Yes, fuel-burning HVAC equipment can be a carbon monoxide source when combustion or venting is not working the way it should. But a furnace is only one possible source in your home, and if an alarm is sounding or anyone feels sick, that is an emergency, not a troubleshooting project.
If a CO alarm is sounding right now, or anyone has symptoms
- Get everyone outside to fresh air, including pets.
- Call 911 from outside.
- Account for everyone who was in the home.
- Do not go back inside until the fire department or emergency responders say it is safe.
- Do not try to find the source, and do not silence the alarm.
Source: U.S. Consumer Product Safety Commission and Michigan Department of Health and Human Services. Call an HVAC company after responders have cleared your home, not before.
If you are reading this because you are worried and nothing is actively alarming, the rest of this guide walks through how furnaces and carbon monoxide are actually connected, what a homeowner can and cannot check, and how to lower your risk before heating season hits here in Oakland County.
What should you do if a carbon monoxide alarm sounds or someone has symptoms?
Leave the home for fresh air, call 911, and stay out until emergency responders or the fire department tell you it is safe to return.
That order matters. The CPSC says never to ignore an alarming CO alarm. Get people and pets outside first, then call from fresh air, then count heads to make sure everyone is out. MDHHS gives the same instruction for anyone who suspects carbon monoxide poisoning, has symptoms, or has an alarm going off.
An HVAC company is not the first call in this situation. We would rather lose a service call than have a family sitting inside a house waiting on a technician when they should be standing in the driveway talking to a dispatcher. Once responders have cleared the home, that is when a heating contractor belongs in the picture.
Put 911 first and your HVAC company second. Save your heating contractor's number in your phone now so you are not searching for it later, but call it after the emergency is handled.
Should you try to find the source or reset the alarm first?
No. The CPSC specifically says not to try to find the source of an active CO alarm and not to reenter the home until emergency responders allow it.
Carbon monoxide has no color and no smell, so there is nothing for you to follow. Walking around a house checking appliances means staying in the air that set the alarm off in the first place.
Silencing the alarm is the other common mistake. Hitting the button stops the noise but does nothing to the gas.
If your alarm is chirping rather than sounding a full alarm pattern, that is usually a low-battery or end-of-life signal. Check your alarm's manual for the exact difference between the two sounds on your model, and do it before an emergency, not during one.
Can symptoms tell you for sure that carbon monoxide is the problem?
No. CDC describes carbon monoxide symptoms as flu-like and nonspecific, which means symptoms are a reason to get out and get help, not a reason to diagnose the problem yourself.
A headache and an upset stomach could be a hundred things. That is exactly what makes carbon monoxide dangerous. Families have assumed a stomach bug was going around when the real issue was in the basement.
You also should not wait for symptoms before acting. If the alarm sounds and nobody feels sick, the response is the same.
If more than one person in the house feels sick at the same time, and everyone starts feeling better after being outside for a while, tell the 911 dispatcher and the medical staff that detail. It is useful information for them.
What causes a furnace to give off carbon monoxide?
A furnace gives off carbon monoxide when fuel does not burn completely, or when the exhaust cannot leave the home the way it is supposed to. CO is produced any time carbon-based fuel burns, so a gas- or oil-burning furnace is one of several household sources.
Here is the plain-language version. When fuel burns cleanly and the exhaust goes where it is supposed to go, the byproducts leave your home through the venting. When combustion is incomplete or the exhaust cannot get out, those byproducts have somewhere else to go.
Your furnace is not the only candidate. According to CDC's carbon monoxide basics, other fuel-burning sources in a typical home include water heaters, fireplaces, gas ranges, portable generators, and vehicle engines.
It is also worth being clear about what does not produce carbon monoxide. Equipment that does not burn fuel does not create CO. An electric furnace, a central air conditioner, and a heat pump are not combustion appliances.
Take two minutes and make a list of everything in your home that burns fuel. Furnace, water heater, fireplace, gas stove, gas dryer. That list is your actual carbon monoxide picture, not just the furnace.
What is the most common cause of carbon monoxide poisoning in a home?
Generators, not furnaces. CPSC reports that in 2020 the highest number of CO deaths tied to any single product category was 92, associated with generators. Portable heaters were second at 33.
That surprises people, and it is worth knowing before you assume the furnace is the problem. CPSC also reports that more than 200 people in the United States die each year from CO produced by non-automotive consumer products, a group that includes furnaces, water heaters, and room heaters.
The practical takeaway is not that your furnace is safe. It is that the source of any actual CO event has to be found by someone qualified rather than guessed at, because the likeliest culprit is not always the one you would name first.
If you own a generator, the single highest-value safety habit in this whole article is running it outdoors and well away from doors, windows, and vents. That one is on you, not on a technician.
What HVAC conditions should a qualified professional evaluate?
A qualified inspection can evaluate fuel-burning equipment and its venting, including flues and chimneys for blockages, corrosion, disconnections, and loose connections.
The CPSC recommends having a professional check the heating system, including vents, chimneys, and flues, every year. Those connection points are where problems tend to show up, and they are not things a homeowner is set up to assess.
A cracked heat exchanger is the condition most often named online, and it is one of the things a technician evaluates. It is worth being clear about what that means, though. A crack cannot be confirmed from a description, a photo, or a quick look. It takes a qualified inspection of the equipment itself, which is why you should be skeptical of anyone who diagnoses one over the phone.
An inspection is a scope of work, not a guarantee. A technician can check what is checkable, document what they find, and tell you what needs correcting. Nobody can hand you a promise that a house will never have a carbon monoxide event.
- Cleaning the burners and the heat exchanger
- Checking the ignition system
- Testing the safety controls
- Inspecting the flue and the venting
- Testing for gas leaks and checking gas valve operation and gas pressure
- Checking thermostat calibration
- Testing the full heat cycle for proper operation
Our technicians hold a Michigan Mechanical License and EPA certification. When we finish, we go over what we found with you before we leave.
If something is found, the fix depends on the finding. Some issues are a straightforward furnace repair in Oakland County. Others point toward furnace replacement options, and that call comes after the inspection, not before it.
Ask for the inspection findings in writing. A written record gives you something to compare against next year, and it gives you documentation if you ever sell the house.
Can a homeowner's visual check prove that the system is safe?
No. Because carbon monoxide cannot be seen or smelled, nothing you observe by looking at your furnace can clear a fuel-burning appliance or rule out a CO hazard.
There is a lot of advice online about flame color and other quick visual tests. A visual observation can tell you that something looks off and is worth a service call. It cannot tell you that everything is fine.
That is the distinction to hold onto. "Looks normal" is not a safety clearance. Working CO alarms and qualified annual service are what actually reduce your risk.
If something about your furnace looks or sounds different from normal and no alarm is going off, that is a non-emergency service call. Write down what you noticed and when, so the technician has something to work with.
What are the warning signs and symptoms of carbon monoxide exposure?
Common symptoms include headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion, and they should never be used to self-diagnose carbon monoxide poisoning.
CDC lists those as the most common symptoms and notes they are often described as flu-like. High exposure can cause loss of consciousness or death.
There is one detail from CDC that every homeowner should know. People who are sleeping, or who have been drinking, can die from carbon monoxide before they ever notice a symptom. That is why working alarms near sleeping areas matter so much.
If anyone has these symptoms, get to fresh air and get medical help right away. Do not drive yourself.
Symptoms that improve when you leave the house and come back when you return are worth mentioning to a doctor. Do not talk yourself out of it because the timing seems like a coincidence.
Who is more likely to get sick from carbon monoxide?
CDC identifies infants, older adults, and people with chronic heart disease, anemia, or breathing problems as groups more likely to get sick from carbon monoxide exposure.
That does not mean anyone else is safe. It means the margin is thinner for some people in the house, and it is a good reason to be more careful about alarm placement and annual service if any of those household members are yours.
This is general safety information, not medical guidance. Specific health questions belong with a doctor.
If you have a nursery or a bedroom where an older parent sleeps, treat alarm coverage near those rooms as a priority rather than an afterthought.
Where should carbon monoxide alarms be placed and maintained?
Follow your alarm manufacturer's instructions first, and use CO alarms near sleeping areas and on every level of the home as recommended by CDC, CPSC, and NFPA.
CDC recommends battery-operated alarms or alarms with battery backup near every sleeping area. CPSC recommends alarms on every level of the home and outside sleeping areas, and advises against mounting them near heating vents or anywhere a curtain or furniture could block them.
The manufacturer's instructions control the details. Mounting height, spacing, testing schedule, and replacement age all vary by product, which is why a universal rule from a blog post is worth less than the paper that came in the box.
MDHHS goes one step further for Michigan homes and recommends 10-year lithium battery CO detectors on every level and near all sleeping areas. Sealed long-life units take the dead-battery problem off the table.
One more thing the CPSC is direct about. Alarms are added protection. They do not replace proper installation, proper use, upkeep, and professional inspection of fuel-burning appliances.
Keep the alarm manual in the same drawer as your other appliance paperwork, or snap a photo of the model number and the instructions with your phone. You will want it when the alarm starts chirping at 2 a.m.
Does the test button confirm that the CO sensor is accurate?
No. The CPSC says the test button checks whether the alarm circuitry is working, not whether the sensor is still accurate.
That surprises most homeowners. Pressing the button and hearing a beep confirms the horn and the electronics respond. It says nothing about whether the sensing element inside can still detect carbon monoxide correctly.
Sensors age. That is why manufacturers put a replacement date or an end-of-life signal on the product, and why the manufacturer's number is the one to follow rather than a general figure you read somewhere.
Write the purchase date on the back of each alarm with a marker when you install it. Then you are not guessing about its age five years from now.
Do Michigan rules require carbon monoxide alarms?
Michigan law describes carbon monoxide device requirements for specific situations, including initial construction, certain permitted renovations, and adding or creating a bedroom.
Michigan Compiled Laws 125.1504f, known as the Overbeck law, describes placement in the vicinity of bedrooms, in areas within the dwelling adjacent to an attached garage, and in areas adjacent to any fuel-burning appliances. It has been in effect since March 23, 2009.
The law allows four kinds of device: battery powered, plug-in with or without battery backup, wired into the home's AC power with secondary battery backup, or connected to a system through a control panel.
Read that carefully, because it is narrower than "every Michigan home must have one." The requirement is tied to the type of work being done and the permit situation, which is why questions about your specific house belong with your local building official.
Code also changes. Anything you read about code status, including this paragraph, should be confirmed with the authority having jurisdiction in your city or township before you rely on it.
If you are pulling a permit for a remodel or a bedroom addition in Oxford, Lake Orion, Clarkston, or anywhere else in Oakland County, ask your building department about carbon monoxide device requirements while you are already on the phone with them.
How can Southeast Michigan homeowners lower carbon monoxide risk before heating season?
Annual qualified service for fuel-burning equipment, working CO alarms, proper venting, and safe use of generators and other combustion equipment all reduce carbon monoxide risk.
None of those four items is optional if you want the risk actually lowered, and none of them is a guarantee on its own. They work as a set.
| Task | How Often | Who Does It |
|---|---|---|
| Professional inspection of the furnace, vents, chimney, and flue | Once a year, before heating season | Qualified HVAC technician |
| Test every CO alarm | Per manufacturer instructions | Homeowner |
| Replace alarms at end of life | Per manufacturer instructions | Homeowner |
| Check that exterior vents are clear | After snow and ice events | Homeowner |
| Confirm generators are used outdoors only | Every use | Homeowner |
Fall is the right time for the professional piece. If you want it handled on a schedule instead of remembering it yourself, you can schedule a furnace tune-up or put it on autopilot with our VIP maintenance plan.
Tie your alarm test to something you already do seasonally, like changing your furnace filter. Habits stick better when they ride along with an existing one.
Why should furnace and other exterior vents be checked after snowstorms?
NFPA advises clearing snow buildup from furnace, dryer, stove, and fireplace vents during and after a snowstorm.
This is the Southeast Michigan detail that national articles skip. We get heavy wet snow, drifting, and the freeze-thaw cycle that packs ice against the side of a house. High-efficiency furnaces vent through a PVC pipe out a sidewall, often low to the ground, which is exactly where snow piles up.
Blocked exhaust is a venting problem, and venting problems are part of the carbon monoxide picture.
Walk your foundation line after a big storm and look for the plastic vent pipes coming out of the wall. Clear them by hand or with a broom, not with a shovel blade that can crack the pipe.
What generator and garage rules belong in a furnace safety guide?
Generators belong outdoors and away from the home, and vehicles or other fuel-burning engines should never run in an enclosed space like a garage.
CDC and CPSC both put the generator distance at least 20 feet from doors, windows, and vents. That 20-foot figure is specific to generators. Do not apply it to your furnace vent as if it were a general rule.
The garage rule is simpler and gets broken constantly. Warming up a car in an attached garage puts exhaust right next to your living space, and opening the garage door does not fix it.
Power outages are when this gets dangerous in Michigan. A storm knocks out power, the furnace is down, and people start improvising with generators and grills.
Decide where your generator goes before the next outage, and make sure that spot is well away from doors, windows, and vents. Choosing a location by flashlight in a snowstorm is how bad decisions get made.
What does Michigan data say about carbon monoxide risk?
MDHHS reports that Michigan averages 849 emergency department visits, 115 hospitalizations, and 34 deaths each year from unintentional carbon monoxide poisoning, based on 2018 through 2022 data.
Those are statewide averages covering unintentional fire and non-fire CO exposures across that five-year period. They are not an Oakland County number, and they are not a prediction about any individual home.
We include them because homeowners often treat carbon monoxide as a rare, far-away problem. Michigan's heating season is long, most homes here burn fuel for heat, and the numbers reflect that.
Use this as a scheduling nudge, not a scare. One annual inspection and a set of working alarms handle most of what a homeowner can control.
When should you call a qualified HVAC professional?
Call after emergency responders have cleared an alarm, or any time you have a non-emergency concern about a fuel-burning appliance and want it inspected.
Those are two different calls. The first one happens after the fire department has done its part and you need the equipment looked at. The second one is the call you make because something seems off, or because it is fall and the furnace has not been serviced.
Oakland Heating & Cooling has served Oxford and Oakland County since 2000, operating through J.R.S. Mechanical, Inc. Owner John Serrano has been in the HVAC trade since 1995. Our in-house team handles every repair rather than subcontractors, our technicians hold a Michigan Mechanical License and EPA certification, and we are an authorized Rheem dealer. We offer same-day service to get your heat back on fast.
One clarification worth making, because it comes up. Indoor air quality services like filtration and purification handle dust, allergens, and other air quality concerns. They are not carbon monoxide protection. Nothing replaces CO alarms and qualified inspection of fuel-burning equipment.
Book your furnace inspection in September or early October. Once the first real cold snap hits Southeast Michigan, every HVAC company in the county is running repair calls and the schedule tightens up fast.
Frequently Asked Questions
Can a water heater cause carbon monoxide poisoning?
A fuel-burning water heater is one of several household appliances CDC lists as a potential carbon monoxide source. That is why the source of an alarm needs to be evaluated properly rather than assumed to be the furnace. If an alarm sounds, get out and call 911 first, then have the fuel-burning equipment in the home inspected.
Does opening windows make a carbon monoxide situation safe?
No. MDHHS puts it plainly: you will not stop CO buildup by opening windows or doors. CO collects in enclosed and partially enclosed spaces regardless. Ventilation is not an emergency response. Leaving the space and calling 911 is.
Is there an acceptable carbon monoxide level for a furnace?
There is no single number a homeowner can use to clear a furnace. Meaningful readings depend on the instrument, where and how the measurement is taken, the equipment itself, and a qualified technician interpreting the result. A consumer reading from an inexpensive meter is not a safety clearance, and no reading replaces the emergency response when an alarm sounds.
Can an electric furnace or air conditioner produce carbon monoxide?
No. Carbon monoxide is produced when carbon-based fuel burns, so equipment that does not burn fuel does not create it. Electric furnaces, central air conditioners, and heat pumps are not combustion appliances. Keep in mind that a home with electric heat may still have a gas water heater, fireplace, or range.
Does a working CO alarm mean my furnace does not need maintenance?
No. The CPSC is explicit that carbon monoxide alarms are added protection and not a substitute for proper installation, use, upkeep, and professional inspection of fuel-burning appliances. An alarm tells you something has already gone wrong. Annual service is what reduces the odds of getting there.
How often should I test my carbon monoxide alarm?
The CPSC recommends testing carbon monoxide alarms monthly and following the manufacturer's instructions for battery service and replacement. Some models use sealed long-life batteries, so check what your specific alarm calls for. Remember that the test button verifies the circuitry, not the sensor's accuracy.
Can I use my gas oven to heat my house if the furnace stops working?
No. CDC and CPSC both say not to use a gas oven or range to heat a home. If your heat goes out in the middle of a Michigan winter, that is a service call, not a reason to improvise. Our furnace repair team handles no-heat calls, and this related guide covers how long it takes for pipes to freeze after a furnace failure.
Sources
- Carbon Monoxide Poisoning Basics, Centers for Disease Control and Prevention
- Carbon Monoxide Fact Sheet, U.S. Consumer Product Safety Commission
- Carbon Monoxide, Michigan Department of Health and Human Services
- Carbon Monoxide Safety, National Fire Protection Association
- Michigan Compiled Laws 125.1504f, Carbon Monoxide Devices
