A full sweep plus a Level 1 safety inspection of the flue, damper and cap. Booked before the cold sets in, not during the January backlog.
Burning wood leaves a tar-like glaze inside the flue. Once it is thick enough, a hot fire in the firebox can ignite the whole chimney.
Nests, leaf litter and a collapsed cap send combustion gases back down into the room instead of up and out.
You get the flue condition, damper operation and cap status documented — which is also what a home insurer asks for.
September and October fill up fast. By December most sweeps in the area are three weeks out.