Carbon Monoxide and Your Furnace: Pennsylvania Guide
You can't see it, smell it or taste it, which is why the alarm does the noticing for you.
Every furnace, boiler, water heater and fireplace that burns oil, propane, gas or wood can make carbon monoxide when something goes wrong. This guide explains where CO comes from in a house, what poisoning feels like, where alarms belong, what Pennsylvania's Act 121 requires, and what a proper CO check from a heating technician looks like.
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What is carbon monoxide?
Carbon monoxide (CO) is a colorless, odorless, tasteless gas made when fuel burns incompletely. It binds to the blood in place of oxygen. The EPA explains that it forms carboxyhemoglobin, which cuts the oxygen the body can carry. The CDC says heavy exposure can cause people to pass out or die.
Every appliance that burns oil, propane, natural gas, wood, gasoline or charcoal can produce CO. A well-tuned, well-vented furnace sends almost all of it outside. Problems start when combustion goes wrong or the exhaust has nowhere to go but indoors.
The EPA puts typical CO levels in homes without gas stoves at about 0.5 to 5 parts per million (ppm). Readings near a well-adjusted gas stove are often 5 to 15 ppm, and 30 ppm or more near a poorly adjusted one. A technician's meter reads in the same units.
What are the sources of carbon monoxide in a home?
The common sources are furnaces and boilers with damaged heat exchangers or blocked flues, chimneys and vent pipes that leak or backdraft, gas or oil water heaters, fireplaces and wood stoves, gas ranges, unvented space heaters, portable generators, and cars running in attached garages. The EPA and CDC list all of these.
| Source | How CO gets indoors | Warning signs |
|---|---|---|
| Furnace heat exchanger | Cracks or rust holes let combustion gas mix with house air | Soot, rust flakes, flames that waver when the blower starts |
| Flue or vent pipe | Disconnected, rusted or blocked pipe spills exhaust | Loose joints, rust, white or dark staining at seams |
| Chimney | Blockage from nests, debris or a collapsed liner forces exhaust back | Crumbling mortar, debris at the cleanout, poor draft |
| Water heater | Backdrafting at the draft hood, especially in an oversized flue | Scorched or melted material near the draft hood |
| Oil burner | Poor combustion, delayed ignition, puffbacks | Soot, oily smell, bang or whoosh on startup |
| Fireplace or wood stove | Closed damper, weak draft, leaky stove door | Smoke in the room, smell of smoke after the fire |
| Portable generator | Run indoors or too close to openings | Exhaust smell, alarms during outages |
| Attached garage | Car or equipment exhaust seeps through the house door or walls | Exhaust smell in rooms next to the garage |
What are the symptoms of carbon monoxide poisoning?
The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, often described as flu-like. Heavy exposure can cause fainting and death. People who are asleep or intoxicated can die before they notice symptoms. Infants, older adults and people with heart or breathing problems are more likely to get sick.
The EPA notes one clue that separates CO from the flu: symptoms that ease after you leave the house. If several people, or people and pets, feel ill at once at home, treat it as CO until proven otherwise.
If a CO alarm sounds
- Get everyone outside to fresh air right away, including pets.
- Call 911 from outside, not from inside the house.
- Don't go back in until responders say it's safe.
- Seek medical care for anyone with symptoms.
- Have the heating system checked before using it again.
- Don't assume a false alarm. Kidde says a digital reading with no alarm can still mean CO is present.
Where should carbon monoxide alarms go?
The CPSC says to put battery-operated or battery-backup CO alarms on every level of the home and outside sleeping areas, and that interconnected alarms work best. The CDC also says to place them near every sleeping area. Follow the alarm maker's instructions for height and distance from appliances.
- One outside each sleeping area, close enough to wake sleepers
- One on every level, including the basement where the furnace or boiler is
- One in rooms next to an attached garage
- Interconnected alarms, so one sounding sets off all of them
- Battery backup on any plug-in or hard-wired alarm, so it works in an outage
- Check batteries when clocks change in spring and fall, as the CDC suggests
A smoke alarm doesn't detect CO unless it's labeled as a combination alarm. Check the label.
How long do carbon monoxide alarms last?
Most CO alarms last 5 to 10 years. Kidde says its alarms made since 2013 generally last 10 years, and some models and older units 7 years. The CDC says to replace alarms per the manufacturer or about every 5 years. Check the date on the back and replace the alarm when it signals end of life.
| Source | Lifespan guidance | Notes |
|---|---|---|
| Kidde | 7 to 10 years by model | Most made since 2013 last 10 years; follows NFPA guidance on replacement |
| CDC | Per manufacturer, or about every 5 years | Check batteries spring and fall |
| InterNACHI life expectancy chart | About 5 years | Change batteries at least once a year |
Kidde describes end-of-life signals as a chirp or beep every 30 seconds that a new battery won't stop, or an ERR or END code on digital models. Kidde warns that an alarm in end-of-life mode can't detect CO. Replace it right away.
What does Pennsylvania's Act 121 of 2013 require?
Act 121, the Carbon Monoxide Alarm Standards Act, took effect December 18, 2013. Home sellers must disclose CO detector information on the property disclosure statement. Multifamily units with a fossil fuel-burning heater or appliance, a fireplace or an attached garage need a working, approved CO alarm near the bedrooms and the heater or fireplace.
| Who | Responsibility under Act 121 |
|---|---|
| Seller of a residential building | Disclose information about CO detector installation on the property disclosure statement |
| Owner of a rented multifamily unit | Provide and install an approved alarm where required; replace missing or dead alarms and make sure batteries work before a new occupant moves in |
| Tenant | Keep the alarm in good repair, test it, replace batteries, replace a missing or broken alarm during the tenancy, and notify the owner in writing of problems |
| Owner after move-out | Responsibility returns to the owner while the unit is vacant |
Summaries of the act describe willful failure to install or maintain a required alarm as a summary offense with a fine of up to $50. The act doesn't set a statewide alarm mandate for single-family homes, though some municipalities have their own rules. Either way, alarms belong in every home with a fuel-burning appliance, fireplace or attached garage.
This is a plain-English summary, not legal advice. For a sale or rental, confirm details with your agent, attorney or the township. More on Pennsylvania rules.
Can a cracked heat exchanger cause carbon monoxide?
It can. The heat exchanger is the metal wall that keeps combustion gases separate from the air the blower sends through the house. A crack or rust-through can let exhaust mix into that air, especially when the blower is running. A cracked heat exchanger is a safety finding, and the furnace should be shut off until it's resolved.
Heat exchangers crack from age, repeated overheating and corrosion. Clogged filters, blocked returns and oversized furnaces cause overheating. Damp basements speed up rust. If a technician reports a crack, ask to see it: a camera image, a photo or a combustion reading that changes when the blower starts.
Backdrafting and orphaned water heaters
Backdrafting is when exhaust flows back into the house instead of up the flue. The EPA lists back-drafting from furnaces, water heaters, wood stoves and fireplaces as a CO source.
A common cause in older homes is an orphaned water heater: one left alone in a chimney after the furnace or boiler moved to PVC venting. InterNACHI explains that the flue, sized for two appliances, may be too big for the water heater alone to draft, so exhaust can spill at the draft hood. Fixes include a properly sized liner or replacing the water heater.
Strong exhaust fans, a clothes dryer and a tight house can also pull exhaust backward. A draft test catches this.
What should a technician's carbon monoxide test include?
A proper check measures CO in the living space before work starts, tests combustion in the flue with a calibrated analyzer, checks draft at the furnace and water heater, inspects the heat exchanger and venting, and records the readings. The EPA advises annual inspection of furnaces, flues and chimneys by a trained professional.
- Measures ambient CO inside the house on arrival.
- Inspects the vent pipe, chimney connector or PVC runs for gaps, rust and slope.
- Checks the heat exchanger, with a camera where needed.
- Runs a combustion analysis in the flue, not just at the register.
- Watches the flame and the reading as the blower comes on.
- Tests draft at every atmospheric appliance on the chimney, including the water heater.
- Repeats the draft test with exhaust fans and the dryer running.
- Writes down readings and explains anything out of range.
Ask for numbers. A good technician can tell you the CO reading in the living space and in the flue, and what each means. "It looks fine" isn't a test.
Oil systems also get a smoke test and draft reading at the yearly cleaning. Gas and propane systems get gas pressure and temperature rise checks. All of it belongs in a fall furnace tune-up.
Get connected with a local heating company and ask for combustion and CO readings in writing. The referral is free.
Carbon monoxide risks in Unionville-area homes
Unionville has a mix of homes that each carry their own CO risks: old masonry chimneys in the historic village and farmhouses, oil burners that need yearly cleaning, attached garages in newer subdivisions, generators during storm outages, and barns and workshops with unit heaters. Each needs alarms and regular checks.
Old chimneys
Many village and farmhouse chimneys were built for wood or coal, long before modern furnaces. Liners crack, mortar fails, and flues end up oversized for today's appliances. CSIA cites NFPA 211 in calling for yearly chimney inspections. See heating old stone homes.
Oil burners
Oil is still common past the gas lines. A dirty nozzle or poor adjustment causes incomplete combustion, soot and puffbacks. Soot around the burner or registers is a reason to shut the system off and call. More in oil furnace repair.
Attached garages
Newer homes in East Marlborough often have attached garages. The CDC says never to run a car in an attached garage, even with the door open. Put a CO alarm in rooms next to the garage.
Barns, studios and outbuildings
Propane unit heaters in barns and workshops need venting and clearance checks like any furnace. People and animals spend hours in these spaces. A CO alarm there is worth the small cost.
Storm outages
Generators run during ice storms are a leading CO risk. See power outages and heat for safe distances.
How do you prevent carbon monoxide problems from heating?
Have every fuel-burning appliance and chimney inspected yearly, keep vents and flues clear, install and test CO alarms, and never use ovens, grills, camp stoves or generators for indoor heat. Replace filters so the furnace doesn't overheat, and ask about draft whenever a furnace, boiler or water heater changes.
- Yearly service for furnaces, boilers, water heaters and chimneys
- Clear snow from high-efficiency PVC intake and exhaust pipes after storms
- Change filters on schedule, monthly in winter if you have pets or barn dust
- Never heat a home with a gas oven, as the CDC warns
- Open the damper whenever the fireplace is in use
- Never idle a car in the garage
Carbon monoxide questions from Pennsylvania homeowners
Can a furnace leak carbon monoxide when it's off?
A furnace that isn't burning fuel doesn't make CO. But other appliances on the same chimney, like a water heater, can still backdraft. If an alarm sounds with the furnace off, leave and call 911 anyway.
Does Pennsylvania require CO alarms in single-family homes?
Act 121 doesn't set a statewide mandate for single-family homes. It requires disclosure when a home is sold and alarms in certain multifamily units. Some municipalities have their own rules, so check locally. Every home with fuel-burning heat should have alarms regardless.
Who replaces the CO alarm batteries in a rental?
Under Act 121, the owner makes sure alarms work and batteries are good when a new tenant moves in. During the tenancy, the tenant tests the alarm, replaces batteries and tells the owner in writing about problems.
What should I do if my CO alarm keeps chirping?
A regular chirp is often a low battery or end of life. Kidde says a chirp every 30 seconds that a new battery won't stop means the alarm needs replacing. A full alarm pattern is different: leave and call 911.
Can a heat pump produce carbon monoxide?
No. ENERGY STAR notes heat pumps produce no combustion emissions such as carbon monoxide. If you have a heat pump with a gas, oil or propane backup furnace, the furnace can still produce CO.
How do I know if my heat exchanger is cracked?
You usually can't tell yourself. A technician looks for cracks, rust-through and flame changes when the blower starts, often with a camera and a combustion analyzer. Ask to see the evidence before agreeing to a replacement.
How often should my furnace be checked for carbon monoxide?
Once a year. The EPA advises having a trained professional inspect, clean and tune furnaces, flues and chimneys annually, and the CDC says to service fuel-burning appliances yearly. Ask for CO readings at every visit, not only at tune-ups.
Is this site a heating contractor or safety inspector?
No. UnionvillePAFurnaceRepair is a free referral service that connects you with independent local HVAC companies. It doesn't inspect or repair equipment and may be paid for referrals. For an active alarm, call 911, not this line.
Sources
- CDC: About carbon monoxide poisoning (symptoms, yearly deaths, prevention).
- EPA: Carbon monoxide's impact on indoor air quality.
- CPSC: Carbon Monoxide Information Center (alarm placement).
- Kidde: CO alarm replacement and end-of-life signals.
- InterNACHI: Standard estimated life expectancy chart and Orphaned water heaters.
- Pennsylvania General Assembly: Act 121 of 2013, Carbon Monoxide Alarm Standards Act (title, date, effective immediately).
- Middletown Township, Bucks County: CO Act 2013 summary.
- abc27: What are Pennsylvania's laws on carbon monoxide alarms?
- Chimney Safety Institute of America: homeowner resources.
- ENERGY STAR: Air-source heat pumps (no combustion emissions).
Written by Lawrence. Updated October 25, 2026. Facts on this page were checked against the public sources listed above.
This is general information from a free referral service, not a heating contractor. For gas smells or carbon monoxide alarms, leave the house and call 911.
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