The common rule
A common recommendation is to have a chimney inspected once a year and swept when it needs it. That is a good starting point, not a rule that fits every house.
The inspection tells you if a sweep is needed.
How much you burn
A fireplace used a few times a season builds up creosote slowly. A wood stove used as a main heat source can build it quickly.
More burning means more frequent cleaning.
What you burn
Wet, green wood makes more smoke and more creosote. Dry hardwood burned hot makes much less.
Treated or painted wood should never be burned.
How you burn
Smoldering, damped-down fires make cooler smoke and more buildup. A hot, bright fire with plenty of air keeps the flue cleaner.
Learning to burn well saves you cleanings.
Signs it needs cleaning now
Smoke smell, a lazy draft, black glass, soot falling into the firebox or flaky black material in the flue are signs.
Do not wait for the calendar if you see them.
Gas and pellet appliances
They make little creosote but still need yearly service for the vent and the burner or hopper.
Do not skip them because they look clean.
Have it inspected every year, sweep when the inspection says so and burn dry wood hot.
