There isn’t a simple rule of thumb on how often to clean your chimney, such as cleaning after 50 uses or one year. The problem is, creosote can form when wood is burned incompletely. A smoky fire without enough oxygen emits lots of unburned tar vapors that can condense inside the flue and stick to it, possibly leading to a chimney fire. You can reduce creosote buildup in your fireplace by providing adequate combustion air, which will encourage a hot, clean-burning fire.
To check for creosote yourself, first make sure there’s no downdraft from the chimney. If you feel an airflow, open a door or window on the same floor as the fireplace until the downdraft stops or reverses and air flows up (tape tissue to the fireplace opening and watch its movement). Then, while wearing goggles and a basic disposable dust mask, take a strong flashlight and your fireplace poker and scratch the black surface above the damper (smoke chamber). If the groove you scratch in the creosote is paper thin, no cleaning is needed. If it’s 1/8 in. thick, schedule a cleaning soon. If you have 1/4 in. of creosote, do not use the fireplace again until it is cleaned—a chimney fire could occur at any time.
To check for creosote, shine the light near the top of the firebox, in the smoke chamber and around the damper. And check the flue, too, especially on exterior chimneys, where creosote builds faster than on interior chimneys because of lower outside temperatures.
The easiest creosote to remove is the feather-light dull gray, brown or black soot. The next form is a black granular accumulation, removed fairly easily with a stiff chimney brush. The third type of creosote is a road tar–like coating that is much harder to remove even with stiff chimney brushes, scrapers or power rotary whips. The final (and most deadly) is a shiny, glaze-like coating on the flue that is virtually impossible to remove.
The job of the chimney sweep is to remove soot, blockages and built-up creosote from your chimney liner, firebox, smoke chamber and damper. This cleaning will help create a safer operation of your system during the heating system. It take only a small accumulation of creosote glazing to create the potential for a chimney fire. Creosote is a highly flammable substance that builds up inside your chimney or liner as a result of burning wood. The rate of accumulation can be higher if you practice poor burning practices or have a burning appliance or stove that is not working well. Different types of wood create different amounts of creosote when burned. Pine causes a rapid build-up of creosote and should be avoided as a regular source of wood. Creosote can also reduce the draw of the fireplace and reduce efficiency.
Please contact a local CSIA Certified Chimney Sweep ASAP if you’re experiencing one or more of these potentially dangerous issues:
- Smoke from your fireplace is entering your living space
- You believe you may have experienced a chimney fire
- You smell a strong odor coming from your fireplace
- You have witnessed flames coming from your chimney