DIY: Plans for Efficient Wood-Burning Built-In Fireplaces

Firebox

• 1

  Sketch out the dimensions of the built-in fireplace on graph paper; large might look impressive, but it’s notoriously inefficient. Plan a smaller fireplace, no more than 36 inches wide and the same height, and around 18 inches deep with the flue centered above the fire; for the greatest efficiency, the depth of the firebox should be no more than half its width and height.

• 2

  Examine different materials for the fireplace; most will choose brick, but refractory clay, which you make up yourself, is more efficient, although you have to cast it yourself and then line the back of the firebox with fire brick -- don’t select a metal fire back, as it can warp over time and won’t reflect heat back efficiently.

• 3

  Draw the fireplace so that the sides of the firebox angle in toward the back, and that the rear of the firebox angles inward as it rises; whatever material you choose for the fireplace will be added after the structure has been roughed in with concrete blocks, joined together with mortar, and this will include the floor of the fireplace.

Throat

• 4

  Lay out the dimensions of the flue on the graph paper, above the fireplace. Design it so that the throat -- where the chimney begins above the fireplace -- is no more than 4 inches wide and lined up to the center line of the hearth.

• 5

  Draw a side elevation that allows you to show the smoke shelf, which will be above the fireplace, at the bottom rear of the throat; the throat should extend for at least 12 inches between the fireplace and the flue. Show a damper at the base of the throat to shut off the fireplace from the throat and flue to prevent heat loss when the fire isn’t burning; it should be on a hinge or flange to allow it to open 90 degrees.

• 6

  Design the fireplace so it can accommodate a pair of doors; these will prevent heat from the room vanishing up the chimney. Select ceramic glass doors for the greatest efficiency, although even those won’t be perfect.