Here's How: Smoke-Free Chimney Starts With Correct Design

Dear James: My fireplace does not draw well, and the room gets smoky sometimes. I am adding another fireplace. What construction tips are important so the flue draws better? -- Tyler F.

Dear Tyler: Your smoking wood-burning fireplace in your living room unfortunately is a very common problem. Once a room has filled with smoke from a fireplace, it is difficult to ever completely eliminate the smoky smell on humid days.

A large fireplace with an attractive hearth and mantel can be the focal point of a room, but hopefully not because it is belching out smoke. Too often, fireplaces are designed with only aesthetics in mind with little regard to how it will function to draw out smoke while producing adequate heat.

Improper design is generally the leading cause of poor draw and a smoky fireplace. There is a definite relationship among the various exterior and interior dimensions of a fireplace that must be conscientiously followed. If any one of them is off, the fireplace will probably not draw out the smoke properly. I would say this accounts for the problem 95% of the time.

In the other 5% of cases, there are external factors that cause the indoor smoking condition, even with proper design. These factors often relate to obstacles (trees, a neighbor's house, etc.) that create unusual wind patterns. These can produce a downdraft into the chimney that forces the smoke out indoors. Often a taller chimney can help, but not always.

The key fireplace dimensions that your builder should consider are the opening height, width and the depth of the firebox. For example, a fireplace with an opening width of 28 inches should have an opening height of 24 inches and a depth of 16 inches. One with an opening width of 48 inches should have a 32-inch width and a 18-inch depth.

The other critical dimensions are the rear width of the firebox (they should taper), its height, flue size and minimum chimney height. Your builder should have a table of all these relative dimensions.

If you need one, you can contact the Brick Industry Association in Reston, Virginia, for its technical notes on "Residential Fireplace Design" (Note No. 19) and "Residential Fireplaces - Details and Construction" (Note No. 19a).

There are also some other internal chimney dimensions that your builder should consider. These are the height from the fireplace base to the damper and the height from the damper to the start of the flue liner.

When building the chimney portion of the fireplace, make sure to use high-quality materials. Many homes burn to the ground each year due to chimney fires. Creosote builds up inside any chimney over time.

If this creosote catches on fire, it should be contained by a well-built chimney. An old or improperly built chimney can allow the fire to reach combustible materials and start the house on fire. If you burn a lot of fires, have the chimney cleaned and inspected annually.

To make your new fireplace a heat generator instead of an overall energy waster, build a outdoor combustion air inlet duct into the hearth, directly in front of the fireplace opening. This will keep it from drawing heated air out of the rest of your house when a fire is burning. It also reduces the chances of negative pressure that can draw the smoke back down into your room.

To reduce the smoke from your existing fireplace in your living room, check the height and width size relationship of the opening. Most likely, it is too tall for its width. This is not uncommon, because a tall opening often looks better, particularly on a smaller fireplace. Most sheet metal shops can make a steel plate that fits across the top of the fireplace opening to effectively reduce its height. Have it brass plated for an attractive appearance.

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Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, Ohio, 45244 or visit www.dulley.com. To find out more about James Dulley and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.