Installer’s Guide
16
To prevent condensation, it is necessary that the
internal chimney wall temperature always be kept
above the dew point. If the chimney is a masonry
type, it may have to be fitted with a flue liner, when
the temperature loss is too great for the furnace.
If the chimney is a metal type, then an “all fuel”
chimney must be used, such as a Class “A” triple wall
or insulated metal chimney. A liner will act as an
insulator and reduce the stack gas temperature loss.
Insulation may be added around the liner for further
temperature stability. If the chimney is on the home’s
exterior or passes through a sizable, unheated area
of the building, such as a porch, high ceiling attic,
etc., and condensing occurs, the chimney must be
insulated around its exterior to help the flue hold its
temperature. Also, check to see if the chimney is too
large for the furnace and other appliances connected
to it. If so, reduce to proper size (see Appendix E of
NFPA31) by lining. Be sure to use stainless steel
liners, such as stainless types 430, 304, or for the
toughest corrosion problems, type 316. If the chimney
is the correct size for the unit and condensing still
occurs, then insulating the vent connector and/or
reducing the efficiency of the furnace may have to be
done to raise the chimney temperature.
More detailed information may be obtained from the
latest edition of the ASHRAE HVAC Systems and
Equipment Handbook.
Should the previous recommendations and the
information obtained from the ASHRAE Handbook fail
to resolve a condensation problem, another alternative
to consider is power side wall venting.
DRAFT REGULATOR
A barometric-type, draft regulator is supplied with the
furnace. Installation or operating conditions that pro-
duce excess amounts of draft can reduce the heating
efficiency of the furnace. The purpose of the regulator
is to adjust and control the flow of flue gases from the
furnace by stabilizing the amount of chimney draft to
which the furnace is subjected.
Generally, install the barometric draft regulator in the
vent connector as close as possible to the flue outlet col-
lar of the furnace. However, always refer to the draft
regulator manufacturer’s installation instructions for
application specific recommendations.
POWER (SIDE-WALL) VENTING
The manufacturer will NOT assume responsibility for
damage to, and deterioration of, exterior building ma-
terials, e.g. brick, siding, clapboards, and etc., in close
proximity to the vent terminal due to operation of a
power vented, oil furnace. This policy is applicable re-
gardless of the cause of sooting.
PREVENTION OF CHIMNEY CONDENSING:
F
:$51,1*
PROPER VENTING REQUIRED!
Improper venting may lead to condensation in the
chimney. This may result in property damage, injury, or
loss of life. To prevent condensation refer to NFPA 31
Section 6 and Appendix E.
Stack gas may do one of two things as it escapes up the
chimney:
A. Remain entirely in a gaseous state if the internal
chimney wall temperature is above the dew point, or
B. Condense water vapor on the chimney walls if they
are chilled below the dew point.
Condensing will always occur on chimney walls
whose temperatures are below the dew point, but the
condensate may evaporate when the walls warm above
the dew point. If the chimney wall temperature does
not exceed the dew point during the heating cycle of
the furnace, the moisture may accumulate in large
enough quantities to cause problems such as corrosion
of a metal chimney (especially plain steel or galvanized
steel), erosion and break up of a tile liner in a masonry
chimney and, in severe cases, corrosion of the heat
exchanger. Condensate also could enter the home
through cracks or joints in the chimney in a worse case
situation.
Condensation most likely will not occur at the bottom
of the chimney because the stack gas heats the
chimney walls as it rises and the bottom will be heated
first. This heating of the walls will cause the stack
gas temperature to drop, which in turn may reduce
the stack gas temperature below dew point, causing
condensation to appear on the upper part of the
chimney first. This condensation may then run down
inside the chimney and drip back as far as the flue pipe
and heat exchanger, where corrosion may occur, if not
treated.
