Synopsis: A Rumford fireplace is wide, tall, and shallow, with sides that angle in from the back and allow heat to radiate from the firebox. Mason Mike Mehaffey has adapted Rumford’s principles to modern aesthetics and code, building a firebox that is not shallow but still produces ripping fires that warm the space. In a series of step-by-step photographs, he explains how to lay the hearth, build and curve the back of the firebox, and then add the lintel and the damper.

Watch the companion video on building a Rumford-style fireplace.

In some parts of the country, a house isn’t considered a home unless it has a fireplace. A fireplace isn’t necessary for heating or cooking as it was just a couple centuries ago, but it’s still the centerpiece of many new homes, providing ambiance and, hopefully, supplemental heat. I say “hopefully” because some builders and designers don’t take into consideration that how a fireplace works is at least as important as how it looks.

As Sir Benjamin Thompson—better known as Count Rumford— realized in the late 1700s, most of the heat coming out of a fireplace isn’t dancing off the flames; it’s radiating from the firebox walls. To make the most of this, he designed a fireplace that’s wide, tall, and shallow, with sides that angle in toward the back to radiate heat out into the room. Prior fireplace designs—and many since—have sides that go straight back or angle only slightly, radiating heat toward each other rather than out into the room where it’s wanted.

The one knock against Rumford fireplaces is that the original versions were often so shallow that the fire very nearly spilled out into the room along with the heat. But the idea behind them does work for heating a room, and so people frequently ask me to build them.

I’ve adapted Rumford’s principles to modern aesthetics and code to build fireplaces that produce ripping fires that warm the space, but are also deep enough to assuage any concerns about safety. While the International Residential Code (IRC) has an exception for shallower Rumford-style fireplaces, my version is a hybrid based on the IRC’s standard firebox dimensions, which means it doesn’t require any special parts, and it won’t get any side-eye from code officials.

Lay the Hearth

When laying the hearth—the floor—of the firebox, work from the center out to help keep joints aligned. Code dictates how far the firebox must be from combustible materials based on the size of the firebox opening. This one is 42 in. wide and 42 in. tall.

Build the firebox

The key here is to keep everything symmetrical. Measure from the center out to make sure the sidewalls leave an equal exposure of the bricks in the hearth below.

Curve the back

The back walls of standard-depth fireboxes typically lean toward the front to carry the damper. Creating a curve provides an elegant, flared appearance.

Profile in curvage. Start off the curve slow, as the tilt of lower courses adds to those above it. If the curve starts to steep and then lessen, the joint between the back and sidewalls will appear as an S-shape. For beginners, building to a template can be handy.

Photos by Matthew Millham

More about fireplaces:

• Easy, Elegant Mantel – Creating a mantel has never been easier.
• Building an Efficient Fireplace – Using these practices to build your fireplace can help guarantee its success.
• Make a Prefab Fireplace Look Like It Belongs – If building a fireplace brick by brick isn’t for you, here’s how to make a factory-made fireplace look like it belongs.

From Fine Homebuilding #284

Watch the companion video on building a Rumford-style fireplace.