Why Does My Chimney Cap Plug Up?

Chimney Caps

• Most chimney caps include wire mesh around the opening. This mesh not only keeps pests out of your chimney but also acts as a spark arrester. The mesh must be large enough to allow for the flow of oxygen and let smoke escape the chimney. The mesh size is typically 3/4-inch but can be between 1/2-inch and 1-inch. In California and other dry areas prone to wildfires, the mesh is usually the smaller size to prevent the escape of larger bits of ash, which can cause fires. Mesh with smaller openings is more likely to become clogged with ash, soot and creosote.

Creosote

• Creosote is formed when wood that doesn’t burn effectively creates smoke that condenses in the chimney. The substance coats the walls of the chimney and can clog the wire mesh of your chimney cap. Excessive creosote causes your fireplace to perform poorly. You may have trouble lighting a fire and keeping it going, due to the reduction of oxygen to the fire. Your fire may not give off as much as heat as usual, and carbon monoxide and smoke might enter the house. Burning unseasoned wood or wood with a high moisture content contributes to the buildup of creosote.

Other Clogs

• In addition to the buildup of soot and creosote, the wire mesh of your chimney cap can become clogged with leaves and debris following high winds. Burning paper in the fireplace might cause ash to become trapped in the mesh. Winter storms can cause snow or ice to accumulate around the mesh, clogging it and preventing adequate air circulation to the fire.

Cleaning

• When the chimney cap mesh is clogged, the fireplace’s draft is reduced, causing poor circulation and poor performance. This can lead to chimney fires. To prevent this from happening, inspect the chimney cap regularly. If snow or ice has accumulated around the mesh, remove it, or wait for it to melt before building a fire. Check for leaves and debris clogging the mesh. If you can see daylight through the screen, the cap is clear. If not, soot and creosote have built up on the mesh. You can scrape this off with a wire brush. If there is creosote buildup on the chimney cap, there is most likely buildup within the chimney. To prevent chimney fires, have the interior of the chimney cleaned by a professional.