What Is a Rumford Fireplace Anyway?
by Jim Buckley
(An article published the Spring, 1989 issue of the BOCA Official magazine)
At the BOCA Mid-Winter Meeting in Williamsburg the Building Code Changes Committee approved a change (B245-89)* which would permit the construction of Rumford fireplaces. Many building officials, especially those on the East Coast, know what Rumfords are, but by far the most typical comment heard was "What is a Rumford fireplace anyway?"
Count Rumford, for whom the fireplace is named, was born Benjamin Thompson in Woburn, Massachusets in 1753 and, because he was a loyalist, he left with the British in 1776. He spent much of his life as a British emissary to Bavaria where he received his title, Count Rumford. Rumford is known primarily for the work he did on the nature of heat.
Later in life, back in England, Rumford applied his knowledge of heat to the improvement of fireplaces. He made them smaller and shallower so they would radiate better. And he streamlined the throat, or in his words "rounded off the breast" so as to "remove those local hindrances which forcibly prevent the smoke from following its natural tendency to go up the chimney..." Rumford wrote two papers detailing his improvements on fireplaces in 1795 and in1798.** He was well known and widely read in his lifetime and almost immediately in the 1790's his "Rumford fireplace" became state of the art worldwide and remained so until wood-burning fireplaces more or less went out of fashion (in favor of coal and later gas fireplaces) in the 1850s.
There are many original Rumford style fireplaces in pre-1850 homes in this country. For example, Thomas Jefferson had Rumford fireplaces built at Monticello and the President of William and Mary College in Williamsburg had his fireplaces "Rumfordized" in 1824. George Renick, who introduced short horn cattle to Ohio in the 1790s and who built a fine house in Chillicothe (under construction from 1794 until 1804) started with an old-style fireplace with a cast iron fireback, but changed his plans as soon as he read Rumford and built Rumford fireplaces in the rest of the house.
Today, with the extensive restoration of old and historic houses and the renewed popularity of early American architecture in new construction, Rumford fireplaces are enjoying something of a comeback. Rumford fireplaces are generally appreciated for their tall classic elegance and their heating efficiency.
The problem is that when the BOCA Code was originally written in the late 1940s, builders had mostly forgotten about Rumford fireplaces. Central heating was common and fuel was cheap and the code writers of the 1940s and 50s, while interested in safety, were not concerned with fireplace efficiency. Besides, the ranch-style house was becoming popular and everything from ceilings to fireplaces took on a low, horizontal look. The modern fireplace prescribed in the BOCA Code is low and deep with a large throat. It doesn't heat very well. In fact it may be negatively efficient because it sucks out so much heated room air, but it usually doesn't smoke and it is pretty safe.
Change B245-89 that the Committee approved in Williamsburg doesn't reduce any of the safety-related standards. Fireboxes still must be at least 8" thick and kept 4" from combustibles, flues and smoke chambers must be lined and hearth extensions must be 16" or 20" deep.*** What would now be permitted are "prescriptive" or "design" standards that would specifically permit the construction of Rumford fireplaces as an alternative to the "prescriptive" or "design" standards which now permit the construction of the modern fireplace, but inadvertently prevent the construction of Rumfords.
Specifically, the BOCA Code now requires all masonry fireplaces to be at least 20" deep even though this is not thought to be a safety related standard. But a Rumford fireplace is supposed to be shallow (only one third as deep as it is wide) so this standard effectively prohibits the construction of Rumfords. The proposed change would allow Rumford fireplaces to be as shallow as 12".
The code also now requires that "the minimal cross-sectional area of the fireplace (throat) shall equal the cross-sectional area of the chimney connection." But in the Rumford fireplace, the throat is designed to function as a venturi and must necessarily be smaller than the flue - just as the nozzle on a hose is smaller than the hose that feeds it or the throat of a carburetor is smaller than the intake manifold. The proposed change would permit the throat of a Rumford fireplace to be smaller than the flue and as small as 1/20th of the cross-sectional area of the fireplace opening.
Philosophically, the BOCA Code is not supposed to be a design aid, and certainly, if a builder didn't already know how to build a fireplace, he couldn't rely on the little bit of design information now contained in the Code to build one that worked. Similarly, the proposed new language specifically permitting the construction of Rumford fireplaces won't guarantee success for a builder who hasn't studied how to build a Rumford fireplace. The drawings which accompany this article include a modern adaptation of Rumford's own drawings made almost 200 years ago. There are other versions of Rumford fireplaces and a number of books and articles on the subject. The objective of the Code change is not to favor one version over another but to modify the Code so as to permit any of these attractive and effective Rumford fireplaces which comply with all of the safety related standards in the Code.
*Text of Code Change No. B245-89:
Add new section to read as shown:** The Collected Works of Count Rumford, Volume II, Ed. by Sanford Brown, Harvard, 1969.
2402.1.1 Rumford fireplaces: Rumford fireplaces shall be permitted provided that the depth of the fireplace be at least 12 inches (205mm) and at least one-third of the width of the fireplace opening, and that the throat be at least 12 inches (305mm) above the lintel and be at least 1/20th the cross-sectional area of the fireplace opening.
*** Section 2402.1
Note: Proposal B245-89 was challenged but was approved later in 1989 at the BOCA membership meeting and was printed for the first time in the 1990 BOCA Code.
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