How Often
The frequency depends on what you burn and how much, and the inspection matters more than the sweeping.
Short answer
Annually as a baseline for any chimney in use, and more often with heavy wood-burning — some regular users need it mid-season. A gas appliance flue needs inspection annually even though it does not produce creosote. An unused chimney still needs inspecting, because the deterioration and the animals carry on regardless.
By appliance and use
Open wood fireplace used regularly: annually, and inspect mid-season if use is heavy.
Wood stove or insert used as a primary heat source: potentially two or three sweeps a season, because the volume of wood burned is far higher.
Occasional wood fireplace use: annually, and the inspection is the main value.
Gas fireplace or gas appliance venting into the chimney: annually for inspection — no creosote, but there is debris, deterioration, blockage and animals.
Oil appliance: annually, with the soot and the acidic condensate being the issues.
And an unused chimney: inspect every couple of years, because the crown, the flashing, the tiles and the animals do not care that it is unused.
The inspection is the point
Sweeping removes what is there. The inspection tells you what is wrong, and on a Toronto chimney what is wrong is frequently the crown, the flashing, the cap, cracked tiles or a deteriorating smoke chamber. A sweep who only sweeps is doing half the visit.
What should be inspected
The flue interior, ideally with a camera on an appliance in regular use.
The liner condition: cracked, spalled or missing tiles, and gaps at the joints.
The smoke chamber and the smoke shelf, which deteriorate and which collect debris.
The damper, which rusts and jams.
The firebox, the firebrick and the mortar joints inside it.
And the exterior: the crown, the cap, the pointing, the flashing at the roof line and the termination height.
Signs it needs doing sooner
Visible deposit more than a few millimetres thick when you look up with a light and a mirror.
A smoky smell in the room, particularly in humid weather or when the furnace runs.
Smoke spilling into the room when lighting a fire.
Debris falling into the firebox, which means tiles or mortar are failing.
Birds or animals heard in the flue.
And any change: a new appliance, a reroof, a new high-efficiency furnace that took itself off the chimney, or a chimney fire.
Common questions
How often should a Toronto chimney be swept?
Annually as a baseline, and more often with heavy wood-burning.
Does a gas fireplace flue need attention?
Annual inspection, yes. No creosote, but debris, blockage and deterioration all happen.
What about an unused chimney?
Inspect it every couple of years. The crown, flashing and animals carry on regardless.