Key Points

  • Carbon monoxide (CO) is produced whenever a fuel burns without sufficient oxygen — carbon atoms that would normally form harmless carbon dioxide (CO₂) instead bond with only one oxygen atom, creating toxic CO.
  • According to the U.S. Centers for Disease Control and Prevention, CO poisoning is responsible for more than 100,000 emergency room visits per year in the United States — and most incidents involve residential combustion appliances like furnaces, water heaters, and boilers.
  • Five factors determine whether CO is produced and whether it enters your living space: the flow of fuel, competition for air, venting effectiveness, appliance operation, and — critically — luck in how these factors combine.
  • Any single major failure in one of these five areas can allow CO into your home — but typically three factors must go wrong simultaneously to create a serious, ongoing problem.
  • In Parker and Douglas County, where homes rely on gas furnaces and boilers for cold-season heating and many are constructed with tight building envelopes that restrict combustion air supply, proper installation, annual maintenance, and CO detector placement are especially important.
  • The most preventable CO production scenarios — improper gas pressure, incorrect orifice sizing, and inadequate venting — are entirely avoidable with professional installation and routine inspection.
  • Contact Parker Heating and Air for professional furnace inspection, combustion safety testing, and heating system service throughout Parker, CO and the surrounding Douglas County area.

Steps to Carbon Monoxide Production

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.

The Five Basic Factors That Bring CO Into Your Home

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.

Factor 1: 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.

What this means for Parker homeowners: Furnace filters are the first line of defense against airflow restriction in this factor. A clogged filter reduces the air available to the combustion process — and in tight Douglas County homes where the furnace runs heavily from October through April, filters can clog faster than the standard 90-day interval. Parker Heating and Air offers furnace filter replacement and furnace maintenance service that includes combustion air assessment alongside standard tune-up tasks.

Factor 2: 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 that can come into standard appliances is typically controlled by two basic systems. First is the mix of gas and air before combustion (primary air) — 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 needed to supply oxygen to the flames, is simply controlled by the amount of air 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.

Common air competition sources in Parker homes: Bath fans, kitchen exhaust fans, dryers, and even whole-house ventilation systems all compete for the same air supply as combustion appliances. In newer Parker and Douglas County construction — where building envelopes are intentionally tight for energy efficiency — this competition is more acute than in older, leakier homes. A furnace or boiler that operated safely before a bath fan was added, a dryer was relocated, or the home was re-weatherstripped may begin to produce CO under the new competition conditions.

Factor 3: 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.

Venting and Parker’s elevation and weather patterns: Parker, CO sits at approximately 5,869 feet above sea level — and altitude affects combustion and venting performance in ways that standard installation guidelines don’t always account for. At higher elevations, air is less dense, which means less oxygen is available per cubic foot of air drawn into the combustion process. This is the same principle that requires pilots to account for density altitude. For Parker homeowners, this means venting systems that might perform adequately at sea level may require adjustment or upsizing at altitude. Annual furnace inspection and combustion testing is the only reliable way to confirm venting is performing safely at Parker’s specific elevation conditions.

Factor 4: 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.

Operation changes that create unexpected CO risk: Many CO incidents in occupied homes follow a seemingly unrelated change — a renovation, a new appliance installation, or even a home energy audit that led to air sealing. What was safe before may not be safe after. Any time a Parker homeowner makes changes that affect the building’s air movement (new weatherstripping, attic insulation, closing off rooms, adding or removing exhaust fans), a combustion safety inspection is warranted. Contact Parker Heating and Air if your home has undergone significant changes since your last furnace inspection.

Factor 5: 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 CO Production Happens in Practice

In addition to the five basic components, there are significant patterns in the creation of CO.

Installation errors: 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. New house designs can 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 Improper 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 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 holes 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.

— Rob deKieffer

What Parker, CO Homeowners Should Do Now

Understanding how CO is produced is the first step — but the practical implication for Parker and Douglas County homeowners is clear: annual professional inspection of all combustion appliances is the most reliable protection available. The combination of Parker’s high altitude, tight modern construction, cold winters requiring heavy furnace use, and the five-factor CO production system described above creates a risk profile that makes routine inspection not just a best practice but a genuine safety priority.

Parker Heating and Air recommends scheduling furnace maintenance before each heating season, ensuring CO detectors are installed on every level of the home and outside each sleeping area, and calling for a professional inspection any time renovations, new appliances, or operational changes affect your home’s air dynamics.

For furnace repair, boiler service, heat pump repair, and combustion safety inspections throughout Parker, CO — contact Parker Heating and Air.

Key Takeaways

Carbon monoxide is produced when fuel burns without sufficient oxygen — a simple chemistry problem with serious consequences. Five factors govern whether CO forms and reaches your living space: fuel flow (filter and pressure), air competition (other exhaust appliances and tight construction), venting (weather, configuration, and altitude all affect draft), appliance operation (any change to the home’s air dynamics can affect safety), and luck (the random combination of the other four). The CDC confirms CO poisoning drives over 100,000 ER visits annually — most involving residential combustion appliances. For Parker and Douglas County homeowners, altitude at approximately 5,869 feet reduces available oxygen per cubic foot of combustion air, making proper installation and annual testing more critical than at lower elevations. The most preventable CO production patterns — improper gas pressure, wrong orifice sizing, and marginal venting — are addressed through professional installation and annual furnace maintenance. Any home renovation, new appliance installation, or air sealing project warrants a follow-up combustion safety inspection. Contact Parker Heating and Air for professional furnace maintenance, inspection, and repair throughout Parker, CO.