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I have a full size double-pane all-glass patio door that I'd like to put a hole in for an air conditioner exhaust hose. I plan to drill a hole with a glass drill bit and then use a carbide rod saw to saw out the 5" diameter hole. I realize this will be a pain in the butt but there are no other places in the apartment I can cut the hole.

How likely is this door (or one like it) to be made of tempered glass? It looks to be at least 10 years old. Not sure how common tempered glass is in these kinds of applications. The apartment isn't really well-built.

The glass is SGG Climalit. I can't find one shred of contact info on their web site to ask them, though it looks like they do offer tempered glass options. This is in Spain. https://www.climalit.es/

Glass logo Better view of door pane construction View of entire door

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    Even if it's not tempered, do you realize that it is a double-pane insulating window and cutting a hole in it will allow normal air in and defeat its purpose? It'll also get dirt and condensation inside which you'll never be able to clean.
    – brhans
    Jul 4, 2018 at 14:30
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    Large sheets of window glass are (almost?) always tempered, especially when used as a door. Jul 4, 2018 at 14:51
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    Yeah, don't cut a hole in your door. It's just a bad idea for several reasons. It is probably tempered.
    – isherwood
    Jul 4, 2018 at 14:59
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    1) You'll have moisture and dust inside the glass unit, making your door look perpetually filthy, and 2) it's probably tempered (being a door), and will explode when you try to cut it.
    – isherwood
    Jul 4, 2018 at 16:00
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    Yes it is tempered. Don’t drill a hole in it, it will explode the minute you manage to nick the surface. And I don’t believe you - there has to be another place to put a hole to the outside.
    – paul
    Jul 4, 2018 at 22:07

4 Answers 4

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Since you clearly are not interested in advise on how to accomplish your task and you only want to know if your glass door is tempered or not AND since we can not answer this question for you then here is a test you can perform.

Step 1, - Cut a hole in the glass of your door.

Step 2, - After the glass breaks, look at the size of the pieces. If it shatters into a million little pieces it is tempered. If it breaks into larger jagged pieces and shards it is not tempered.

You can avoid steps 1 and 2 if you like and proceed directly to step 3 but this will result in you not knowing if your glass is tempered or not

Step 3, - Buy a new door with a half-length window and cut a hole in the non window section.

(This test is for entertainment proposes only, mostly mine although I am sure those who have been tersely rebuked by you for offering advice will probably get a kick out it. IF you do perform this test then I am not responsible for you breaking your glass, cutting yourself or feeling embarrassed for not taking advice offered.)

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Get a pair of polarized sunglasses and look at the window (as well as a car rear window for reference)

The strain pattern resulting from tempering can be observed with polarized light or by using a pair of polarizing sun glasses.

If it is tempered, you will see a pattern like this:

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    I believe that will only tell you whether or not it is polarized glass or not but i am not sure.
    – Alaska Man
    Jul 4, 2018 at 19:19
  • I agree with Alaska man, however all auto glass is safety glass of one kind or another.+
    – Ed Beal
    Jul 4, 2018 at 19:25
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    Car windscreens are not tempered, just laminated, but all other windows are tempered. The polarization pattern is an intrinsic characteristic of the internal stresses in tempered glass, and I've updated my answer to reflect that.
    – flaviut
    Jul 4, 2018 at 20:03
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I would say it is 100% tempered glass if built to code, both the glass in the door and any next to the door are required to be tempered (I don't remember the distance from the door before non tempered is ok) . Added some code references: found a reference from the international building code, 2015 date, 2406.4.1 and 2406.4.2 swinging, sliding and bifold doors require safety glass, if I read it right glass within 24" of a door. Tried to copy and paste but could not do it on my phone , earlier in the article it did specify the type of marking and things like wire embedded , plastic layers like windshields or tempered are all acceptable.

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  • There's nothing code about this apartment. But be that as it may, do you have any suggestion on how to find out if this is tempered?
    – Maddix
    Jul 4, 2018 at 15:25
  • +1 For @JimStewart , Yes, it will shatter when you start drilling a hole if it’s tempered. In the U.S., there is a small engraved icon or numbers in the corner of the glass.
    – Lee Sam
    Jul 4, 2018 at 16:40
  • @JimStewart As I mentioned, this is in Spain, not the US. I also included the engraving in the photos.
    – Maddix
    Jul 4, 2018 at 17:09
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First, you almost certainly have tempered glass. There is the decal, and also it is required by code for safety reasons. As another person posted, "the international building code, 2015 date, 2406.4.1 and 2406.4.2 swinging, sliding and bifold doors require safety glass". So, yes, it is tempered glass.

Second, even if it was not tempered, it's double-glazed. If you cut a hole in it, the gasses will escape and you will lose all the insulation and sound properties from the glass.

Your best solution will be to cut a hole in the wall, not the glass. I am assuming you are not renting, because if you were, you would not be wanting to cut a hole in a sliding glass door that would then need to be replaced (by you). If you are willing to cut a hole in a sliding glass door, then you should be willing to have the better solution which is to cut a whole in the actual wall. Yes, the wall.

It is less of a project to cut a hole in the wall than to do what you're trying to do. It will also make the egress door not restricted from opening.


That all said, there are a few ways to tell if glass is tempered.

First, tempered glass has a decal stating such. Look around for the decal. If you find it, you have tempered glass.

"Every tempered glass sheet has stamped which is work like an identifier for tempered glass. This stamp shows manufacturer name and the CPSC standards, the stamp is a key symbol to give you a proof whether the glass is tempered or not." (Source)

If you do not find the decal, it still might be tempered but either you did not find the decal, or it was not put on, or it was hidden somehow. Or, it may not be tempered.

The second way is to look at the edges, if you can take the door apart. Tempered glass has smooth edges, while non-tempered glass has rough edges.

The third way is to use polarized glasses and look at the glass. "If you see darkened shady lines or spots spread across the glass surface, this is it. That glass is a toughened one. These lines are formed during the tempering process" (Source)

My own suggestion is speculation, but if you look at the glass under a microscope, it should look different, because the glass is under tension if it is tempered.

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  • Agree that cutting a hole in the wall will be easier than cutting the glass. However, the OP specifically states "apartment" which, in the US at least, strongly implies a rental. Neither option is really good for a renter. Also, this is nearly 4 years old, OP has probably moved on by now.
    – FreeMan
    Feb 23, 2022 at 15:12
  • You're right - since they are renting they should not be doing this - I would certainly be mad if my renter cut a hole in a sliding glass door. And, since it was years ago, I doubt OP is still renting there. They should not be destroying the place they are renting. If landlord does not provide suitable AC, this is illegal and they can move.
    – diy
    Feb 24, 2022 at 17:00
  • Interesting. I wonder where you live that air conditioning is required by law...
    – FreeMan
    Feb 24, 2022 at 17:04
  • Somewhere hot. You would actually die without AC in the summer. It's considered "unlivable conditions" and there is a landlord-tenant law that requires livable conditions.
    – diy
    Feb 24, 2022 at 23:25

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