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INSPECTION OF THE DUCT SYSTEM
You probably wonder how you can know if your
system is losing large amounts of energy. Although it is often
difficult to be sure without testing, some tell-tale signs,
if present in your duct system, should make you have it checked
by a professional.
It will help to make a simple diagram of the system. This
can be a rough sketch. There is no need for blueprint quality
here.
The first thing you need to do is find the central heating
unit. That should be no problem if it is located in a basement.
It is probably something you pass by almost every day. However,
it may be located in an attic or crawl space.
Safety Tips
To get near the ducts, you may have to look into spaces you
have never been in before, especially if the duct system is
located in an attic or crawl space. Therefore, be sure to
follow common-sense safety rules:
- Guard against falls, cuts, and other personal injuries.
- Do not open up or probe into any electrical devices, wires,
or connections.
- Wear an approved mask if you go into an area with fiberglass
or loose fill insulation.
- Before you touch any un insulated duct, hold your hand
about an inch from it to check if it is hot. This is especially
important in furnaces fueled with gas or oil, because the
vent pipe that carries the flue gases to the chimney looks
like a small duct yet may have a temperature of several hundred degrees Fahrenheit. Generally the vent will be
a round sheet-metal pipe about six inches in diameter that
leads upward from the furnace cabinet. (If the furnace is
one of the new high efficiency models, it might be vented
horizontally.)
Filters
While you are at it, you might want to locate the filter,
which is usually within the central fan unit or at the return
register. The filter removes dust and other small particles
that otherwise could interfere with the operation of the blower
and the furnace heat exchanger. When it fills up with dust,
it cannot do its job and needs to be changed.
Experts recommend that the filter be changed several times
during each heating season. At about a dollar each, frequent
filter changes are a low-cost way to save energy, protect
your heating equipment, and remove some of the dust that otherwise
would be delivered to the living space.
How to Distinguish Between Supply and Return Ducts
Once you have found your central heating equipment, you will
notice ducts leading away from it. There is a supply duct
and a return duct, but which is which? In one common type
of installation, the return duct leads down from the basement
ceiling to enter the furnace near the floor. The supply duct
runs out from the top of the furnace. There are
many types of installations and it is not always easy to tell
which is the supply and which is the return just by looking
at the ducts, particularly if you are not familiar with them.
You can wait until the furnace comes on, or the thermostat
can be pushed up for a short while to force the furnace to
come on. If the ducts are made of sheet metal, you should
be able to feel the supply ducts getting warm. The returns
will not change much in temperature. Another possibility is
to follow what you think are the supply ducts to one of the
registers. If this is in fact the supply side, you should
be able to feel air coming out of the register.
How to Identify Trunks and Branch Ducts
After you have identified the supply and return sides of
the duct system, you can follow the supply side. A long, boxlike structure called a trunk which sprouts
smaller branch ducts that lead out toward the rooms of the
home. Another common installation has all the supply ducts
branching directly from the furnace like the arms of an octopus.
Building Spaces Used as Ducts
So far we have assumed that the duct system is completely
separate from the other components of the home. Often this
is not so. To save money, builders sometimes use the building
structure itself as part of the duct system. One common tactic
is to use the spaces between basement or ceiling joists as
ducts. (Joists are the horizontal-running boards—generally
2” x 10” or 2” x 12”—that support the floor above.)
Although this type of construction can be made to operate
efficiently, it often leads to significant energy losses.
One reason is that joist-space ducts are likely to be un-insulated.
Another problem is that they may have unintended leakage paths
to the outside, typically through the end of the joist cavity.
With returns, it is even more common to see portions of the
building structure used as part of the duct system. Some homes
have no return at all; the furnace simply has an intake grille
through which basement air is drawn in to be warmed and distributed
to the home.
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