CA-3
I’ve always just eyeballed the flame. Is it
really important to do combustion testing?
Looking at the flame color, shape and stability
has been used as a “rule of thumb” for many
years but eyeballing will not allow you to opti-
mize the efficiency, safety, or environmental
compliance of your equipment. Just as doctors
make use of the most sophisticated instrumen-
tation possible when diagnosing their patients,
the best way to make sure that your equipment
is operating safely, and at maximum efficiency,
is by using combustion instrumentation.
CA-4
A re traditional instruments just as
good as continuous sampling electronic
instruments?
Traditional instruments will give you information
that is comparable in accuracy to electronic
instrumentation, but electronic instruments
have several advantages that can be very
important.
For example, many electronic instruments
monitor on a continuous basis, like a movie or
video camera. Traditional instruments are more
like a still camera that takes only one picture at a time.
With traditional instrumentation (the still camera), you
might miss the most important picture because your
camera is only capable of taking one picture at a time.
Because most electronic instruments sample on a con-
tinuous basis, like a video camera, you can see all the
information that will help you to evaluate the operating
condition of your equipment.
Electronic instruments will also do sampling and effi-
ciency calculations rapidly and automatically. Some
models will print out complete reports of test results or
transfer the stored data to a computer while adding
time and date information of the data collected.
CA-5
What do I have to do to measure for combus-
tion efficiency?
You only need to measure gas concentration
(oxygen or carbon dioxide) and temperature to
determine combustion efficiency.
Although other gases (NO
X
, CO, SO
2
) do not
significantly effect combustion eff
i c i e n c y,
these gases are an important safety and envi-
ronmental concern.
CA-6 Where should I take my sample?
The measurement for gases and temperature
should be taken at the same point. Make sure
that the sample point is before any draft
diverters and barometric damper so the gases are
not diluted and the temperature has not been
decreased by outside air. A proper sampling
location for a residential gas furn
a c e
would be inside the heat exchanger tubes.
For residential and light commercial or
industrial equipment, use the following
guidelines:
Oil Burners - Locate the sampling hole at least six
inches upstream from the furnace side of the draft reg-
ulator and as close to the furnace breaching as possible.
Gas Burners - Locate the sampling hole at least six inch-
es upstream from the furnace side of the draft diverter
or hood, and as close to the furnace breaching as pos-
sible.
For Larger Equipment - Locate the sampling point
downstream from, and as close as is practically possible
to, the last heat exchange device (economizer, recuper-
ator, or similar device). This will insure that the net tem-
perature will provide an accurate indication of the effec-
tiveness of the exchangers.
2
Chart 1
CO M B U S T I ON P R O C E S S E S A N D T HE I R C O M B U ST I O N E F F I CI E N C Y R AN G E S
P ro c e s s
Ty pi ca l C omb u st io n
E ffi c ie nc y Ra nge
Home Fire p l a c e
1 0 - 3 0 %
Space Heater
5 0 - 8 2 %
C o m m e rcial Gas Boiler
7 0 - 8 2 %
Residential Gas Furnace with Atmospheric Burner “low eff i c i e n c y ”
7 0 - 8 2 %
Oil Burner Heating System
7 3 - 8 5 %
Induced Draft Furnace “Medium Eff i c i e n c y ”
7 4 - 8 2 %
Boiler with Gas Powered Burn e r
7 5 - 8 3 %
Condensing Furnace (gas & oil) “High Eff i c i e n c y ”
8 5 - 9 3 %
