Lowes Chimney Sweep Blog

Your Carbon Monoxide Detector Goes Off Near the Fireplace: What Should You Do?

By the Lowes Chimney Sweep crew · Plano, TX

If your carbon monoxide detector is going off near the fireplace, take it seriously — carbon monoxide is a real, potentially deadly hazard, and the alarm is doing its job. This isn't a nuisance to reset and ignore. A CO alarm near a fireplace often means combustion gases that should be going up the chimney are instead coming into your home, and the fireplace or chimney is a likely source. Below, we'll cover exactly what to do right now, then why your chimney may be causing it and why you shouldn't use the fireplace again until it's inspected. But first, the immediate steps — because safety comes before diagnosis.

What to Do Right Now

If the CO alarm is sounding, act first and investigate later:

Get everyone to fresh air immediately. Move everyone, including pets, outside or to a well-ventilated area. Don't stay inside to investigate.

If anyone has symptoms — headache, dizziness, nausea, confusion, or drowsiness — call 911. These can be signs of carbon monoxide exposure and are a medical emergency.

Once everyone is safe, if it's safe to do so briefly, turn off the fireplace or any fuel-burning appliance and open doors and windows to ventilate.

Do not use the fireplace again until the cause has been found and fixed by a professional. Resetting the alarm and relighting the fire is exactly the wrong move.

Carbon monoxide is colorless and odorless, so the detector is your only warning. Never dismiss it as a false alarm without having the cause checked.

Why the Fireplace or Chimney Is a Likely Source

A fireplace, whether wood or gas, produces carbon monoxide as a byproduct of combustion. Normally that CO goes straight up the chimney and out. When the alarm sounds near the fireplace, it usually means that venting has failed — the CO is spilling into the room instead of leaving through the flue. That's a chimney problem at its core: something is stopping the exhaust from venting the way it should, and the CO detector is catching the result. This is why a CO alarm near the fireplace points so directly at the chimney and why a professional needs to find out what's wrong with the venting.

The Chimney Problems That Cause It

Here's what commonly stops a chimney from venting CO safely:

A blocked flue. A bird or animal nest, debris, or heavy creosote buildup can block the chimney so exhaust can't escape and backs up into the room. Clearing it is a chimney sweep or blockage removal.

A cracked or deteriorated flue liner. The liner keeps combustion gases inside the flue; when it's cracked, CO can leak into the home through the masonry — a serious safety issue addressed by liner repair.

Poor draft or backdraft. Negative pressure in a tight house, or a closed or stuck damper, can push exhaust back down into the room instead of up and out.

A flue in disrepair, where deterioration inside the chimney compromises safe venting and calls for flue repair.

Why This Requires a Professional Inspection

You cannot safely diagnose a CO problem yourself, and you should not keep using the fireplace hoping it was a fluke. The cause is inside the chimney — the flue, the liner, the draft — where you can't see, and identifying it takes a professional. A chimney inspection, typically a Level 2 inspection with a camera up the flue, checks for blockages, examines the liner for cracks, and evaluates whether the chimney is drafting properly. That's how the reason your fireplace vented CO into the room gets found and fixed. Given that carbon monoxide can be fatal, this is not a place to guess or delay — it's a place to get it professionally verified safe.

A Word on Your Detectors

Whatever the cause turns out to be, this is a reminder that working CO detectors are essential in any home with a fireplace or fuel-burning appliance — they're the only thing that can warn you of a gas you can't see or smell. Make sure you have them near the fireplace and sleeping areas, test them regularly, and replace them per the manufacturer's schedule. The alarm going off, as alarming as it is, means your detector did exactly what it's supposed to. The goal now is to find and fix why it triggered so it doesn't happen again.

How We Help

When you call us after a CO alarm near the fireplace, we treat it as the priority it is. We inspect the flue, liner, and draft — with a camera where needed — to find why the chimney vented combustion gases into your home, show you what we found, and fix the cause, whether that's clearing a blockage, repairing the liner, or correcting a draft problem. We won't clear the fireplace for use until we're confident it's venting safely. Your safety is the whole point, and we treat these calls accordingly, with same-day availability because this isn't something that should wait.

Why DFW Homeowners Call Lowes

A carbon monoxide warning near the fireplace is the kind of call where experience and thoroughness genuinely matter. Lowes Chimney Sweep is certified, insured, and 5-star rated across the Dallas-Fort Worth metroplex, we diagnose the venting problem properly and confirm safe operation before clearing the fireplace, and we offer same-day and Sunday service because a CO issue can't wait. If your CO detector has gone off near the fireplace, get to fresh air, call 911 if anyone has symptoms, and then call (214) 225-8874 to find out why — before you use that fireplace again.

After everyone is safe, a chimney inspection and Level 2 camera scan find why the chimney vented CO into your home — or request your Free Online Quote below.