What Is a Firebox?
The firebox is the main chamber inside your fireplace where you actually burn the wood or gas. It contains the flames and directs the intense heat and smoke safely up into the chimney. You'll usually see it lined with special heat resistant bricks or thick metal panels to protect the rest of your house. The word simply combines fire and box to describe the square shape of early fireplace burning chambers. Builders started using the term in the 1800s when fireplaces moved from open stone hearths to enclosed brick designs.
Types of Fireboxes
Most homes have one of two main types of fireboxes. It helps to know which one you own so you can maintain it properly.
- Masonry fireboxes: These are built entirely out of brick and mortar by a skilled tradesperson. They're usually found in older homes. The builder uses special yellow or white firebricks that can handle extreme heat without cracking. These are very durable but require regular mortar touch ups.
- Prefabricated fireboxes: Also called factory built fireplaces, these are common in newer homes. They consist of a metal box installed inside a wooden frame. The inside is lined with molded panels that look like real brick. These panels protect the metal box from the fire. When these panels crack, you just order new ones and swap them out.
Why It Matters to You
Your firebox takes a lot of abuse. It handles temperatures well over 1000 degrees Fahrenheit. This extreme heat makes the materials expand and contract every time you build a fire. Over time, this constant movement can wear down the mortar or warp metal panels. A healthy firebox keeps the flames exactly where they belong. If the lining fails, stray sparks or extreme heat can reach the wooden framing behind your walls. This is a massive safety hazard. A damaged firebox can also cause problems with your Home Insurance if a home inspector flags it.
What to Watch For
You should look inside your fireplace with a flashlight at least once a year. Check the walls and the floor of the chamber.
- Cracks in the brick: Hairline cracks are normal. Cracks large enough to fit a dime are a problem.
- Crumbling mortar: If the gray paste between the bricks falls out when you touch it, you need repairs.
- Rust or warping: Factory built metal fireboxes can rust out or bend from too much heat.
- Loose panels: Sometimes the side or back walls shift out of place.
Repair Costs and Upkeep
You should hire a certified chimney sweep to clean and inspect your firebox every year. This is a great task to add to your checklist during Your First Year as a Homeowner. If they find damage, you'll need a mason or a fireplace technician to fix it.
Repair costs depend on the type of fireplace you have and how bad the damage is. Keep in mind that local labor rates make these ranges vary.
- Tuckpointing: Scraping out old mortar and adding new high heat paste usually costs 150 to 300 dollars.
- Metal panel replacement: Swapping out warped panels in a factory built fireplace runs 200 to 500 dollars per panel.
- Partial rebuild: Rebuilding just the back wall of a brick firebox costs 500 to 1000 dollars.
- Total rebuild: Tearing out and replacing the entire brick chamber can cost 1500 to 3000 dollars.
You can learn more about general budgeting for fixes in our guide on What Home Repairs Cost. Don't try to patch a firebox with regular concrete or caulk. Standard building materials will shatter or melt the first time you build a fire. You must always use special refractory cement and firebricks designed for extreme heat.
