CAN I USE MY CHIMNEY WITH MY NEW FURNACE?
Q: Can I use my chimney with my new furnace?
A: The answer is a definite maybe. Or more likely, maybe not. Truth
is, furnace technology has advanced significantly in recent years.
The higher efficiencies and enhanced performance achieved by today's
furnaces make specific demands many existing masonry chimneys simply
can't meet. Your local independent Goodman dealer can offer the best
advice on how to configure your new furnace to get the most comfort
for years to come.
SIZE CAN BE AN ISSUE
There are several reasons why new furnaces and existing masonry
chimneys aren't compatible. One area of concern for an HVAC contractor
might be the size of the chimney. Modern, higher efficiency furnaces
transfer more heat into your home and less heat up the chimney than
older, less-efficient units. That's great news because it means
you're getting more for your energy dollar. But it also means your
existing chimney might now be too large for the new furnace, preventing
proper venting of flue products and causing condensation problems
inside the chimney.
In addition, today's induced draft furnaces often require an additional
natural draft appliance (such as a gas water heater) be installed
into the same chimney for proper venting. Relining the masonry chimney
with a metal vent can eliminate this requirement. Other areas for
furnace-chimney incompatibility could include the absence of a tile
liner in the chimney and the location of the chimney on an outside
wall of the home.
IT IS POSSIBLE TO MIX OLD AND NEW
There are installations where it is possible to marry a new furnace
to an existing chimney. Chimney height and location are key factors,
as are proper lining and physical condition of the chimney. Building
codes also must be taken into consideration. These requirements
must be met to ensure proper draft in the chimney for adequate venting.
WHY IS CONDENSATION A PROBLEM?
An older less efficient furnace produced a higher volume of flue
gas carrying more water vapor, a natural product of combustion,
up and out of the chimney. Flue gas from today's higher efficiency
furnaces contain less dilution air from inside the home which can
increase the risk of condensation. This means the chimney is cooler
and water vapor will condense on the inside walls of a cold chimney,
just the reverse of taking a glass of ice water outside on a hot
summer day. Water drops condense on the glass and run off quickly
forming a puddle under the glass. The problem is greatly magnified
in the inside of the chimney due to its' size.
Condensate in your chimney is the source of two major problems.
The water combines with flue gases and forms corrosive acids which
eat away at the chimney deteriorating tiles, bricks and mortar.
Secondly, in winter conditions, moisture freezes and thaws breaking
away mortar and bricks. This can not only quickly destroy a chimney
and create leaks into the house, but moisture can damage interior
drywall near the chimney as well as running back into the furnace
causing corrosion there too.
UNLINED VERSUS TILE-LINED CHIMNEYS
The difference between an unlined masonry chimney and one lined
with tile is simple but significant. An unlined masonry chimney
is constructed only of brick and mortar. A tile-lined chimney has
the same brick-and-mortar exterior appearance but it also uses rectangular
or round fired clay tile pipe in the center. An air space separates
the liner from the brick exterior. If you have an unlined masonry
chimney, a listed metal liner kit should be installed by a reputable
HVAC contractor. All new masonry chimneys are built with a clay
tile liner, but in some cases even a tile lined chimney can't be
used to vent some new furnaces. So call your local independent Goodman
Dealer for more information on matching a new furnace with an existing
chimney. That way, when it comes time to make a decision on a new,
efficient Goodman furnace, you'll be warmed with all the facts and
the right information!
© Copyright Goodman Industries Inc., 1999
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