Cast or welded stove parts deteriorate when exposed to high temperatures. Hot spots in the fire can warp and crack metal stove walls. The bottom of a metal stove can burn out and develop holes. Firebrick between the fire and the stove's metal parts evens out the heat and extends the stove's useful lifetime. An unlined metal stove also cools down quickly as the fire dies, but firebrick stores heat that helps keep a room's temperature steady.
Wood stoves rely on airtight construction to control the air feeding the fire and channel waste gases and smoke out of the house. Uneven heating causes different parts of the stove to expand at different rates. The stresses created by hot spots can permanently warp welded steel stoves or crack welded joints. In cast iron construction, cement and fireproof gaskets fill gaps between parts. Air leaks through faulty seals feed hot spots in the fire that can overheat and crack cast iron parts. Internal metal parts can be replaced, but damage to the outer case can ruin the wood stove.
Firebricks made of aluminous clay melt at 2,800 degrees Fahrenheit but remain stable at the temperatures inside a wood stove. Firebrick linings shield the metal walls of the stove from intense hot spots. As the firebricks heat, the warmth of the fire radiates evenly through the outer casing of the stove. Dense firebricks heat slowly and delay the stove's heat output, but firebricks cast from porous kaolin fireclay heat quickly and improve the stove's performance. Both kinds of firebrick extend the lifetime of metal parts. Lighter kaolin firebricks won't withstand as much heat as bricks made from denser fireclays.
Stoves lined with firebrick store more heat than plain metal stoves and radiate heat longer than all-metal construction. Stoves with firebrick liners also can withstand hotter fires than metal stoves and burn fuel more efficiently than a stove with hot and cold spots. Any metal stove benefits from a firebrick lining, according to the University of Missouri Extension. After many cycles of heating and cooling, firebrick cracks, but cracked bricks that stay in place work as well as intact bricks. When part of the brick crumbles, the brick needs replacing. Rebuilding a firebox can require refractory mortar as well.
Panels of natural soapstone add beauty to a stove's exterior and contribute some of the heating benefits of firebrick. Fires in a stove with soapstone panels heat with less tending, since the stove radiates heat from the soapstone long after the fire dies down. Soapstone stoves hold heat for hours longer than cast iron or steel stoves. Mounting a metal stove with a firebrick lining on a brick hearth and covering nearby walls with stone or brick can work as well as soapstone construction. The fireproof barriers store heat without delaying the stove's heat output, according to Woodheat.org.
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