4 Reasons Fireplace Glass Doors Break (& How to Fix It)

A reader reached out and asked why their fireplace glass doors broke and if they should fix it themselves. While I haven’t had this happen personally, I did more research to find out more. Here’s what I found.

Fireplace glass doors break due to age, prolonged heat exposure, physical damage, and issues with quality or material. While prefabricated fireplaces have tempered glass doors, masonry fireplaces have ceramic glass doors and can withstand much higher heat. This is why ceramic doors can remain closed with a lit fire.

Let’s take a look at the 4 most common reasons fireplace glass doors break, why tempered and ceramic doors matter, and how we can fix them.

Need a fire starter for your fireplace? Check out these top-rated fire starters on Amazon.

1. Age

How Long Do Fireplace Glass Doors Last?

Fireplace glass doors typically last for 10+ years and even decades. However, every time a fire is burned that will slightly reduce the lifespan of the doors. That is because each time it is exposed to high heat, it reduces and weakens the strength of the glass door.

When the glass gets weakened, it becomes even more vulnerable to contraction and expansion from heating and cooling.

The lifetime of a fireplace’s glass doors largely depends on:

• Frequency of Fires
• Fire Temperatures
• Type of Glass (Tempered or Ceramic)
• Quality of Glass

Prefab fireplaces generally last about 20-30 years while masonry fireplaces can last well over 100 years.

Soot build-up and discoloration are common signs your glass doors are old and may need to be replaced. Cracks and scratches are other good indicators. This damage weakens the tempered glass and can lead to shattering later on.

If the glass doors appear like they were made decades ago, it is safe to assume that it is okay to replace them with something that has not had decades of exposure to fire.

2. Thermal Expansion

Most if not all glass doors are kept within a metal frame around the entrance of the firebox. As glass heats, it expands. Conversely, when it cools it shrinks.

If a fire becomes too hot or heats up too rapidly, it causes glass expansion that cannot be contained within the confines of its metal frame. If that happens, the glass may crack or shatter.

The typically safe temperature range for most tempered glass is between 400-500ºF. Anything in the 600ºF range and up could cause excessive thermal expansion, leading to shattered glass doors.

It’s recommended to leave tempered fireplace doors open while a fire is running (more on tempered vs ceramic doors later).

Recommended: When to Close Glass Doors on a Fireplace (The Truth)

If you’re still concerned about sparks or hot surfaces for pets or children, purchase a metal mesh screen as a replacement.

3. Physical Damage

Sometimes things break. Even though fireplace glass is tempered (strengthened against physical and heat damage), it is still possible to break it.

Accidents happen and there is no specific remedy to this except to make sure pets, kids, and heavy objects do not land near the glass doors.

Perform regular inspections of all fireplace elements, glass doors included, to ensure there are no:

• Cracks
• Scratches
• Chips
• Other signs of physical damage

A yearly inspection and cleaning are recommended for all fireplace components, including glass doors and the chimney or vent.

If you notice a small crack in a section of the glass screen, consider replacing it. A small crack is an indicator that the general integrity of the glass has been compromised, which could lead to the rest of the glass breaking, causing a later issue.

4. Tempered vs Ceramic Glass Doors

Prefabricated fireplaces require tempered glass while masonry fireplaces require ceramic glass. When a fire is running, tempered glass doors should not be closed, but ceramic glass doors can be closed if needed.

The quality and type of glass doors on a fireplace are large factors in their durability.

Tempered Glass Doors

Fireplace glass on prefabricated fireplaces is manufactured as tempered glass. This type of glass is typically heat resistant to about 400-500ºF.

When glass manufacturers create tempered glass, they heat the glass and then quickly cool it down. This makes it stronger than non-tempered types of glass, also known as annealed or untreated glass.

The tempering process causes the outer surfaces of the glass to compress and the inner surfaces of the glass to tense. Aside from increasing temperature and break resistance, this glass will also break into smaller pieces that stick together, instead of large sharp shards that could cause injury.

Tempered glass is the right choice if your fire stays between the 400-500ºF range. However, anything above that likely causes too much thermal expansion.

Ceramic Glass Doors

Another common form of glass for fireplaces and wood stoves is ceramic glass.

Ceramic glass looks like glass, but it’s actually a hardened ceramic material that is transparent.

This is not “glass” in the traditional sense, but rather is a composite of various oxide crystals in a silicon glass matrix.

Ceramic glass is significantly stronger and harder than tempered glass. Due to the closer proximity that wood stove fires have to their doors, and their much higher heat, ceramic glass is commonly used on these appliances.

Aside from strength and durability, the main difference between ceramic and tempered glass is that ceramic glass will break into chunks while tempered glass shatters.

Are Fireplace Glass Doors Safe?

Overall, fireplace glass doors are safe as long as you keep in mind the objects near a fire get hot. This includes rugs, furniture, and other possibly flammable or heat-sensitive objects.

Once the fire has died down, the glass doors can retain heat for about 45 minutes to an hour.

Even though fireplace glass doors are usually tempered, they still draw in heat and warm up. This also depends on how close the glass screen is to the fire as well as the size of the fire.

Some fireplace glass doors are removable and can be set further away from the firebox, whereas other types are built into the frame of the fireplace itself. 

Additionally, if you purchased a new set of glass screens, make sure all the plastic or styrofoam packaging is removed. It could be easy to accidentally burn the packaging and fill your house with an even more unpleasant type of smoke.

Recommended: 4 Ways to Keep Fireplace Smoke Out of the House

It’s best to keep your distance and only handle the glass screen from the handles/bars that allow you to maneuver it without physically touching the glass itself, at least until it has cooled down.

If you have kids or pets, it’s safer to use a fireplace or hearth screen in front of the fireplace. This way there’s an extra barrier between any jumping embers or hot surfaces.

If the fireplace glass breaks, another added safety benefit is that tempered glass will not shatter and spread. Instead, it shatters and generally maintains its form.

This appears as a spiderweb has spread throughout the glass. However, if there is additional physical damage after it shatters (like it falls over), then you could risk having glass shards spread around on your floor.

When to Close Fireplace Glass Doors

It’s recommended never to close tempered glass doors while a fire is running, while ceramic glass doors can be closed. This helps the fire retain heat (leading to a hotter and cleaner fire), and prevents embers and smoke from entering the house.

If you have a prefabricated fireplace (built in a factory), it most likely has tempered glass as ceramic glass doors are against code. If you have a masonry fireplace, it’ll most likely either be open or have ceramic glass.

How to Replace Fireplace Glass Doors

If you’re not comfortable upgrading or replacing your fireplace’s glass doors, I recommend hiring a professional. However, if you’d like to do it yourself, here’s a list of items and steps on how to replace it.

What You’ll Need

• Nut Driver
• Screwdriver
• Clamps
• Level
• Masonry Drill
• Drill Driver
• Fireplace Doors
• Masonry Screws

You can find many fireplace glass door replacements on Amazon, but make sure to check your fireplace’s manual to confirm it’s the correct size and model.

Steps to Replace or Upgrade Your Fireplace’s Glass Doors

1. Remove the old doors. Use a nut driver to loosen the few screws holding the doors in place.
2. Attach the door’s straps to the bottom of the door and hold the door in its expected position in the firebox. Use a pencil or marker to mark where the straps land on the base of the firebox.
3. Remove the doors again and use a masonry drill to drill holes on the marks.
4. Place the doors upright and align the straps over the holes in the masonry again. Clamp the doors in place and use a level to check the door is in the correct position.
5. Using a drill driver, secure the straps to the firebox.
6. Now that the doors are secured in the proper position, add, mark, and drill for the straps on the sides of the doors.
7. Using the drill driver, secure the rest of the straps into place.

If you’re more of a visual person, check out this video on replacing glass fireplace doors by This Old House.

Sources

• https://coopertownservices.com/time-change-out-prefabricated-chimney/
• https://www.brickandember.com/long-brick-fireplaces-last/
• https://www.dillmeierglass.com/news/what-it-means-to-temper-glass
• https://www.sciencedirect.com/topics/chemistry/glass-ceramic

Recommended

When to Close Glass Doors on a Fireplace (The Truth)