What to ask before the visit
CPSC recommends annual professional inspection of fuel-burning heating systems, including their flues and vents. That recommendation is not limited to old equipment. CPSC fuel-burning equipment guidance.
Ask the provider to identify your furnace's model, vent arrangement, and applicable inspection instructions. Ask how the visit will address burner operation, combustion measurements when appropriate, the path that carries exhaust outdoors, and possible heat-exchanger deterioration. The heat exchanger transfers heat while separating the combustion-gas path from the household-air path.
For example, the Lennox SLP99DFVK owner's manual lists professional checks for heat-exchanger integrity, combustion air, and intake and exhaust condition. That manual illustrates the need for an equipment-specific checklist; your installed model's instructions govern. Lennox example professional inspection.
Understand a finding before choosing work
Ask for the observed condition, test method, result, and any limit on what was visible. If a cracked or damaged heat exchanger is reported, ask for the supporting evidence and the qualified recommendation for operation and correction. One satisfactory reading should not be presented as a guarantee that every part of the furnace is sound.
A real safety finding may require taking equipment out of use. Do not keep operating it simply to obtain another opinion. A qualified second opinion can review the evidence while the furnace remains off as directed.
An active warning changes the order
If a CO alarm sounds, move outside to fresh air and call 911. Stay out until emergency responders permit return. Have a qualified technician identify and correct the combustion source before the affected appliance is used again. Permission to enter is separate from appliance clearance. CO reentry and source correction. CO is carbon monoxide, a poisonous gas you cannot smell. Do not wait for a maintenance appointment or search for the source. CPSC alarm response.
For a routine appointment, your next step is to ask for the exact combustion-safety scope and a written findings record. Decide about repair or replacement from those findings, not from age alone.