Frontier Gas Heat – PN 10-2027 – June 2018 25
The AIR-FREE METHOD of MEASURING CO
Air-free measurement of CO takes account of the amount of excess air by incorporating an adjustment to the as-
measured ppm value, thus simulating air-free (oxygen-free) conditions in the combustion gases. To do this, a reading of
oxygen (O2) or carbon dioxide (CO2) percentage is taken from the combustion gases along with the as-measured CO
reading. This can be done with a meter having the capability of measuring CO
and O2 or CO2 percentage, or it can be
done with two different meters, one measuring CO ppm and one measuring O2 or CO2 percentage.
If air-free CO is determined with a single meter, an integral electronic chip calculates the air-free level from as-
measured CO ppm and O2 percentage.
If two meters are used, the equations below can be used to determine the air-free level of CO in a combustion gas
sample.
For natural gas or LPG, using as-measured CO ppm
and O2 percentage:
CO AFppm = 20.9 x CO ppm
20.9-O2
For LPG, using measured CO ppm and CO
2 percentage:
.
CO AFppm = 14 x CO ppm
CO2
For natural gas, using measured CO ppm and CO2 percentage:
CO Afppm = 12.2 x CO ppm
CO2
Where:
CO AFppm = Carbon monoxide, air-free ppm
CO ppm = As-measured combustion gas carbon monoxide
ppm
O2 = Percentage of oxygen in combustion gas, as a
percentage
CO2 = Percentage of carbon dioxide in combustion gas, as a
percentage.
GAS BURNER OPERATION
NOTICE: For reliable operation, set Air-Fuel mixture conservatively based on installation conditions. Carbon
dioxide, Oxygen, and Carbon Monoxide readings should be taken through 1/4" test port in front jacket opening just to right
of burner (see FIG. 5A). Sample tube must extend at least six (6) inches into front cover to obtain accurate readings. A test
port is provided for the flue box (see FIG. 5A) to measure draft loss.
NOTICE: For accurate efficiency calculations, measure flue gas temperature in flue pipe at flue outlet. Flue box and
over fire temperatures may be higher than flue gas temperature measured in the flue pipe.
Note: When Air Box is used, CO
2
/O
2
must be checked with air box cover in place.
AFTER 15 MINUTES RUNNING, CHECK AND RECORD:
1. DRAFT AT OVER FIRE/CHIMNEY ………………………… -0.02” to –0.12” w.c.
2. DRAFT AT OVER FIRE/POWER VENT…………………….. -0.10" to –0.12” w.c.
1. CO
2
LP Gas………………………………………………………… 9.7 Min / 10.7 Max
Natural Gas…………………………………………………… 8.6 Min / 9.2 Max
2. O
2
LP Gas………………………………………………………… 4.5 Min / 6.0 Max
Natural Gas…………………………………………………… 4.5 Min / 5.5 Max
6. STACK TEMPERATURE …………………………………… 350
o
to 450
o
F
7. CO TEST………………………………………………………… Must be less than 400 ppm
air-free
Draft over fire with a chimney should be -0.02” to –0.12” w.c.
If not, recheck chimney, chimney base and flue pipe for blockage or clean out door openings.
Draft over fire with a power vent (sidewall vent) should be -0.10" to -0.12" w.c.
If not, adjust power vent damper, check power vent fan is turning, or vent blockage.
To Next Page
Loading...
Need help?
General
