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Controlled Combustion The design of the fireplace itself plays a big role in the level of satisfaction it provides. The internal features that produce efficient, smokeless combustion tend to be the same as those that produce reliable chimney venting and trouble-free operation. To help guide fireplace design, here is a simple rule of thumb that neatly summarizes a lot of expensive research: The more air a fireplace demands for normal operation, the more fussy and spillage-susceptible it will be. Open fireplaces are the worst because they consume huge amounts of air — much more than is needed for combustion — which cools the system, thereby reducing draft. If your clients insist on a traditional fireplace, make sure they also agree to equip it with tightly sealed doors. The more you control the combustion in the firebox, the higher the temperatures of the exhaust and the stronger the draft. If your client doesn’t want glass doors or much heat, direct them to a gas hearth. Do the same if the architect’s plans call for a hearth in an outside chase situated at the low eaves of a cathedral roof. If the clients cannot be convinced to relocate the fireplace more centrally, you will both probably be happier with a direct-vent gas fireplace. Several other alternatives to traditional masonry fireplaces are also available. Metal stoves and fireplaces that meet Environmental Protection Agency (EPA) rules for low smoke emissions are the most resistant to leaking smoke into the house because they create a reliable draft (Figure 5).

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Figure 5. The Delta prefabricated metal fireplace is one example of an EPA-certified controlled-combustion fireplace (International Chimney Co., 400 J.F. Kennedy, St. Jerome, Quebec, Canada J7Y 4B7;; 450/565-6336).

These appliances are equipped with internal baffles, firebox insulation, and strategically placed combustion air inlets, which produce a stable, clean-burning fire, even at low heat output settings. Don’t sacrifice performance for lower cost, however. Some cheap units are made out of lighter, thinner materials, and are often connected to lightweight air-cooled chimneys with flue diameters that are too small relative to the fireplace opening. All of these cost-saving elements hurt performance. For customers who insist on a real brick or stone fireplace, a masonry heater is a good option (Figure 6).

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Figure 6. Masonry heaters, with their enormous thermal mass, are designed to burn very hot, then store and slowly release heat. Although more expensive than prefabricated metal fireplaces, they provide a reliable high-performance wood-burning hearth.

Masonry heaters use rapid combustion and heat stored in their massive structure to achieve high efficiency and excellent resistance to spillage. Both types of appliances solve the smoky fireplace problem because they get hot and stay hot until the fire fades to a coal bed and goes out. Both types also produce net efficiencies of more than 60%, a welcome feature during a winter electrical power failure. In addition, high-quality prefabricated metal fireplaces are much less expensive than traditional masonry fireplaces — often less than half the cost, depending on the facade and mantel design (Figure 7).

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Figure 7. Metal fireplaces don’t have to look metallic. The masonry surround for this metal fireplace gives a traditional look along with predictable performance, at a savings over a site-built masonry fireplace.

Trained Installers

In the last 20 years, building science research has clearly shown how fireplaces behave in houses. These insights are now being promoted through professional training programs. When planning a traditional masonry fireplace or metal heater, or even a wood stove, use suppliers, installers, or masons who understand the pitfalls of outdated ideas and impractical designs. Fireplace suppliers and installers who are graduates of the Hearth Education Foundation courses (; 716/343-6524) have a better handle on the issues that concern builders than those who are untrained. If a masonry fireplace is required, use only qualified heater masons who are certified under the Masonry Heater Association professional training program (; 802/728-5896). John Gulland is a hearth consultant based in Ontario, Canada. He is author of The Fireplace in the House as a System.