Chimney cleaning: More than just a simple sweep

Why does my chimney need cleaning?

Every log you burn leaves traces of soot and tar, causing creosote to form (as droplets of tar condense on the chimney walls). The National Fire Code of Canada specifies that a buildup of more than 3 mm (1/8 in.) of creosote or soot particles on the walls of a chimney represents a potential fire hazard. Sweeping a chimney cleans it so that it can properly do its job of venting gases and smoke to the outside. 

Sweeping must be done at least once year, and it doesn’t matter how dry your firewood is: dry wood will produce creosote as well. Remember to choose the right species of fuel wood for best results. Hard, dense woods like maple and oak have high heat value. Others aren’t quite as energy-efficient, but will still do the job on cold days in the spring and fall. 

What to do in the event of a chimney fire?

If a chimney fire breaks out (i.e., the built-up creosote ignites) call the fire department immediately. A chimney rated at 2100°C in good condition should hold out, although the roar of the flames can be alarming. If the creosote burns off and leaves no apparent damage, have the building and chimney inspected regardless, before lighting the fireplace again. Repairs may be necessary.

Can I clean my chimney myself, or do I need to call in a professional?

No special technical skills are required to push and pull a chimney brush and clean out the creosote from a flue. You do need to be extremely thorough, however. And even if you clean out your chimney yourself, you must make sure that the many other components of the venting system are also carefully inspected and properly cleaned. This part of the job must be entrusted to a contractor with a RBQ licence for solid-fuel local heating systems. Have this person clean the venting system as well, at least every three years, if you do the chimney-sweeping part of the task yourself. 

A competent chimney sweep technician will inspect the condition of the heating appliance and all its components for damage:

• The chimney cap or crown;
• The caulking around the flashing;
• The interior of the stainless-steel duct or flue tiling; 
• Supports and connectors.

The technician will also check the condition of the pipe and “tee” connecting the appliance to the chimney, whether there is sufficient clearance for combustible materials, the operation of the damper and supply air duct, the quality of the firebricks, water infiltration, corrosion, cracks, perforations, bird’s nests, and more.

These periodic checks are essential to ensure the efficient and safe operation of your heating appliance. 

Do I also need to sweep the chimney of my oil-fired furnace?

Yes, you do! Your furnace’s heating efficiency—that is, its ability to properly burn all fuel—depends on how often you sweep the chimney and perform other furnace maintenance. Plus, the condition of the chimney directly affects its capacity to vent toxic gases and soot to the outside. Your best bet is to ask your oil-heat system technician at the time of your annual inspecting and cleaning. For gas-fired systems, no periodic servicing is required, unless specified by the manufacturer. 

Should sweeping be done in the spring or fall?

Chimney sweeping is best done as soon as the heating season ends, in the spring, when deposits are still dry and easier to remove. This will also give you enough time before the next season to repair or replace any damaged components. People in the house will be also be less exposed to unpleasant creosote odours during the work. Most homeowners, however, wait until the fall to have their chimney cleaned, and most companies canvass for customers at that time of year. If you love your fireplace so much that you heat your home with it daily during winter, you’ll need to schedule an extra sweep at mid-season—typically, once you’ve burned three or four cords of wood (also keep in mind that how often you need to sweep a wood-stove chimney depends not only on how much wood is burned, but also how you build your fires, which species of wood you use, and how wet the logs are).

If you’re burning more wood than you used to, tell your insurer

Insurers often set their premiums according to how many cords of wood are burned, so it’s very important to let them know if, for example, you decide to use your wood stove more often to save on your electric heating costs. 

How do I choose a chimney brush?

The chimney brush must be the right shape and size for your chimney. Polypropylene brushes are a popular choice for prefabricated chimneys or flue liners (both flexible and rigid), because they leave no corrosive metal deposits on the inner walls. There are also fine-wire-bristle brushes approved for these types of chimney, though, as well as a wide variety of other steel-bristle models for masonry chimneys. Be careful if you have a prefab chimney that includes any sharp angles (45° or more). Brushing too vigorously could damage the connectors.  

So-called chimney cleaning logs and similar products available on the market are in no way a substitute for proper sweeping with a brush. These products can create a false sense of security. They won’t detect structural problems, corrosion, or types of creosote. Different cleaning tools can be required depending on the type, or degree, of creosote involved: 1st-degree (dusty), 2nd-degree (flaky), or 3rd-degree (glazed). 

How do I do make sure I’m doing the job right?

• Vigorously brush all components of the exhaust system (chimney, connector pipes and smoke ducts), as often as is necessary. 
• If you have a newer-generation wood-heating appliance, remove the baffles to clean accumulated soot and ash. 
• Refer to the “Maintenance/Cleaning” section of the user’s manual.