Rumfordizing Brick by Brick
How to convert an energy-wasting fireplace to an efficient heater.
Synopsis: Rumford fireplaces are designed to project more heat into a room than a standard design. This article describes the process of converting a conventional fireplace by reshaping the firebox. A sidebar offers an account of the man who originated the design.
Most modern fireplaces don’t do a very good job. Many smoke so badly that they can’t be used, and almost none are efficient heaters. In fact, many of them draw more heat out of the house than they return, sucking in warm room air and sending it up the chimney. But it’s possible to convert one of these mere ornaments into a functioning and efficient fireplace. An American Tory named Benjamin Thompson, later called Count Rumford, demonstrated the relevant principles two centuries ago.
Rumford proved that the key to an efficient fireplace is a properly proportioned firebox, with important dimensions based on the width of the opening. Both the firebox’s depth (distance from opening to fireback) and the width of the fireback should each equal one-third the opening’s width. This makes for a shallow firebox with covings angled at a sharp 45° to reflect the fire’s radiant heat into the room. The fireback, which must be vertical to a height equal to one-third the opening’s width, begins to slope forward from that point to a small throat above the lintel. The sloping back reflects more heat, and the small throat results in a more forceful movement of air up the chimney. It also leaves room for the smokeshelf, a necessary feature where descending cool air and ascending hot air circulate to set up a strong draft.
Rumford’s workmen renovated so many smoking fuelwasters in England that a new word entered the language. His wealthy customers didn’t just have their fireplaces improved, they…