My clients often express frustration resolving their appreciation for the qualities of a traditional wood burning fireplace with their desire for a green-built home. Depending on how they are used, standard fireplaces can allow more heat to escape up the chimney than they contribute to the interior. Ironically, a fireplace design invented by a Bavarian Count in 1796 offers a traditional solution with blistering efficiency. Rumford’s design has been slowly rediscovered over the past twenty years in America. Here in New Mexico, Allegretti Architects incorporates the Rumford fireplace whenever possible.
The design differs from conventional fireplaces in its special geometry. Rumford found that by making the firebox shallower and by flaring the sides at a wide angle, significantly more heat would be reflected into the room. The opening of a Rumford fireplace is roughly square shaped. The additional height again provides better opportunity for heat to be radiated into the room before escaping up the chimney.
The diagram above shows some dimensions for a traditional Rumford fireplace with a few modifications to respond to current building codes. The overall depth of the firebox has been shown as 20” because this is what is required in most US locations. The fireplace will perform better if this dimension can be reduced by 4” or more. The throat size can also be impacted, so it will be necessary to consult with the local building inspectors. These unusual throat sizes may require a custom made damper. As an alternative, I like to use a chimney top damper which is operated with a chain that runs down the chimney into the firebox. One manufacturer makes available special dampers and other accessories for constructing a Rumford fireplace.
Interestingly, the tall and shallow designs of Count Rumford were specified by Thomas Jefferson for the fireplaces at Monticello. At the time, these fireplaces were only surpassed by the Franklin stove (yes, Benjamin Franklin). It’s curious why today’s architects specify these efficient fireplace proportions so infrequently.