To the inexperienced fireplace owner and operator, understanding the anatomy of their chimney system is complex. From the confusing terminology to the various venting systems, there is a lot to know. So, let’s start with the basics! This blog post will focus on answering this common question: What is a firebox in a fireplace?

Firebox vs Fireplace

It’s often a challenge to understand there is a difference between the fire-BOX and the fire-PLACE. The firebox is the open-to-the-room, inner section of the fireplace where you light and burn fires. 

As the name suggests, a firebox has a standard box-like shape. It features a flat base, three walls, and an opening at the front and top.

Since the fire burns inside of it, the walls and floor must be non-combustible. Typically, most consist of masonry materials such as refractory mortar, firebrick, or prefabricated metal material.

Masonry wood-burning firebox

Fireboxes play an integral role in a well-functioning chimney system. They keep the exterior walls and combustible wood beams safe from intense heat. They are also perfectly aligned with the flue liner, allowing smoke to travel safely up and out of the chimney’s flue.

Many get confused by the differences between a firebox vs. fireplace. The two are very similar but think of the fireplace as a general term for all the interior chimney components such as the damper, hearth, facing, mantel, and firebox. The box is simply one of the many components in the fireplace. They are intertwined in the same system, not separate from one another.

Types of Fireboxes

As mentioned earlier, the vast majority of homeowners own either a masonry or prefabricated firebox. It doesn’t matter if the fuel type is wood-burning, gas, electric, or pellet stove. All systems contain a box of some sort.

Traditional fireplace in office

Masonry Firebox

Masonry, gas, or wood fireplace fireboxes are constructed on-site by a skilled mason and consist of either stone, blocks, or bricks. These materials are bonded together with a unique, heat-resistant type of mortar called “refractory.” Of course, the three walls and floor consist of the same material to form a solid firebox of refractory panels. The back wall is slanted to assist in funneling the smoke up the flue. 

Building a masonry chimney is a massive project. It requires a significant amount of material and many hours of labor. So, it cost significantly more to install than a prefabricated unit; however, masonry construction is more durable and provides an authentic traditional look.

With annual maintenance by a certified chimney professional, your masonry firebox will successfully contain your family’s vibrant and cozy fires for a lifetime.

Traditionally, masonry is designed for wood-burning specifically; however, that’s not your only option. You can convert your masonry wood system to gas or even install a variety of beautiful firebox inserts for fireplaces directly into the opening.

Another excellent option for masonry is to invest in an outdoor fireplace firebox kit. Building an outdoor fireplace will transform the look and feel of your backyard!

Prefabricated firebox installation before and after

Prefab firebox and facing remodel

Prefabricated Firebox

A prefab fireplace firebox is a part of a factory-built unit assembled on the job site and installed in the chimney structure’s wood-framing. In addition to the box, a prefabricated system consists of a chase cover, cap, and pipe.

Both mason-built and prefab fireboxes are identical in shape and do the same things. Still, the most significant difference lies in the material. Prefabricated systems have either metal or refractory panels on the walls and floor. Like their brick and mortar counterparts, the prefab panels protect the exterior components from the fire’s heat output. These panels aren’t nearly as strong as masonry and will inevitably crack after excessive use and heat exposure.

Decorative Firebox

Decorative brick firebox panels are found in factory-built fireplaces. In lieu of the fire brick and mortar assembly fireboxes found in masonry systems, factory-built systems frequently feature a large ceramic panel that is textured in a way to simulate a faux brick pattern.

These panels, the floor, the back wall, each sidewall are all one piece. Though, from a distance, they appear to be individual bricks due to their texturing in the manufacturing process. 

As mentioned earlier, like firebrick, panels are manufactured to withstand tremendous heat and like firebrick, after enough fires or trauma, they will crack and begin to fall apart.

Gas logs in prefabricated firebox

Decorative gas logs

When replacing panels or firebox tiles for your fireplace, care must be taken to order any replacement parts, including the firebox panels from the manufacturer.

This ensures the parts you’re getting will fit and meet the UL specifications at the time it was manufactured. On occasion, manufacturers offer a variety of panel styles for a particular model of fireplace. Consult the manufacturer’s website and brochures for different decorative options, if available.

If you’re looking to beautify your firebox even further, then try utilizing the various stunning fire accessories available such as decorative logs, lava rocks, and fireglass.

Steel Firebox for Fireplace

Steel boxes were manufactured with the intent of being installed in a real brick chimney in lieu of a firebrick firebox. The hope was that having hollow cavities and ducts would allow the fire to heat up the small metal box on the outside. And through convection and the blowers, air would travel through the hollow walls and smoke chamber and exit out the sides of the brick fireplace.

While this design looked like a great idea on a blueprint, most steel boxes had to be replaced or thrown out because of eventual moisture-induced rusting.

How Long Does a Firebox Last?

With annual maintenance, cleanings, and repair investments, your masonry firebox will last forever. A prefab unit, however, is not designed to last forever. It varies from 10 to 30 years, depending on your usage, amount of maintenance, and if the technician installed it correctly. 

When it’s damaged or unsafe, many homeowners ask, “can you replace the firebox in a fireplace?” And the answer to that is a resounding yes! We’ll take a deeper look into this question in the next section.

Reasons Fireplaces Need Firebox Replacements

Prefab fireboxes need replacements because they protect the exterior combustibles. When refractory panels start to crack or rust, it exposes the combustibles to high heat from the fire. A cracked firebox in a fireplace constitutes a significant fire hazard and needs repair immediately.  

When a prefab system is well-maintained, it will last you a long time. But whether it be due to water leaks, excessively large fires, or natural aging, your fireplaces firebox panels will inevitably fail. 

With dangers of catching combustibles and your home on fire, cracks in your fireplace firebox should be taken seriously. That is why you need to schedule annual inspections with a certified chimney sweep!

If the damage to your box is minimal, the chimney technician will likely repair it. Of course, if it’s severe, the technician will suggest a complete replacement.

Masonry fireboxes are built to last a lifetime, but that doesn’t mean they’re immune to failure. Cracks can develop in the bricks or mortar joints. So, annual maintenance for masonry is equally essential!

Firebox Repair and Replacement Cost

Now to the ultimate question of, how much does a firebox cost? A new fire-box by itself costs around $500 on most retail websites. A new construction project for building a firebox for your fireplace will include a price increase to cover professional installation and labor fees. Minimal repair cost for damages such as cracking varies depending on the severity. 

Replacing the masonry costs thousands more than prefabricated because it requires abundant materials and extensive labor. Both types require trained expertise with knowledge of current NFPA safety codes

If you’re interested in a replacement, contact a certified chimney company to learn where to buy a firebox.

Herringbone fire brick pattern in prefab firebox

Picture above shows a prefabricated firebox with a faux herringbone fire brick pattern

Summary

The firebox is the central hub of your chimney system. It’s the open, box-shaped area where you light and burn the fires that not only keep you warm but also provide an immense amount of comfort and beauty for your home.

Every fireplace’s firebox is vital because they protect combustible material in the chimney from intense heat and help funnel smoke to the outside. Without it, authentic wood and gas fire experiences would be impossible to enjoy. Put your home in the best position for decades-long success by scheduling annual cleaning and maintenance by your local chimney professional.

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