High-Efficiency Fireplace for Your Home
The classic fireplace, with a blazing fire open to the room, is a traditional symbol of comfort and security. Many people include a fireplace among their “must have” features when planning for their dream home. On a more practical level, an open fireplace is notoriously inefficient as a means of heating a room. Its appetite for air, to keep smoke from the fire going up the chimney instead of out into the room, is what causes the inefficiency.
But lots of people, including many who already heat their homes with a woodstove, probably would consider a high-efficiency fireplace instead — if they could find one that would do the job efficiently. The enduring popularity of fireplaces combined with the choice many of us make to use renewable wood heat for our homes has prompted a number of changes in traditional fireplace design that attempt to address the inefficiency problem.
To be an effective heater, a fireplace must borrow some of the features perfected by woodstove designers over the last 20 years. These include gasketed, ceramic glass doors with an airwash system to keep them clean; firebox insulation and internal baffling. An adjustable combustion air supply also is needed to control the burn rate and, therefore, the output of heat.
Some fireplaces with all these features are on the market. The quick way to find them is to look for either factory-built fireplaces or fireplace inserts that are certified by the Environmental Protection Agency (EPA) as meeting the EPA smoke emission standards, which stipulate acceptable concentrations of air polluting emissions from freestanding woodstoves and fireplace inserts.
In designing these fireplaces to burn efficiently enough to meet the standards, the manufacturers have produced some beautiful units that also are able to provide significant heat to your home.
Here’s what you need to know to sift through the product specifications, sales advice and marketing hype to choose a unit that will match your personal heating and decor goals.
Open fireplaces commonly found in North American homes today fit into one of four general structural categories:
Conventional masonry.The standard traditional fireplace, this style is built of brick, block or stone by bricklayers following building code rules, without reference to any specific design criteria. It has a deep, squarish firebox that tends to trap radiant heat in the masonry and allow excess air to flush the heat up the chimney. The efficiency of all other fireplaces is compared to this most-common and least-efficient design.
Steel heat form.Popularly called heatilators (after a major manufacturer of this kind of fireplace), steel heat forms consist of a firebox and often a heat exchanger around which masonry fireplaces can be built.
Some steel heat forms have air circulation chambers, usually with inlets under the firebox at floor level and outlets between the mantel and the ceiling. When equipped with tight-fitting glass doors and a blower to force air from the room through the heat exchanger, these fireplaces can match the heating performance of an antique potbellied stove for short periods of time. But most heat forms are not designed for, and can’t stand up to, serious heating chores without failing. Commonly, the fireboxes will warp or crack from the fire’s heat.
Radiant fireplaces.The fireboxes of open fireplaces can be designed to increase the amount of radiant heat delivered to the room. Fireplace designs by Benjamin Thompson (aka Count Rumford) and later, Peter O. Rosin dominate this category. The Rumford design features a tall, shallow firebox with a narrow back and splayed sides to bring the fire forward and reflect more heat into the room. Rosin’s firebox, precast with a bulge in the back, reflects the heat down, towards the fire, and then out into the room. The success of both the Rosin and Rumford designs in directing more radiant heat into the room is apparent to anyone standing in front of one of these fireplaces. But neither design overcomes the problem of heat loss from the flow of air up the chimney. Nevertheless, they’re great options for a rustic weekend cabin.
“Zero-clearance” factory-built fireplaces.This style has a multi-layer sheet metal structure and usually, a firebox lined with custom firebricks. Around the firebox is a sealed space through which room air can circulate; an outer steel casing is insulated to moderate its temperature.
The name “zero clearance” refers to this style’s standard positioning against the combustible wood framing into which these units are built. Tens of thousands have been installed in suburban houses during the past 30 years. They mimic the look of conventional brick fireplaces but cost much less. The heating performance of conventional “zeros” is generally poor.View Source