The answer to the startup question
A gas smell coming through your vents on every heating cycle should not be accepted as normal. Our recommendation is to treat it as a possible gas problem, have the immediate hazard checked, and have the furnace evaluated. Follow the responders' instructions about whether the furnace must remain off until that assessment is complete.
The fact that the smell goes away after a few minutes does not show that the furnace is safe. Atmos Energy warns that people can lose the ability to notice the odor, and that odor can fade under some conditions. Smell alone cannot clear a suspected leak. A repeating pattern is useful information for a professional, but it is not a home safety test. Atmos Energy safety guide.
Is this the same as dust burning off?
A brief dusty smell at the first use of the heating season is a different situation from a sulfur or rotten-egg odor that sounds like gas. Carrier distinguishes temporary dust odors from gas-related odors that need urgent attention. If you cannot tell which smell you have, do not try to settle the question by running the furnace longer. Follow the gas emergency steps. Carrier furnace odor guidance.
What needs to be checked after the emergency response?
The timing and an online description cannot tell us what caused the smell. Once the immediate hazard has been addressed, a qualified technician still needs to check your exact furnace.
A qualified technician should determine which checks are needed, using the furnace manufacturer's instructions. Relevant questions include whether fuel supply components leak, whether the burners light correctly, and whether the equipment vents properly. Gas valves, ignition components, the heat exchanger, and venting require appropriate professional judgment. These are areas to evaluate, not a list of parts you need replaced. Carrier furnace service guidance.
Ask for an explanation of the actual finding: “What did you test, what did you find, and what needs to happen before the furnace can run?” If the utility and service contractor are handling different parts of the problem, ask who owns the remaining work and who will confirm the furnace can be used. Permission to reenter the home and permission to use an affected appliance are separate questions.
What about carbon monoxide?
Carbon monoxide, or CO, has no smell. CDC CO explanation. It can be produced when fuel burns incompletely. A gas odor and a CO concern both deserve attention, but you cannot identify CO with your nose. If a CO alarm sounds, leave for fresh air and call 911. Check that everyone is outside. Stay out until emergency responders permit you to return. If a faulty appliance caused the carbon monoxide, keep it off until trained personnel have serviced it. If you suspect CO exposure because of symptoms such as headache, dizziness, or nausea, leave and seek prompt medical help. Do not wait for an alarm to confirm symptoms. CPSC carbon monoxide fact sheet.
Once everyone is safe, tell the service provider the pattern you already noticed: the odor begins with each heat cycle, comes through the vents, and later fades. Share any prior inspection or repair record. Do not recreate the smell to record a video or prove the problem.
The next step is a safe home and a clear finding. A replacement decision comes later, if the confirmed condition calls for it.