Application Note

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Application Note

F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y

Carbon monoxide:

A mechanic’s approach

It’s not always technical maid ser-

vice. Sometimes HVAC professionals

are rewarded with a mystery and

given the opportunity to put our

technical detective skills to work.

How accurately we solve combustion

related mysteries is directly related

to our fundamental understanding

of the science and technologies in

effect, our choice of tools and test

equipment, our previous experi-

ences, and even our imagination.

The answers lie beyond

the obvious

Carbon monoxide consumer

awareness is still on the

increase. More and more

consumers are installing CO

detectors in their homes and

workplaces. This is good. It

offers occupants a level of safety

they did not have previously,

and offers the expert (you) an

opportunity for in-depth site

analysis.

So how does it usually unfold?

An occupant calls the fire

department after a CO alarm.

The firemen may not see an

obvious source of the CO, so they

recommend having the furnace

(or boiler) checked by a heat-

ing contractor: the combustion

expert. It’s your job to find the

source of the CO under current

conditions, or to try to duplicate

variable conditions under which

CO could be produced. This is a

tall order, requiring a process of

elimination of possible malfunc-

tions and a keen awareness

of variables, such as building

depressurization and gasses (air

and vent products), that could

behave unexpectedly.

While you’re driving to the

jobsite, turn off the radio and

think about the abundant pos-

sibilities. Think of the structure

in its entirety as a system.

Combustion appliances are only

a part of the integrated whole.

What else is competing for or

interfering with combustion air,

fuel supply, vent function? How

can contaminants such as chlo-

rides, sulfides, VOC’s, dust, and

dirt affect component integrity

and operation?

Think about some of the

questionable creative engineer-

ing you’ve seen from end users

trying to save on energy costs.

Think about all of the different

fossil fuel appliances and prod-

ucts, wood fireplaces and stoves

that may be in play: some fixed,

some portable, some that drive

away. Think abo ut what could

be external to the structure

that could produce combustion

products and be drawn into the

occupied space: idling school

buses or trucks, standby gen-

erators in exercise mode, poorly

placed or improperly installed

vent terminations.

The list of possibilities is

seemingly endless, and more

often than not, it’s two or more

processes gone wrong. One

process may have been operat-

ing on the edge of acceptability

since day one, and a second

process changes enough to

throw the first process over the

edge. Every job is different and

valuable lessons can be learned

from each. Be observant and

allow your mind to explore the

possible system failure modes

and their interacting effects.

Exterior survey

When you arrive at the job-

site, observe the exterior of the

system (the building and its

immediate surroundings). Before

entering the building, turn on

your environmental air meter

(such as Fluke 975) and give it

time to warm up and zero out-

doors. This will give you time

for a walk-around.

Summary of content (6 pages)

PAGE 1
Carbon monoxide: A mechanic’s approach Application Note It’s not always technical maid service. Sometimes HVAC professionals are rewarded with a mystery and given the opportunity to put our technical detective skills to work. How accurately we solve combustion related mysteries is directly related to our fundamental understanding of the science and technologies in effect, our choice of tools and test equipment, our previous experiences, and even our imagination.
PAGE 2
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 penetrations 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, basement).
PAGE 3
normal values as steady state operation is reached. Allow at least 15 minutes for steady state operation to be achieved. • Think about what you are measuring. To find the amount of excess air (air that has not been used in the combustion process), we measure O2 or CO2. To discover the quality of combustion, we measure CO. • Since before any of us started in this trade, the national standard for maximum CO in the vent of vented products has been 400 ppm CO air free.
PAGE 4
What not to rely on: • Don’t use a CO reading at a that creates friction in the venturi, then less than normal primary air will be entrained and a dirty fire will develop that secondary air cannot clean up. - Cold oil from an outdoor tank will cause increased oil flow through an oil nozzle and resists atomization and proper fuel/air mixing. Reduce nozzle size and increase pump pressure to clean up the fire.
PAGE 5
Close doors to the equipment room. Monitor the pressure differential between the equipment room and outdoors. Then open the equipment room door (if it is an interior door) and monitor the pressure differential again. Any indoor depressurization means you need more combustion air. Venting Increasing CO and decreasing O2 (or increasing CO2 ) levels in the vent indicate combustion air problems and possible venting problems. Most of the efforts to ensure adequate combustion air will apply to venting as well.
PAGE 6
Combustion air tips Any return ducts located in the same space as the fossil fuel equipment must be sealed airtight. Filter access panels must be sealed airtight. Returns and filter access panels located in garages must be sealed airtight, airtight, airtight. When combustion air openings to the outdoors are used, always use two: one high, one low. If ducts are used to connect to the outdoors, use two ducts, one for each opening.