Masonry Chimneys and Maintenance

Types of Chimneys

Fireplace inserts or hearth stoves: These types of solid fuel burning appliances should have the vent directly connected to the flue of the chimney. This "positive connection" is intended to reduce the creosote accumulation in the flue.

Factory-built metal chimneys: Factory-built metal chimneys specifically designed for use with a solid fuel heater are often called prefabricated, Class A, or all-fuel chimneys. If you plan to use or buy this kind of chimney, consider these points:

• Be sure the unit is tested and approved by a nationally recognized testing laboratory.
  
  
• Do not try to use a natural gas or fuel oil vent, well casing, stovepipe, or other material as a chimney. These materials are not designed to withstand the high temperatures produced by a woodburner.
  
  
• Use only the type of metal chimney specified by the manufacturer of your unit. There are several different types of metal chimneys for woodburners and some may not be suited for your unit.
  
  
• The installation of the chimney must be done exactly as the manufacturer recommends. Most prefabricated metal chimneys have a minimum of 2 inches of clearance to all combustible materials such as wood studs or joists and any type of insulation.

Chimney Maintenance

All chimneys (metal or masonry) require special care so smoke and flue gases are properly vented. Have your chimney inspected before each heating season.

You should also have it cleaned regularly to reduce creosote. Creosote accumulates in stovepipes and chimneys and may ignite unless it is removed periodically. Creosote is mainly caused by:

• Slow smoldering (smoky) fires.
  
  
• Cool surfaces (such as exterior chimneys).
  
  
• Burning unseasoned wood.

Creosote buildup varies with the type of fires you burn, heater design, draft and the type of chimney. A rule of thumb is to clean a chimney whenever there is more than 1/8-inch to 1/4-inch of creosote.

At the very least, you need to clean the chimney on an annual basis, before the start of the heating season. Your chimney may need to be cleaned more than once per year depending on your individual use. Chemical chimney cleaners are generally not effective in reducing creosote buildup.

Masonry chimneys should have a flue liner to help reduce the possibility of the masonry absorbing creosote. If the flue liner in your chimney is cracked or damaged, it may allow creosote to accumulate and heat to escape, increasing the chance for a chimney fire.

Before you hire someone to reline your chimney, consider these points:

• Has the relining product been tested and listed by a nationally recognized testing laboratory?
  
  
• Has the contractor/dealer who will install the liner been trained in this process and how long have they been installing this type of liner?
  
  
• Do local code authorities (such as your building or fire department) accept or approve the liner you choose?

Special Note of Caution

Only one appliance or heater should be vented into a single flue. If a solid fuel burning appliance is connected to a flue already used by another appliance, such as a water heater, serious problems may arise. Some of these are:

• Increased creosote accumulation
  
  
• The possible deterioration of the flue
  
  
• The blocking of a lower heater vent by creosote
  
  
• The flue may not be large enough to handle an extra heater and allow carbon monoxide (a dangerous gas) to drift back into your home