Firebricks inside a wood stove are used to keep the hottest portion of the fire from the exterior metal box. When these bricks begin to disintegrate, damage can occur to the metal box in the form of metal fatigue and warping. Firebricks that have small cracks in them will still perform the task of keeping high heat from the exterior sides of the wood burner. Replacement bricks must be of the same type and size as the originals and can be obtained from the wood burner manufacturer.
Allow the wood stove or wood burner to cool down from any previous fire. The wood stove must be cold to the touch. Firebricks, regardless of condition, can retain heat for several hours after the fire has died out.
Remove all wood ashes and other debris from the interior of the wood burner. Pull the upper retaining angle iron for the firebrick from the side of the wood burner. Use the screwdriver and adjustable wrench to remove the screws and nuts that hold the angle iron to the interior metal walls.
Pull the old firebrick from inside the stove. Use the vacuum cleaner and thoroughly vacuum out all sides of the firebrick area to remove any small particles that can impede proper placement of the brick.
Begin at the rear of the stove, and place the brick in the same orientation as it was removed. Most, if not all, firebricks are manufactured in a rectangular shape. In most cases, the firebrick will stand vertically with the bottom of the brick standing on the lower fire grate of the wood burner. The upper portion of the brick will be held in place with the angle iron you removed in step 2.
Install the retaining angle iron one piece at a time. Begin at the rear of the stove, and work your way to the sides of the wood burner. You may wish to install new bolts and nuts if the older hardware appears rusty or disintegrated. Check the alignment of the new bricks as you tighten the bolts in place for the angle iron.
Consult local fire regulations and insurance rules as some entities may require that a licensed technician perform this work. Not all firebricks are the same type. Check with the vendor you purchase the brick from to ensure it is rated for the type of fire you are burning. In other words, firebrick for gas combustion may not be of the same strength as that for wood fires. Wood burner firebricks normally do not require the application of any mortar. They are typically installed dry with no mortar holding them in place or together. The bricks do need room to expand and contract during heating and cooling. Mortar may cause some firebricks to prematurely fail. Follow the brick manufacturer's recommendations concerning mortar applications if applicable.