Application Note

2 Fluke Corporation Carbon monoxide: A mechanic’s approach
Notice chimneys, vertical
vents, sidewall vents, air intakes
and exhausts, exhausts that
could become intakes (such as
drier vents that stick open from
lint build-up), building penetra-
tions proximity to doors and
windows, and meter locations.
Look underneath decks and
porches, at the garage location,
inside corners for vents, and
notice shrubberies and trees,
prevailing wind direction and
possible effects, and foundation
type (slab, crawlspace, base-
ment). Look in window wells
and crawlspace access wells,
and just generally notice things.
Later, as you focus on indi-
vidual components such as the
furnace or boiler, water heater,
venting and ventilation, you
will return to the outdoors to
pay more attention to the details
and interactions of functions.
You might be surprised by how
a seemingly unrelated outdoor
feature can affect the indoor
function of a process.
Check more than just CO
Before you leave the outdoors,
record the outdoor ambient CO
2
so you can compare it to indoor
levels. Outdoor levels could be
as low as 380 ppm CO
2
or less
in rural and seacoast loca-
tions, or above 500 ppm CO
2
in
congested urban locations. Then,
as you start your indoor survey,
record CO
2
ppm, CO ppm and
humidity on your air meter.
LEED-EB IEQ2
(1)
Credit 1 CO
2
concentrations can range from
less than 1,000 ppm CO
2
to over
2,000 ppm CO
2
depending on
per person ventilation require-
ments and Met (metabolic) rate
activity levels.
(2)
Elevated CO
2
(from respiration) can be an
indicator of a poorly ventilated
structure, but unvented (spill-
ing) combustion products will
elevate CO
2
and humidity levels
in the occupied space as well.
Increased CO
2
levels in kitchens
may be due to decomposing
organic material (garbage).
CO
2
and water (vapor) are
produced in the complete com-
bustion of fossil fuels, and CO
and water (vapor) are produced
from incomplete combustion. A
furnace, boiler or water heater
typically produce 80,000 ppm
to 30,000 ppm (8 % to 13 %)
CO
2
depending on fuel type,
and about a gallon of water per
100,000 Btu input. If a category
I vent is spilling combus-
tion products, the first change
an occupant may notice is
increased condensation on win-
dows due to elevated humidity
that hadn’t occurred previously.
The first rule of fire
Fire must be safely confined
and controlled while maintain-
ing correct fuel supply, oxygen
supply, and ignition temperature.
When we build a fire indoors,
we must know that the combus-
tion products will vent to the
outdoors. Appliances designed
to operate over extended periods
of time like a furnace, boiler or
water heater must be vented
directly to the outdoors. Products
with limited operating times
such as residential stoves, ovens
and space heaters are usually
expected to have products of
combustion in quantities low
enough to be vented by normal
building ventilation, which
may be relying entirely on the
natural infiltration of air through
structural leaks. As oxygen is
consumed and vent products
exit the building, fresh air from
outdoors must be continuously
supplied or disaster will follow.
Combustion analysis
Warm up and zero your com-
bustion analyzer outdoors.
Combustion products must be
sampled undiluted before any
draft hoods, barometric draft
dampers, or any dilution air
injection. (Some high effi-
ciency direct vent boilers may
draw air from the air intake
into the combustion air blower
prior to the exhaust pipe.)
Sample the O
2
and CO on
startup and monitor as the
process settles in to steady
state operation. CO may be
high on startup and reduce to
Once inside the structure, consider yourself as a combination of
police detective and crime scene investigator.
Here are some questions to ask:
What kind of CO alarm sounded?
When did the alarm sound?
Was it a standard CO detector
designed according to UL 2034 that
specifies that alarm must sound
within 1 to 4 hours at 70 ppm CO, or
do they have a low level alarm model
that sounds after 5 minutes when CO
reaches 15 ppm to 34 ppm?
Can you retrieve the maximum CO
level retained in the alarm memory?
What CO level did the firemen find?
What other comments did the fire-
men have besides suggesting to call
the heating contractor?
Did the alarm sound during early
morning hours when all were asleep
indicating possible ventilation and
venting problems?
Did any of the occupants exhibit any
physical symptoms?
Did it sound after everyone was
awake indicating a possible occu-
pant created condition from space
heaters or automobile warm up in an
attached garage?
Did it sound on Sunday afternoon
when friends or relatives came for
dinner?
Did they burn the roast, burn the
biscuits, or burn the food in the pan
on a burner they forgot about?
Is there an exhaust fan in the kitchen
over the stove and is it used?
Was an outdoor cooking grill used
and at what location?
What about gasoline powered tools
and equipment?
Is smoking allowed indoors?
Did it sound shortly after everyone
retired for the night and was the
fireplace used on that night?
Questions to ask