When, Why, and How to Keep Your Chimney Clean


by Marcus Pickett

There are 25,000 chimney fires in the U.S. each year, and nearly two-thirds can be attributed to a homeowner's failure to have the chimney cleaned. (The rest can be attributed to installation, construction, and design deficiencies.) You probably already know that you're supposed to have your chimney cleaned, but you may not know when, how, or why it's so important.

Hidden Dangers Lurking in Chimneys

By far, the biggest danger lurking in your chimney is creosote. This material is a by-product of wood-burning fires caused by smoke that rapidly cools down in the chimney. Once enough creosote builds up, it can ignite violently and cause some of the hottest and most destructive residential fires possible. Witnesses have been known to describe the fire's sound as "a low-flying jet."

Often, a small chimney fire will set the stage for a larger inferno. Small creosote deposits can flare up and cause damage to the lining of your chimney. This, in turn, lets cool attic air into your chimney, accelerating the rate of creosote build-up, which can set the stage for disaster. In fact, some chimney fires don't even start in the chimney, but with rotted wood in attic spaces adjacent to a cracked chimney.

Preventing Creosote Build-Up

No regimen for wood-burning fireplaces can eliminate the build up of creosote, and these steps are in no way a substitute for cleaning. Yet, these preventative measures can slow creosote formation and reduce the likelihood that your chimney will catch fire between cleanings.

  • Use only dry, properly seasoned wood. Unseasoned wood causes more smoke and lower temperatures to be produced, which is the exact recipe for creosote.
  • Creosote's need for lower temperatures means most of it is formed at the beginning of the fire. Avoid frequent but brief use of your fireplace.
  • You may have heard burning rock salt prevents creosote build-up. This is half true. Burning rock salt will loosen creosote, most often causing it to fall into the fire and burn up harmlessly. But damaged chimneys run the risk of this creosote falling into cracks and crevices - an incredibly dangerous possibility.
  • Don't cut off the air supply to make a fire last longer. This will give creosote more time and cooler temperatures in which to form. By the same token, when you're done with your fire, put it out as quickly and as completely as you can. Smoldering embers also create more smoke and lower temperatures.

The Frequency, Cost, and Time Associated with Chimney Cleaning

How often you should have your chimney cleaned really depends on how often you use your fireplace. If you only use your chimney once a week for a couple of hours at a time, you can probably go up to three years between cleaning service. For most homes, however, more regular use dictates annual cleaning. Heavy use may even require semiannual cleaning. The only sure way to know is to measure the creosote - a difficult prospect for some homeowners - to see if your flue is lined with creosote greater than 1/8-inch thick. If you haven't cleaned your chimney in a while, it's a safe bet that it's overdue.

If you're still not sure, the good news is a chimney inspection should cost only $50 to $100 and should answer virtually any question you have about your fireplace and chimney. Naturally, chimney cleaning is a bit more expensive with an average cost of $298, according to data collected from homeowners who actually hired a chimney sweep with ServiceMagic, the leading online resource connecting homeowners to home improvement contractors. The average cleaning takes about four hours, and if you're chimney sweep doesn't take at least one hour, you should be suspicious of the quality of the job.

-- Marcus Pickett is a senior home improvement writer with ServiceMagic.com. He has written more than 1200 articles on managing your home and home improvement trends.