The reason for chimney sweeping is simple. As wood burns, it gives off water vapor, volatile gases and soot. The gases rise to the chimney and cool as they get further from the fire. When the chimney is cool, the gases condense on its walls leaving a sticky, tar-like substance called creosote.
Creosote is the cause of chimney fires. It ignites easily, burns rapidly and is difficult to extinguish. Chimney sweeping knocks the creosote from chimney walls and should be done annually.
Cleaning your chimney is not a difficult job if you have the right tools.The most basic piece of equipment is the brush, usually made with stiff wire bristles to scrape off the creosote. You may be tempted to try other devices to sweep your chimney, but a professional brush is well worth the cost. The brushes get rid of the creosote without chipping or cracking the flue lining. Hardware stores sell chimney sweeping brushes or you can get them directly from a supplier. Be sure to specify the shape of the flue, whether square, round or rectangular, and its dimensions.
Most chimney brushes come with wire loops at the top and bottom so you can tie a rope the length of your chimney to one end and a ten or fifteen pound weight to the other end. If you prefer not to climb on the roof you can buy brushes that screw into fiberglass rods. The rods allow you to do all the work from below.
Besides your brush you will need drop cloths, goggles for eye protection, a respirator to keep soot out of your nose and mouth, a safety light, and a screwdriver for removing sheet metal screws and/or the damper panel. Choose a clear, dry day for the job and assemble all your equipment before you begin.
Start by looking up your chimney with a light. Remove the cotter pin that holds the damper in place and take out the damper. Handle it carefully since it has been repeatedly exposed to heat and may be brittle. For a wood stove, remove the stovepipe and take it outside to be cleaned later. Pull a paper bag over each end of the pipe to avoid getting soot all over the house. No matter what you are cleaning, it is advisable to cover your furniture with drop cloths for protection.
If you are sweeping with a fiberglass rod system attach the brush to one rod and press it into the chimney. Make a small hole in the drop cloth and slip the rod through the hole. Tape the drop cloth to the mouth of the chimney, then continue to push the brush up the chimney adding sections of rod until you have brushed the entire length. Pull the brush down, removing sections of rod. Repeat the procedure until you hear no creosote falling.
If you plan to sweep the chimney from the roof, tape a drop cloth securely over the mouth of the fireplace. Take a rope, brush and safety light with you to the roof. Once on the roof, inspect the chimney for soundness. Loose bricks a crumbling mortar should be repaired before the next heating season. If the chimney is secure, remove the rain cap, climb on top fo the chimney and straddle it. Look down the chimney with a flashlight. The rough brown crust on the walls is creosote. Lower the brush slowly into the chimney until it touches the bottom. Pull up the brush and lower it several times till you can hear no creosote falling. Inspect the walls of the chimney again; they should be smooth, clean and free from cracks.
Now wait for the soot to settle-about 1/2 hours. If you have a clean out for an outside chimney, clean it out. Inside, carefully remove the drop cloth from the front of the fireplace and scoop out the soot with a shovel. Brush down the walls of the fireplace or wood stove with a heavy wire brush. Even 1/10 inch of creosote can seriously affect the heating capacity of your wood burner. If you have a wood stove, clean the baffle and remove the ashes from the smoke shelf at the back of the chimney. Do not use your vacuüm cleaner for this job; the fine soot will burn out the motor unless it is an industrial machine.
Once you have cleaned up you are through if you are working on a fireplace. For a wood stove you still need to go outside and clean the stovepipe you have removed. Take off any dampers and run a brush through each section. Check the stovepipe for pinholes and burned out spots. Stovepipe only lasts about three years and should be replaced at the first sign of weakness. Fasten the stovepipe back to the stove with sheet metal screws.
Since chimney sweeping is dirty and somewhat dangerous, you can hire a professional to do the job for you.
Once your chimney is clean, keep it that way by burning seasoned hardwood. Green wood produces creosote more quickly. Avoid flash fires caused by newspaper, gift wrap and dry greenery. Chemical cleaners of the chimney are basically ineffective and are no substitute for thorough chimney sweeping.
Finally, if after all your precautions, you have a chimney fire, don't panic. Close off the damper to cut off the fire's air supply and smother the fire with rock salt of baking soda. Do not throw water on the fire because the temperature change will crack the bricks and cast iron. If you can get to the roof cover the chimney with a wet blanket to keep sparks off the roof. Dial your local fire department immediately.