Creosote has a distinct smell.
Smell
Creosote has a strong, smoky smell, and can smell like a fresh-paved driveway made of asphalt. The smell of creosote can be likened to the smell of tar, and this creosote smell is easily picked up by the human nose even in small concentrations. The presence of creosote in a chimney can also result in a creosote smell throughout a home because the odor is so strong.
Identification
There are three stages of creosote buildup in a chimney, but all three stages can be dangerous and are equally flammable. The first is a flaky buildup, but this can be removed with a chimney brush because it is very loose. The second stage is a more tar-like buildup, and a scraper may be needed to remove it from the interior of the chimney. The third stage of creosote buildup normally occurs after a chimney fire has already occurred, and resembles black glossy candle wax.
Issues
Creosote not only smells like tar, it also has tar-like properties. It can become gummy or sticky, and be difficult to remove after a significant amount of it builds up, even with a chimney brush. Creosote is also extremely flammable, so a fire burning below in a fireplace may ignite the creosote that has built up in the chimney, starting a chimney fire. Chimney fires can be difficult to notice and can result in severe fire damage to a home.
Prevention
Creosote should not be allowed to build up in a chimney. A creosote-free chimney helps to prevent chimney fires and the strong odor of creosote in your home. Your chimney should be cleaned thoroughly by a professional at least once per year, or twice per year if you use your chimney heavily during the winter months.