Synopsis: A master mason explains how to build a fireplace that warms the room efficiently. He covers the whole project, from calculating the proportions of the firebox to shaping the smoke chamber and building a stone arch. A illustrated sidebar shows cross-section views of a properly designed firebox, smoke shelf, and damper.

A couple of years back, my good friend Nick called to tell me that he’d bought a 40-acre tract of land in southern Pennsylvania. I wondered how this purchase would involve me, and the answer came quickly. Nick planned to build a cabin overlooking the valley, and the centerpiece of the cabin would be a large stone fireplace. Having built hundreds of fireplaces as a mason, I was the right friend to call.

Finding stone wasn’t a problem. The mountainside lot had many old stone fences and loose rock strewn everywhere. Nick, however, wanted this stone fireplace not just for aesthetic reasons but also for heating the cabin. After discussing the options, we decided that our best bet was a Rumford-style fireplace, efficient due to its wide, high, shallow firebox.

Rumford fireplaces radiate heat

Count Rumford was a talented inventor who fled the colonies to England in 1776 because he was a Loyalist and supported the monarchy. Rumford was fascinated with fireplaces and chimneys. He experimented with the principles of fireplace design and construction, and he wrote a number of essays and opinions on the faulty fireplaces he observed. He built a reputation in England by repairing hundreds of faulty fireplaces.

In almost every case, Rumford discovered that the throat area of the fireplace was too large; throats tended to be large because there had to be enough room for a chimney sweep to climb through to clean the chimney. He discovered that a large throat made…