I have found a few cracks in my chimney that I am about to hook up my wood stove to. I am not using a liner due to the ID of the chimney being only 4-1/2" x 8-1/2". From speaking to City of Portland inspectors, the dangers of not having your chimney lined lies mostly with carbon monoxide poisoning. However, I'm not UNcomfortable with this since I have carbon monoxide detectors and I will only being using the wood stove on an occasional basis. Like during those 5 really cold days in the Pacific Northwest.
But should I be worried about this type of small crack?