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The most common carbon monoxide (CO) problems involve a lack
of oxygen - either because there is simply not enough, or because
the flames cool off before the carbon can join with it. CO is
produced whenever a fuel is burned without enough oxygen on hand.
Carbon atoms in the fuel that normally join up with two oxygen
atoms to form carbon dioxide, which is harmless to human health,
end up with only one oxygen atom and instead form CO.
Basic Steps to Getting CO Into Your Life
It is not enough to understand how to create CO, we need to examine
all of the coordinating factors which can create it and allow
it into the living space.
Five basic factors not only lead to the production of CO, but
will aid in getting it into your homes. Any one major failure
can get CO into your home, but typically three of these factors
must go awry to produce a major problem.
The Flow of Fuel
As you add fuel to a fire, the fire produces more Btus of heat.
It also requires more oxygen to combine with the carbon and hydrogen
to form carbon dioxide and water vapor (H2O. As you continue to
add fuel, the amount of available oxygen needs to keep up or CO
will be produced, which is incompletely burned carbon. In engineered
systems (all modern combustion appliances) the amount of air that
can move through the unit is limited by the design. Any additional
restriction (dirt, lint, carbon) will result in the air flow being
reduced. The air flow is controlled by the laws of nature (hot
air rises). The flow of fuel is controlled by the pressure applied
to the fuel and the size of the hole it is forced through. Any
problem with the pressure of fuel input can lead to problems with
the fuel/air mixture.
Competition for Air
We refer to many kinds of air when describing a standard combustion
appliance (combustion air, primary air, secondary air, dilution
air, return air, supply air, and so on). Air, or more precisely
the oxygen in the air, is fundamental to the combustion process.
The amount of air than can come into standard appliances is typically
controlled by two basic systems. First is the mix of gas and air
before combustion (primary air). This is controlled by the design
of the burner, the pressure of the gas, and any control of the
air stream. The secondary air, or additional air that is needed
to supply oxygen to the flames, is simply controlled by the amount
of air that is drawn through the heat exchanger.
In order for these two simple systems at the appliance to supply
adequate oxygen for complete combustion, there needs to be sufficient
air to the area around the appliance. Any competition for the
air needed for the combustion process can lead to problems. The
power of the competition does not need to be strong to overcome
the natural forces of the combustion appliance.
Venting: The Wild Card
Getting all of the combustion products out of the living space,
a matter of indoor air quality, is fundamental to the safety of
our clients. Codes and venting systems are designed to ensure
this happens. In the cases that combustion appliances are unvented
(they vent into the living space), there are specific directions
for additional ventilation needs (like opening a window).
Venting can be a wild card due to its relationship to both the
weather and the physical configuration, time of year, time of
day, connection with other appliances, connection with the house,
and so on. All of these relationships can have a dramatic effect
on the draft of an appliance. The fundamental principle is that
hot air rises. We can thus figure out how much area in the vent
is needed to get all the combustion products out of the building.
These rules may not always result in successful venting in actual
buildings. Only testing can provide an indication of the operation.
Operation
The operations of the appliance can be broken down into two
components: those defined primarily by the internal controls of
the unit and those dictated by the occupant. We have found many
units where the appliance is not able to operate correctly and
that just happened to keep the unit from being a major liability
to health and safety. Changing any portion of the operation may
affect safety. This includes adjusting the distribution, air tightness
of the unit, ductwork, load/insulation, not to mention touching
the unit itself. The client's operation of the unit can also affect
safety.
Luck (Or Lack of)
Luck is the final card. It is the random combination of the first
four factors and other things that affect the building. Simple
things like unclogging a dryer vent, fixing a bath fan, repairing
ducts, or insulating walls, can change the operating patterns
of the combustion devices.
How it Happens
In addition to the five basic components, we have seen significant
patterns in the creation of CO.
Very few HVAC installers have the equipment necessary to ensure
a safe installation of a combustion appliance is completed. Many
units create CO because of improper setup and testing. Problems
with gas pressure, orifice size, and improper venting are the
most common.
Remodeling
Remodeling a building often involves adding walls and changing
the combustion air location and source availability. At Sun Power
we have seen new house designs which virtually ensure that the
combustion air source will be eliminated. In addition to limiting
the combustion air, remodeling typically increases the pollution
in the area of the combustion devices (for instance installing
a dryer in a small room with the furnace).
Deterioration and Proper Installation
Long-term deterioration of an appliance is not a common factor
leading to CO production. However, deterioration is a common problem
with units that were marginally installed: vents with long horizontal
runs may have just met standards when they were installed but
are prone to rust out over time. Venting into an unlined chimney
can lead to problems (erosion of the chimney can eventually lead
to leaks). Dirt from a crawlspace can fall down and block the
combustion air hoes in a water heater. Even crawlspace furnaces
stay fairly trouble-free unless major contaminants are introduced
into the area. Dryers and water are the chief causes, but rust
and lint are good at blocking everything.
CO can be drastically reduced in the home if the units are installed
correctly in a dedicated area which is not connected to the living
space. This requires a room for the combustion appliances that
is vented with outside combustion air (or sealed combustion units)
and has sealed ductwork.
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