OVERFIRE
Checking for Correct Draft Overfire
WARNING:
Correct draft overfire is
essential for the proper and safe operation
of your furnace.
Your furnace is equipped with an observation/
draft reading port to check draft overfire.
A
qualified serviceman with proper equipment
must check/adjust your furnace for proper draft.
Contact your Clean Burn dealer for this service.
1. Insert the probe of the draft gauge
instrument into the draft reading port in
the observation port as shown in
Figure 8A.
NOTE: Follow the directions with the
draft gauge to use your specific type of
gauge.
2. Note the draft overfire reading on the draft
gauge.
ATTENTION: The draft reading should
be in the -.02 to -.04 w.c. range. Poor
draft (i.e. -.01 to +.08) results in back
pressure in the furnace and poor burner
performance. Too much draft overfire
(i.e. greater than -.04) sucks the heat from
the furnace and results in abnormally high
stack temperature.
Figure 8A - Checking for Proper
Draft Overfire
Understanding the Importance of Draft
Draft in the furnace is created as the hot combustion gases rise up the stack, creating a negative pressure
inside the stack and the furnace. This negative pressure is measured as inches of water column (W.C.) of
draft. A proper draft overfire of -.02 to -.04 w.c. is essential so that all combustion products travel away
from the burner, down the combustion chamber, through the furnace flues and up the stack.
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