A smoky smell in an idle fireplace and a fuel-gas smell are different concerns. Odor does not identify the source or measure carbon monoxide.
Published by Chimney Sweep Pages · September 24, 2026 · Editorial method
First decision
A gas smell or possible CO exposure needs an emergency response, not a cleaning appointment.
Possible explanations—not a diagnosis
Deposits releasing odor in humid conditions
Air moving down the chimney into the house
Moisture, animal material or a damaged vent connection
Several conditions can occur together. Only an appropriate on-site assessment can distinguish them in your home.
What the investigation should clarify
The investigation should distinguish odor from deposits, moisture and airflow. Ask whether the company will inspect the venting route as well as sweep. An odor returning immediately after cleaning is a reason to reassess the cause, not repeatedly buy deodorizing treatment.
CO is odorless. A pleasant-smelling room is not evidence that combustion gases are absent.
One question worth asking
What evidence supports the suspected odor source, and what will you check if cleaning does not resolve it?
Ask for the findings, access limitations and proposed next steps in writing. Keep diagnosis separate from a repair estimate so you can seek another opinion with the same evidence.