Of everything we talk about with homeowners, this is the one we take most seriously. A gas furnace is a safe, efficient way to heat your home when it's working properly — but a furnace that isn't maintained can, in rare cases, produce carbon monoxide. Because you can't see it or smell it, understanding the risks and the safeguards isn't optional. It's how you protect your family. Here's what you need to know before heating season.
What Carbon Monoxide Is — and Why It's So Dangerous
Carbon monoxide, or CO, is a gas produced when fuel burns. It's completely colorless and odorless, which is exactly what makes it dangerous: there's no natural way for you to detect it. When CO builds up in a home, it can make people and pets seriously ill, and at high levels it can be deadly. It doesn't announce itself — which is why the safeguards below matter so much.
How a Gas Furnace Can Produce CO
Your furnace burns natural gas to create heat, and it's designed to safely vent the resulting combustion gases out of your home. Problems arise when that process breaks down. The most common causes are:
- A cracked heat exchanger. This is the metal component that separates the combustion gases from the air blown into your home. If it cracks with age or stress, CO can leak into your living space.
- Poor or incomplete combustion. A dirty or malfunctioning burner can burn fuel improperly, producing more CO than it should.
- Blocked or damaged venting. If the flue or vent that carries exhaust outside is obstructed or disconnected, those gases can back up into the house.
None of these are common in a well-maintained furnace — but all of them are exactly what a professional inspection is designed to catch.
Warning Signs to Watch For
Two categories matter here: signs your furnace has a problem, and signs that people may be experiencing CO exposure.
Signs of a furnace issue:
- The burner flame is yellow or flickering instead of a steady blue
- Soot or scorch marks around the furnace
- Unusual or "burning" odors when the furnace runs (while CO is odorless, other combustion problems can produce smells)
- More condensation than usual on windows near the furnace
Signs of possible CO exposure:
- Headaches, dizziness, nausea, or fatigue
- Symptoms that feel like the flu but without a fever
- Symptoms that ease when you leave the house and return when you come back — a major red flag
- Multiple people (or pets) in the home feeling sick at the same time
The Two Protections That Matter Most
Everything comes down to two safeguards, and every home with a gas furnace needs both.
Working CO detectors. These are your early warning system — the one thing that can alert you to a gas you otherwise can't sense. Install them on every level of your home and near sleeping areas, test them regularly, and replace the batteries and the units themselves on schedule. This is inexpensive, life-saving equipment.
An annual furnace inspection. Before each heating season, have a professional inspect your furnace — including a check of the heat exchanger, the burners, and the venting. This is how problems get caught before they ever become a danger, and it's the single best maintenance habit for a gas-heated home.
What to Do If Your CO Detector Goes Off
Treat it as real, every time. Get everyone out of the house and into fresh air immediately, then call 911 or your gas company from outside. Don't go back in to investigate or "air it out" first. Once the situation is confirmed safe, have your furnace professionally inspected before running it again.
We'd always rather you be overly cautious here. If your gas furnace hasn't been checked recently, or you have any concern at all, call Perfect Service at 205-206-6091 for a heating-season safety inspection. Keeping your family safe from something you can't see or smell is the most important part of protecting your home.
Common Questions About Carbon Monoxide and Furnaces
No — and that’s precisely why it’s so dangerous. CO is completely odorless and colorless. A CO detector is the only reliable way to know it’s present, which is why every home with gas appliances needs working detectors.
Once a year, ideally before heating season begins. An annual inspection checks the heat exchanger, burners, and venting — the components whose failure could allow CO into your home.
On every level of your home and near sleeping areas, so an alarm will wake you. Test them regularly and follow the manufacturer’s guidance for replacing batteries and the detectors themselves.
The heat exchanger keeps combustion gases separate from the air you breathe. A crack can let carbon monoxide into your home, so it’s a serious safety issue — and a key thing a professional inspection is meant to catch.
Yes. Always treat an alarm as real: get everyone outside into fresh air and call 911 or your gas company from outside. CO can affect you before you feel it, so never ignore or reset an alarm without getting to safety first.
