Carbon Monoxide and Your Gas Furnace: Winter Safety Basics for Phoenix Homes

Carbon monoxide, or CO, is a colorless, odorless, poisonous gas. It forms when fuels such as natural gas don't burn completely, according to the U.S. Consumer Product Safety Commission (CPSC). A yearly furnace inspection by a qualified technician and working CO alarms are two protections that both the CDC and the CPSC recommend. Our family-owned team at Viking Heating & Air Conditioning works on gas furnaces in homes across Phoenix and the East Valley.

What Is Carbon Monoxide, and Where Does It Come From?

Carbon monoxide comes from burning fuel. The Centers for Disease Control and Prevention (CDC) says CO is found in fumes produced any time you burn fuel in cars or trucks, small engines, stoves, lanterns, grills, fireplaces, gas ranges, or furnaces. Because you can't see it or smell it, your senses won't tell you it's there. That is the reason CO alarms exist.

None of this means you should be nervous about your furnace. The U.S. Fire Administration explains that CO poisoning can occur when a fuel-burning appliance "such as a furnace, heater or generator, is not working or vented properly." The risk comes from a problem with the equipment or its venting. Catching those problems is what a yearly inspection is for, and working CO alarms add protection.

Other winter CO sources to keep in mind

Your furnace isn't the only fuel-burning item in a home during cold weather. The CDC's prevention tips include never heating your house with a gas oven and never running a car or truck inside a garage attached to the house, even with the garage door open. The CDC also says never to use a generator inside your home or garage, even if doors and windows are open. These are simple habits, and they're worth mentioning to holiday guests who may not know them.

Where Furnace CO Problems Start

A gas furnace burns natural gas to make heat. The U.S. Environmental Protection Agency (EPA) notes that combustion gases can come from "chimneys and flues that are improperly installed or maintained and cracked furnace heat exchangers." The EPA also says that "proper maintenance is important even for new furnaces because they can also corrode and leak combustion gases, including carbon monoxide." That is why the EPA advises having furnaces, flues and chimneys "inspected annually" and says to "properly repair cracks or damaged parts."

The outdoor end of the vent matters too. The U.S. Fire Administration advises making sure vents for the dryer, furnace, stove and fireplace are clear of debris. It's worth glancing at your furnace vent now and then and keeping anything that could block it out of the way.

If you'd like a broader look at how the different home heating systems work, our complete residential heating guide for Phoenix Valley homeowners walks through them in plain terms.

Key Takeaway: The EPA names poorly installed or maintained flues and cracked furnace heat exchangers as sources of combustion gases, so their condition matters for furnace CO safety.

Warning Signs Worth Knowing

One warning sign is a CO alarm. Since CO has no color or smell, an alarm is the tool built to notice it for you. As the CPSC says, never ignore an alarm when it sounds, and follow the steps in the section below.

Your body can also give you clues. The CDC lists the most common symptoms of CO poisoning as headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. The CPSC lists headache, fatigue, shortness of breath, nausea and dizziness as symptoms of low to moderate CO poisoning. It adds that the first symptoms of low to moderate CO poisoning "are similar to the flu (but without the fever)." The CDC also notes that infants, the elderly, and people with chronic heart disease, anemia, or breathing problems are more likely to get sick from CO.

Symptoms aren't a reliable early warning for everyone. The CDC warns that "people who are sleeping, drunk, or under the influence of other substances can die from CO poisoning before they have symptoms." This is one more reason to keep working alarms outside the bedrooms, as the next section explains. If you suspect CO poisoning, the CPSC says to "get outside to fresh air immediately, and then call 911."

The venting can have problems too. According to the CPSC, an inspector should check chimneys and flues for blockages, corrosion, partial and complete disconnections, and loose connections. If you do notice a vent pipe near your furnace that looks loose, disconnected, or badly corroded, it's worth having a professional check it.

Key Takeaway: Never ignore a CO alarm, and if you suspect CO poisoning, get outside to fresh air immediately and then call 911.

Where Should CO Alarms Go, and How Do You Test Them?

If your home has a gas furnace and no CO alarm, our technicians' advice is to get one. Alarm placement follows a simple pattern. Here is what the CPSC and the U.S. Fire Administration recommend:

• Install battery-operated CO alarms or CO alarms with battery backup on every level of the home and outside sleeping areas.
• Place them in a central location outside each separate sleeping area.
• Skip attics and basements unless they include a sleeping area.
• Avoid spots near heating vents or places where furniture or draperies could cover the alarm.
• Choose an alarm that meets the requirements of the current UL 2034 safety standard.

Testing is just as important as placement. The CPSC recommends that you "replace the batteries in their smoke and CO alarms annually and test the alarms monthly." It also points out that pressing the test button "tests whether the circuitry is operating correctly, not the accuracy of the sensor." A monthly test tells you the alarm can sound, which is the part you can check yourself.

An alarm is a backup, not a substitute for a well-kept furnace. In the CPSC's words, "A CO alarm can provide some added protection, but it is no substitute for proper use and upkeep of appliances that can produce CO." The National Fire Protection Association also keeps a carbon monoxide safety page.

Key Takeaway: Put battery-powered or battery-backup CO alarms on every level and outside the sleeping areas, and test them every month.

What to Do If Your CO Alarm Sounds

The CPSC is plain about it: "Never ignore an alarm when it sounds." The CPSC also says not to try to find the source of the CO when the alarm goes off. Instead, follow its steps in order:

1. Immediately move outside to fresh air.
2. Call your emergency services, fire department, or 911.
3. After calling 911, do a head count to check that everyone is accounted for. Do not go back inside until the emergency responders have given you permission.

After the responders have done their work, the next step depends on what they found. The CPSC says that "if the source of the CO is determined to be a malfunctioning appliance, DO NOT operate that appliance until it has been properly serviced by trained personnel." If that appliance is your furnace, leave it off and have a licensed HVAC technician service it before you use it again.

The CPSC adds that if authorities allow you to return to your home and your alarm reactivates within a 24 hour period, you should repeat steps 1, 2 and 3 above and "call a qualified appliance technician to investigate for sources of CO from all fuel burning equipment and appliances, and inspect for proper operation of this equipment."

Key Takeaway: When a CO alarm sounds, don't search for the cause. Get everyone outside to fresh air immediately, call 911, and stay out until emergency responders give you permission.

A Gas Smell Is a Different Emergency

Because carbon monoxide has no smell, a gas odor in your home is a separate warning with its own steps. It's easy to mix the two up in the moment, so it helps to know the difference ahead of time.

The CPSC's instruction is: "If you smell gas or hear gas leaking, leave your home immediately and contact local gas authorities from outside the home." The CPSC also says: "Do not operate any electronics, such as lights or phones, before leaving." A CO alarm calls for leaving and calling 911. A gas smell calls for leaving and calling the gas authorities from outside. In both cases, the first move is to get everyone out of the house.

Why a Yearly Furnace Inspection Matters in the Valley

The safety agencies agree on yearly checkups for gas heating equipment. The CDC says to have your heating system, water heater and any other gas, oil or coal burning appliances serviced by a qualified technician every year. The CPSC agrees. It urges a yearly professional inspection of all fuel-burning home heating systems, including furnaces, boilers, fireplaces, wood stoves, water heaters, chimneys, flues and vents.

When our technicians inspect a gas furnace, we check for cracked or damaged heat exchangers, improper combustion, blocked or damaged venting, failed safety controls, gas leaks, and improper installation or operation. The visit also gives you a chance to ask questions about your alarms while someone is there.

Our post on heating system maintenance for Chandler winters explains what a furnace tune-up usually involves. If your furnace hasn't had its yearly inspection yet, call us and we'll get you on the schedule.

Key Takeaway: The CDC, the CPSC and the EPA all recommend a yearly inspection of fuel-burning heating equipment, which gives a qualified technician the chance to check the venting and the heat exchanger.

Frequently Asked Questions

Can a gas furnace produce carbon monoxide?

It can if something goes wrong. Carbon monoxide forms when fuel such as natural gas does not burn completely. The U.S. Fire Administration explains that CO poisoning can occur when a fuel-burning appliance such as a furnace is not working or vented properly. A yearly inspection by a qualified technician and working CO alarms in your home are two protections that both the CDC and the CPSC recommend.

Where should carbon monoxide alarms go in a home?

The CPSC says to install battery-operated CO alarms or CO alarms with battery backup on every level of the home and outside sleeping areas. The U.S. Fire Administration adds that alarms belong in a central location outside each separate sleeping area. The CPSC also advises against putting alarms in attics or basements unless they include a sleeping area, and against spots near heating vents or places where furniture or draperies could cover the alarm.

How often should I test my CO alarm?

The CPSC recommends testing smoke and CO alarms monthly and replacing their batteries every year. Pressing the test button checks the alarm's circuitry, not how accurate its sensor is. When you buy a new alarm, choose one that meets the current UL 2034 safety standard.

What should I do if my carbon monoxide alarm goes off?

Follow the CPSC's steps. Do not try to find the source of the CO. Immediately move outside to fresh air, then call your emergency services, fire department, or 911. After calling 911, do a head count to check that everyone is accounted for. Do not go back inside until the emergency responders have given you permission. If the source turns out to be a malfunctioning appliance, the CPSC says not to operate it until it has been properly serviced by trained personnel. If authorities allow you to return to your home and your alarm reactivates within a 24 hour period, the CPSC says to repeat the first three steps: move outside, call 911, do a head count, and stay out until the emergency responders give you permission. If that happens, the CPSC also says to call a qualified appliance technician to investigate for sources of CO from all fuel burning equipment and appliances, and inspect for proper operation of this equipment.

What are the symptoms of carbon monoxide poisoning?

The CDC lists the most common symptoms as headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. The CPSC lists headache, fatigue, shortness of breath, nausea and dizziness as symptoms of low to moderate CO poisoning, and notes that the first symptoms are similar to the flu, but without the fever. The CDC also warns that people who are sleeping, drunk, or under the influence of other substances can die from CO poisoning before they have symptoms. If you suspect CO poisoning, the CPSC says to get outside to fresh air immediately, and then call 911.

Is smelling gas the same as a carbon monoxide problem?

No. Carbon monoxide has no color or smell, so a gas odor is a separate warning with its own steps. The CPSC's advice is that if you smell gas or hear gas leaking, you should leave your home immediately and contact local gas authorities from outside the home. The CPSC also says not to operate any electronics, such as lights or phones, before leaving. A CO alarm means something different: get outside to fresh air immediately and then call 911. Both situations start with getting everyone out of the house.

How often should a gas furnace be inspected?

Once a year. The CDC advises having your heating system, water heater, and any other gas, oil, or coal burning appliances serviced by a qualified technician every year. The CPSC gives the same yearly guidance and says the inspector should also check chimneys and flues for blockages, corrosion, partial and complete disconnections, and loose connections.

Staying Warm and Safe This Winter

For a Phoenix home with a gas furnace, the safety agencies recommend a few simple things: working CO alarms on every level and outside the sleeping areas, a monthly test, and a yearly inspection by a qualified technician. If an alarm ever sounds, get everyone outside to fresh air immediately and call 911. If you smell gas, leave immediately without operating any electronics, such as lights or phones, and call the gas authorities from outside.

Want a technician to look over your furnace, or help deciding where your alarms should go? Call us at (480) 689-5167 or send us a note through our contact page. We're glad to walk through it with you.