Monday, October 3, 2016


Count Rumford:
Fired up over efficiency.
Would you believe that a conventional masonry fireplace actually wastes up to 95% of the heat  it produces? It’s true. A burning fire creates a very strong draft of air up the chimney. All that air being sucked out of your house is then replaced with cold air that infiltrates through cracks and crevices. The warmth you feel from the fire is mostly radiant heat—essentially, infrared heat from the firelight. So a roaring fire that seems to be warming your home is actually contributing a pitifully small amount of heat.

Few things in the home have evolved as slowly as the fireplace. In 1798, the English scientist Count Rumford developed the first theories for fireplace efficiency. In the subsequent 150 years, very little changed in fireplace design.
The tall, narrow proportions of the
Rumford fireplace (this is a modern day
example) didn't suit Modernist architects,
no matter how efficient it was.
(Contractor: Monterey Masonry,
Sheffield, Massachusetts.)

In fact, many fireplaces actually regressed in efficiency—modern architects didn’t like Rumford’s high, narrow, and shallow fireboxes, which didn’t fit in with postwar home styles. So they modified them to look more modern.  The results were fireplaces even less efficient than those of Rumford's day.

Still, there were some improvements during the twentieth century.  One of the earliest refinements was a metal jacket installed around the firebox that took in cold air near the floor, warmed it, and exhausted it through vents above the fireplace.  Although it was a simple idea, it made a big difference in efficiency.

In 1927, Heatilator introduced the manufactured steel
fireplace unit, now the standard of the housing industry.
This more contemporary Heatilator advertising image
shows how the units distributed warm air into the room.
Eventually, prefabricated metal fireplaces were developed that completely eliminated the use of masonry. In the late 1920s, Heatilator introduced the first "manufactured" fireplace built of steel; in later years the company pioneered a system that could be supplemented by fans and ductwork to distribute warmed air to other rooms. In 1954 one of Heatilator’s competitors, Majestic, patented an all-steel fireplace that could be installed directly against wood framing, making installation much simpler and cheaper.  The unit could be positioned anywhere in a room and didn’t require any special reinforcement or fireproofing.

In the last thirty years, improvements in fireplace efficiency have been even more dramatic, thanks in part to nationwide energy efficiency mandates based on those pioneered by California in 1978 under Governor Jerry Brown.

Modern fireplaces are required to have glass doors
and to take in combustion air from outside. Hence,
while efficiency is way up, sitting in front of a fireplace
nowadays is more like watching television.
Today, prefabricated metal fireplaces are the rule rather than the exception. One reason is that they can be installed for about one-third the cost of a masonry fireplace. They’ve also been continually refined for efficiency and good draft, properties that in masonry fireplaces had depended largely on the mason’s skill. Here are a sampling of the choices available in prefabricated fireplaces:

•  Standard single-sided fireplaces are available in a large range of sizes, from a firebox opening of about 30” wide all the way up to 48”.  When equipped with optional electric fans and ductwork, they’re about four times as efficient as a conventional, open-fronted masonry fireplace.  Because the glass doors somewhat restrict the view of the fire, the smaller-sized units are often raised off the floor for better visibility.

Down on the Corner: A popular type of
corner fireplace suited to modern interiors.
This one is by Majestic.
•  Corner units, which are open at the front and on one side, are often used in a modern setting.  However, these fireplaces, and the types that follow, generally will look out of place in a traditional style home.

•  Two-sided (see-through) fireplaces can be used as room dividers between  living/dining or bedroom/sitting areas.  In recent years they’ve also been used directly next to whirlpool baths, although the practicality of this location seems doubtful.

•  Cove or peninsula type units have glass on the two broad faces and one narrow face, and are also very useful as room dividers.   Bay-type units are open at the front and on both sides.

•  Island fireplaces have glass on all four sides and are entirely freestanding.  Of course, they’re still enclosed on top to hide the flue.  Don’t confuse these with the rocket-shaped fireplaces of the 1960s, though. They’re much more low-key.


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