Proper Design for a Smoke-Free Fireplace

By James Dulley

Dear James: I am adding a room on to my house, and it will have a fireplace. The existing fireplace in the living room is often smoky. How can I keep the new fireplace from filling the room with smoke? — Jon C.

Dear Jon: Smoke from a wood-burning fireplace in a living room is, unfortunately, a very common problem. Once a room has filled with smoke from a fireplace, it is difficult to ever again 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 aesthetics in mind and little regard to how it will function (i.e., draw out smoke) and produce heat for the room.

In probably 95 percent of the cases of smoking fireplaces, the cause is improper design. 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.

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

The key fireplace dimensions that your builder should consider are the opening height and 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 an 18-inch depth.

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

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 an 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 a 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 relationship of the opening. It is most likely 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.

Send your questions to Here’s How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com.

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