As we’re reviewing options for our next fireplace, we were wondering what are all the different materials that are used in fireplaces. After all, we’d like a better understanding of how they manage the fire’s heat in case we need to repair or replace the fireplace in the future. So, what materials go into making fireplaces?
Fireplace interiors are made from bricks, stone, concrete, and metal. Fireplace surrounds and mantels can be made from many materials, including wood, tile, and decorative stone. Fireplace interiors need to be able to withstand material and thermal shock and be completely inflammable.
So, while these are the most common examples of the materials in fireplaces, what are some of the other options? Also, what are the different parts of the fireplace called, and do the materials make fireplaces generally safe to use? Let’s find out more.
The Materials Used To Make Fireplaces
Fireplaces are made from a selection of materials that have been tested for their ability to withstand two things: material shock and thermal shock.
Material shock is stress caused by is physical damage, like from an occasional log tumbling off the pile into the side. Thermal shock is stress caused by wide temperature swings, which can cause materials to expand and contract significantly.
The materials that are used to build fireplaces are:
- Cast iron
- Firebrick (not regular bricks!)
- Vermiculite panels
Concrete and stone are commonly used as decorative elements on the outside of the fireplace, such as the hearth, chimney, or surround.
Cast iron is used for fireplace accessories like grates or pokers. It’s also the traditional construction material of wood-burning stoves. Although cast iron is very hard-wearing and has great resistance to material shock, it’s less effective as an insulator. Because of this, the inside chamber of a wood-burning stove is lined with firebrick or vermiculite boards to increase resistance to thermal shock.
Various kinds of metal are used to make gas fireplaces, faux-fireplace inserts, and prefabricated fireplace units. Unlike masonry fireplaces and chimneys, which are built on-site at a house from scratch, prefabbed fireplaces are put together at a factory and sent out in a few easily attached parts. Although they are often the cheaper option, prefab fireplaces are much higher maintenance, don’t last as long, and can’t take as much heavy use as masonry. Their chimneys also tend to attract birds to build their nests there, and the accumulation of material in the chimney passageway can cause overheating or catch fire.
Normal red bricks are not used for a fireplace; they are too porous and would shatter from the heat. The bricks that line the inside of fireplaces are cleverly named firebricks, and firebricks are made from the even more appropriately named fireclay.
Fireclay is a mixture of aluminum oxide, silica, and oxides of calcium, magnesium, iron, potassium, and titanium. All of these are naturally heat-resistant minerals. Raw fireclay is molded and baked in a kiln at a high temperature for a long period. The resulting bricks are great insulators, which means that they can absorb and reflect the heat of the flames without being physically affected.
Vermiculite is a naturally occurring form of silica and is combined with inorganic compounds and pressed into a thin board that is fireproof and, lightweight, and compact. Vermiculite reflector panels are the most common in Europe, but they also take advantage of silica’s great heat resistance and durability. These panels are used not just in fireplaces, but for several other fire safety applications.
What Are the Parts of a Fireplace Called?
A fireplace is made of many different parts, but here is a quick rundown:
- Firebox: where the fire burns. It’s usually rectangular or rhomboid, and its firebrick-lined sides reflect heat back into the room. The fire can be built directly on the floor of the firebox, or where a cast-iron grate can be positioned to hold logs.
- Hearth: the bottom of the firebox. This ledge extends outwards into the room and acts as a buffer between the firebox and the floor.
- Face: non-combustible material surrounding the opening of the fireplace.
- Surround: the area around the opening of the fireplace. It is sometimes referred to with the face but usually has a highly decorative element. Often topped with a mantel.
- Throat: the opening above the firebox where smoke enters the chimney.
- Damper: a metal door places in the throat that is used to seal off the fireplace from the outdoors when not in use. But remember to open it when you do start a fire!
- Smoke shelf: a ledge above the damper that keeps rain or soot falling onto the fire and prevents downdrafts.
- Flue: the vertical passage through with the smoke travels up and out of the house.
- Chimney: surrounds the flue to protect any flammable parts of the house as the smoke escapes.
- Chimney Cap: a metal cover for the top of the chimney that keeps out moisture, wind gusts, and animals (as well as their nests).
- Ash Pit: empty space below the fireplace where dead ash can be collected until it’s cleared away.
- Ash Dump: a small door in the bottom or side of the firebox where ash can be swept into the ash pit.
- Footing: the foundation of the fireplace, located below the ash pit. It’s made of heavy brick or cinderblock to bear the load of the fireplace and chimney. It’s also frequently found in the basement.
How Safe Are Fireplaces?
Fireplaces are safe as long as you take proper precautions and maintenance. Generally, the most important task is to have your fireplace inspected once a year. Also, having a fireplace screen will keep embers in and children and pets out. Keep furniture at least 3 feet away and a fire extinguisher close by.
A well-tended fire in a properly maintained fireplace is the best way to practice good fire safety. If you have dogs or small children, or if you’re worried about sparks breaking out over the hearth, installing a screen across the opening of the fireplace is an effective and easy safety measure.
Fireplaces and chimneys are also carefully constructed to prevent any sparks from escaping and starting a fire outside the house. Making sure chimneys are still working properly is a large reason why yearly inspections are so important.
That being said, some conditions like asthma can be worsened by the particles released in wood-burning fires. Additionally, using wood that is wet, diseased, or moldy can release toxins like creosote into your air. So it’s important to follow a few safety guidelines:
- Use local firewood: Wood from outside your area may be harboring pests like the emerald ash borer.
- Use firewood that has a moisture content of 20% and has been dried for at least 12 months. Wet wood releases more creosote, which can hang in your air or build up inside your chimney.
- Store your firewood off the ground and allow air to circulate around it. This helps to dry it out.
- Avoid all chemicals: including kerosene, gasoline, and charcoal starter. Never burn chemically treated wood or plywood in your fire.
- Check that your chimney cap is secured to the chimney.
- Check that your spark arrestor is undamaged and clear of any leaves or other debris.
- Remove tree limbs that are growing over the chimney opening.
- Clean out your fireplace so that ash doesn’t build up on the bottom. This allows better airflow and cleaner combustion.
- Stash a fire extinguisher nearby—and practice using it!
What’s Safer: Gas or Wood Fireplaces?
If you really like the aesthetic of a fireplace but are still hesitant to use one because of safety concerns, consider a gas fireplace.
Because they don’t burn wood, gas fireplaces are generally safer. With a gas fireplace, there’s no risk of sparks and fewer fumes and particulates affecting your indoor air quality. They also generate less heat, which can be convenient if you live in a warmer climate but still want to enjoy a fireplace.
Gas fireplaces can also be inserted into the opening already created by a regular open fireplace.
However, because they burn on natural gas (and on occasion—propane), their fuel costs are quite a bit higher than a wood fireplace, and it can be expensive to install a gas line. Although gas fireplaces don’t get as hot as wood, they do still create a good supply of heat, so it’s important to remember not to touch the glass doors that front a gas unit.
So, in our research, we learned that while fireplaces can be made up of a variety of different materials, they’re designed to achieve proper structural and heat resistance. If one of our fireplaces has an issue in the future, we’re now better equipped (at least a little bit) to fix it as we’re more familiar with the materials and their purposes.
If you’re interested in seeing how a brick fireplace is made, check out this video by Finehomebuilding.