Where the levels come from
The three inspection levels are defined in NFPA 211, the national standard for chimneys and venting. They are not marketing tiers invented by companies — they describe how far into the structure the inspection goes.
Level 1: the annual inspection
This is what you need if your system has not changed and you are using it the way you always have.
The technician examines the readily accessible portions of the chimney exterior and interior, the accessible portions of the appliance and the connection, the firebox, the damper, the smoke chamber, and the flue as far as can be seen from top and bottom. They confirm the flue is clear of obstruction and combustible deposits, and that the basic structure is sound.
It is the inspection that accompanies a routine sweep, and for most homes it is the only one ever needed.
Level 2: when something has changed
Required when you change anything material — a new appliance, a different fuel, a relining — and on the sale or transfer of a property. Also after any event that could have damaged the chimney: a chimney fire, an earthquake, a severe storm.
It includes everything in Level 1 plus accessible attics, crawl spaces and basements where the chimney passes through, and a video scan of the internal flue surfaces. It does not involve removing any part of the building.
Level 3: when access has to be opened
Reserved for cases where a serious hazard is suspected and cannot be confirmed any other way. It may require removing parts of the chimney crown or interior wall. It is rare and it is not something a homeowner books casually.
What you should get on paper
A written report, whichever level you buy. It should say what was examined, what was found, and what condition the liner, damper, crown and cap are in.
If you are buying a house with a fireplace, ask for a Level 2 specifically. A Level 1 on an unknown chimney tells you almost nothing, and a flue that has had a fire in it can look perfectly normal from the firebox.