If your fireplace or chimney emits an offensive odor, it could be due to creosote buildup. This flammable substance can penetrate masonry chimney walls and cause irreparable damage.

Creosote deposits accumulate when chimneys aren't routinely cleaned, reaching 1/4 inch when left to accumulate on their own. Inspection and cleaning should occur whenever this dangerous substance becomes an issue.

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1. Creosote Buildup

Every time you light a wood-burning fire, combustion byproducts like smoke, gases and carbon particles travel up the chimney and form into creosote tar-like substances as they cool, eventually building up over several seasons to form layers that can reach several inches thick clogging the chimney from venting smoke, as well as becoming highly flammable; excessive creosote buildup is one of the primary causes of chimney fires.

Regular cleaning removes the first level of creosote build-up in chimneys. This dusty sooty material is easy to eliminate using an inexpensive chimney brush.

Cool flue temperatures and overuse of wet wood cause large layers of creosote to accumulate in chimneys, making second-degree creosote harder to remove than stage 1. Featuring black tar-like flakes that appear as black spots on its surface, second degree creosote poses greater health hazards than stage 1 creosote and may damage chimney lining in extreme cases; specialized rotary tools may be required for effective chimney cleaning in such instances.

2. Water Damage

Though your chimney system has been carefully planned, designed, constructed and maintained, issues could still arise. Matthew Northcott from OFTEC discusses some of the more frequent issues and how they may be resolved in his series of articles on OFTEC's website.

One of the most widespread chimney issues is blocked flues, often due to creosote build-up or bird nests or broken dampers. When this happens, smoke and carbon monoxide enter back into the home through vents redirected back into it from outside.

Chimney sweeps use camera equipment to reveal any obstructions and can remove them with their brushes. A blocked chimney may also indicate damage to masonry; water leakage from leaky pipes can cause bricks to crumble and lead to further deterioration and expensive repairs, so installing a cap that keeps out moisture can prevent further damage to occur.

3. Animals in the Chimney

If a homeowner hears scratching or rustling noises at certain times of day or night, this could indicate they have an animal trapped inside their chimney. Most often this involves birds or small animals falling down the chimney by mistake and becoming stuck inside. Frantic scratching noises indicate this animal trying to exit its hiding spot within.

Homeowners should never attempt to remove animals that have taken refuge in their fireplace alone; rather they should seek professional assistance as it could prove both dangerous for themselves and the animal in question.

Raccoons who find their way into chimneys tend to use it as a den, usually for giving birth. If you try and scare it away, its mother might leave some babies behind if you try and scare her away too soon. Therefore, to protect its babies inside, the best thing you can do for a raccoon that has taken refuge there is ensure the damper remains closed - this should do just fine for both parties involved!

4. Flashing Leaks

Flashing leaks can occur if it is improperly installed and are a common source of chimney and roof leakage. Metal flashing seals water away from areas around chimneys, vent pipes and valleys where two different roof pitches meet - making flashing leaks one of the more costly chimney problems that may require costly roof repair costs to address.

Chimneys may leak water if their mortar has become cracked or crumbly, leading to mold accumulation and masonry deterioration, both of which pose serious health hazards.

Signs of chimney leakage include white streaks on its exterior - known as efflorescence - which indicates leakage. An efflorescence stain indicates the need for inspection, repair and sweeping services on your chimney.

Birds' nests, squirrels' nests, and twigs can quickly block a chimney if it lacks an effective full-width chimney cap, leading to overheating and carbon monoxide infiltration into your home. A proper chimney cap prevents debris from entering the chimney while simultaneously blocking smoke and toxic gases from exiting into your house from its output.