Learn About: Tempered Safety Glass

What is it? How is it made? And can we make custom sizes here at Fast Replacement Glass?

 Jan 21, 2019  Fast Replacement Glass News

Learn About Tempered Safety Glass


What is tempered glass?

Tempered safety glass is a high strength glass, 4 to 7 times stronger than regular glass, with a thermal shock rating of 400° F. This replacement glass is what we use in all of our prefab, zero clearance fireplaces doors and most masonry fireplace doors. 


How is tempered safety glass made?

Tempered safety glass starts as ordinary or “annealed” glass. It is cut to the desired size and has all sharp edges removed before it starts the tempering process. It cannot be cut after the tempering process because it will very likely shatter.

Then the glass is taken to a tempering oven where it is heated to a temperature of 600° C (or 1112° F). For the cooling process, the outer surface of the glass is exposed to high pressure blasts of air for a few short seconds in a procedure called ‘quenching.’ Because the outer surface is cooled much faster than the inner center of the glass, this creates a combination of tension from inside the glass and compression from the outside of the glass. This is what gives the glass its strength.

When tempered safety glass breaks, it shatters into safe, blunt chunks instead of splintering into harmful shards like ordinary, annealed glass.


How is tempered glass different from ceramic glass?

Ceramic glass has an amber tint to it while tempered glass can come in four different tints: clear, bronze, grey, and occasionally black.

Ceramic glass has a higher thermal shock rating, being able to endure temperatures over 1000° F. It is also the only fireplace glass than allow for the doors to be closed with a fire is burning.* But this glass can only be used with masonry fireplaces, as having closed doors on a zero clearance fireplace is a fire hazard. Factory made fireplaces are not made to withstand the high heat that will build up in the firebox if the doors are closed and can easily start a fire within the walls of your home.


Custom Tempered Glass

We are proud to offer custom made tempered glass here at Fast Replacement Glass for all your needs! We specialize in tempered glass panes that will fit your application, no matter what fireplace brand and stove model you have, cutting the heat resistant glass to the specifications you need! Our tempered glass is available in 3/16", 1/8", and 1/4" thickness, and in clear, bronze, and light grey smoked tint colors.

Our delivery is super quick, shipping within 2 to 3 days. We temper each piece and inspect for quality on a per order basis, so the extra wait is well worth it. This means that our tempered glass has better quality control for more strength and less breaks.


Some important things to remember about tempered glass:

  • Glass expands when heated! Please request your cut of glass to be at least 1/8" shy of the mounting surface. This measurement will allow for a safe thermal expansion. We cannot be held responsible for breaks due to improper calculations!
    • If your original tempered glass sheet is still intact and you are able to obtain all of the dimensions needed for your custom cut product, you may use the glass for measuring purposes. However, we highly recommend double checking your measurements against the mounting surface for 100% accuracy.
  • Metal screws and mounting hardware also expand when exposed to high temperatures! To avoid damage to your glass when your appliance is in use, please do not over-tighten hardware. We cannot be held responsible for breaks due to hardware that has been secured too firmly.
  • To minimize thermal shock, We recommend a clearance of at least 4 to 6 inches between glass surfaces and fireplace log grates.
  • Burning a fire with your glass doors closed generates extra heat. While tempered glass can tolerate high temperatures, this condition may be too extreme for the glass to handle.
    • Most fireplace door warranties with tempered safety glass will tell you NOT to burn the fire with the doors closed or the warranty is voided. The reason being that a large fire could potentially exceed the thermal shock limits of the tempered glass and crack or shatter it. We recommend enjoying a roaring fire with the doors open.
  • Tempered glass should NOT be installed on a fireplace insert or heating stove. These appliances produce temperatures greater than 400°F and can shatter tempered glass. If you have one of these appliances, you will need ceramic glass.

If you're not sure what type of application you have or what kind of glass you need, please give our experts a call at 1-888-986-1535.



Click to shop tempered glass on Fast Replacement Glass

Shop now for Tempered Safety Glass


Click and shop all the ceramic glass at Fast Replacement Glass

Shop now for Ceramic Glass

*The only time fireplace doors can be closed with a fire going is if it’s a masonry fireplace with ceramic glass doors, and the fire has died down to a smaller size. Then the doors should be closed slowly to allow the glass to get used to the temperature change.

Last updated on May 6th 2019.


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