# Will a heat mat crack a glass viv?



## Gman1980

Ok, I would really like a no bull, straighforward answer here as I am becoming SERIOUSLY confused.

I bought a VIV for my new gecko 4 days ago which came with a 7W heat mat.

The VIV sits in almost like a frame so that there is space underneath for air and the glass is not in direct contact with the unit I have it sitting on.

I have had the heatmat taped to the bottom of the glass since I bought it with no problems. The mat is warm to touch, but by no means roasting. I have a thermometer on the floor of the viv directly above the heatmat and its sitting at a consistent 90F (Which Im advised is a perfect daytime floor temp for a leo)

I understand the physics of this, that if something roasting heats up a cold conductive surface such as glass it could crack. However, I dont believe for a second that this little 7W heat mat that is warm can crack a strengthened glass vivarium.

Could somebody please give me a simple,honest answer?:blowup:I sometimes feel that on these forums, about 1% of people are straight talking and know what they are on about, and then you get the other 99% who copy what other people say and simply repeat it to other people. How can a heat mat that seems incapable of reaching higher than 90F crack glass?


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## Simon M

I would say NO...............My glass tanks have heat mats on and have never cracked?

???????????????????????????


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## Ophexis

Simon M said:


> I would say NO...............My glass tanks have heat mats on and have never cracked?
> 
> ???????????????????????????


I agree, mine hasn't cracked yet and my heat mat is under the glass...


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## Gman1980

Thankyou to both of you! I dig it when people give an honest answer based on their own experience rather than jus copyin other folks opinions!

Thanks again!:notworthy:


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## Hardwicki

Sorry to contradict but prolongued contact to glass may cause it to crack. I had a 3ft x 2ft glass fish tank with the mat underneath on a stat and it eventually after several yrs did crack, but the tank was 2nd hand and maybe had flaws not visible to the naked eye. I'd say just keep a good eye on it.


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## salukisue

*salukisue*

YES THEY DO I have had ALL tanks crack that have been on heat pads for a while.If you dont want it to happen try fixing the heat pad on to a polystyrene tile or thick cardboard and tape it to the side of the tank inside it


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## Hardwicki

salukisue said:


> YES THEY DO I have had ALL tanks crack that have been on heat pads for a while.If you dont want it to happen try fixing the heat pad on to a polystyrene tile or thick cardboard and tape it to the side of the tank inside it


Salukisue is right, act with caution with glass. It seems to develop a weakness over time. I found the smallest knock to heated glass caused the crack to increase greatly. It may be because it is not toughened glass. Not sure. : victory:


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## paraman

Gman1980 said:


> Ok, I would really like a no bull, straighforward answer here as I am becoming SERIOUSLY confused.
> 
> I bought a VIV for my new gecko 4 days ago which came with a 7W heat mat.
> 
> The VIV sits in almost like a frame so that there is space underneath for air and the glass is not in direct contact with the unit I have it sitting on.
> 
> I have had the heatmat taped to the bottom of the glass since I bought it with no problems. The mat is warm to touch, but by no means roasting. I have a thermometer on the floor of the viv directly above the heatmat and its sitting at a consistent 90F (Which Im advised is a perfect daytime floor temp for a leo)
> 
> I understand the physics of this, that if something roasting heats up a cold conductive surface such as glass it could crack. However, I dont believe for a second that this little 7W heat mat that is warm can crack a strengthened glass vivarium.
> 
> Could somebody please give me a simple,honest answer?:blowup:I sometimes feel that on these forums, about 1% of people are straight talking and know what they are on about, and then you get the other 99% who copy what other people say and simply repeat it to other people. How can a heat mat that seems incapable of reaching higher than 90F crack glass?


Provided that there is an air gap between the mat and the glass it shouldnt be a problem.. you may have noticed that exoterras for example have "feet" that raise the glass a centimeter or so and that some mats are provided with rubber feet to put under the tank. If the tank is raised a bit then there is no chance of thermal blocking. If a mat does thermal block then it can get really hot and as the mat is usually at one end the glass cant take the stress of a hot section and a cool section and subsequently breaks.


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## rum&coke

I had a glass tank crack with a heat mat under it. So yeah it can happen.


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## Jeffers3

Heating glass up gradually like this will not cause it to crack - and with the temperatures you are talking about, thermal stress will not make it more likely to crack over time either.

Glass will crack when there is a sudden temperature change, which will cause one side of the glass to expand or contract quicker than the other. Think about a glass dish in an oven. You can leave it in there for hours and it will not be affected. If, however, you pour cold water onto it, it will shatter immediately. Glass can, in fact, be heated up to many hundreds of degrees celcius, but will be fine as long as it is heated and cooled smoothly and slowly.

So, unless your mat develops a fault, there should be no problems.


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## Adams Corns

2 of mine cracked due to te heat mat ,


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## rum&coke

Jeffers3 said:


> Heating glass up gradually like this will not cause it to crack - and with the temperatures you are talking about, thermal stress will not make it more likely to crack over time either.
> 
> Glass will crack when there is a sudden temperature change, which will cause one side of the glass to expand or contract quicker than the other. Think about a glass dish in an oven. You can leave it in there for hours and it will not be affected. If, however, you pour cold water onto it, it will shatter immediately. Glass can, in fact, be heated up to many hundreds of degrees celcius, but will be fine as long as it is heated and cooled smoothly and slowly.
> 
> So, unless your mat develops a fault, there should be no problems.


 
To be fair your right ,my tank cracked because the corn snake I kept in it tipped over its water bowl and I guess the water on the warm glass made the temp change suddenly.


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## Jeffers3

Are you sure the heat mat was responsible alone? A chip in the glass, or spilled water perhaps? Glass is very stable thermally.


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## ambyglam

exo terra heat mats are designed to be stuck to the glass.... however they do state on them that they should only be used on either exo terra tanks or they give you little feet to stick on other glass tanks so that there is an air gap between the heat mat and the table etc


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## Jeffers3

All the heat mats I've seen are coated with a plastic laminate layer. Even the most thermally stable polymers will melt before glass is even slightly affected. Most types of glass don't melt until they reach around 1500 C. the following is from a study on glass breakage (which shows that a heat mat would have to be malfunctioning badly, or the glass was damaged), unless there was a sudden sharp temp change:

The only probabilistically-based results concerning glass exposed to a uniform hot temperature come from the Building Research Institute (BRI) of Japan [6]. In that study, researchers used a large-scale high-temperature door-leakage testing apparatus that resembles a large muffle furnace. Only single-glazed, 3 mm thick window glass was studied. For this type of glass, however, enough tests were run so that a probability graph could be plotted. These researchers' results are presented in terms of a probability of glass breaking out, as a function of temperature rise above ambient. The figure below shows the results. 
​









The Gaussian fit that can correlate this data corresponds to a mean temperature rise of 340°C, and a standard deviation of 50°C.


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## paraman

Jeffers3 said:


> All the heat mats I've seen are coated with a plastic laminate layer. Even the most thermally stable polymers will melt before glass is even slightly affected. Most types of glass don't melt until they reach around 1500 C. the following is from a study on glass breakage (which shows that a heat mat would have to be malfunctioning badly, or the glass was damaged), unless there was a sudden sharp temp change:
> 
> The only probabilistically-based results concerning glass exposed to a uniform hot temperature come from the Building Research Institute (BRI) of Japan [6]. In that study, researchers used a large-scale high-temperature door-leakage testing apparatus that resembles a large muffle furnace. Only single-glazed, 3 mm thick window glass was studied. For this type of glass, however, enough tests were run so that a probability graph could be plotted. These researchers' results are presented in terms of a probability of glass breaking out, as a function of temperature rise above ambient. The figure below shows the results.​
> 
> image
> 
> The Gaussian fit that can correlate this data corresponds to a mean temperature rise of 340°C, and a standard deviation of 50°C.


I think that the problem emanates from the fact that the heating is _not_ uniform. Its common practice for a mat to cover only 1/3rd of the floor space therefore by definition one end is warmer than the other. If you factor in a thermally blocked mat the temperature differential can be substantial and I suspect that over a period of time the expansion and contraction differences although small may well be enough to eventually crack the glass, or as you say a badly malfunctioning mat, there have been a few threads where the mats have scorched wooden vivs.


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## cardinalgrom

Gman1980 said:


> Ok, I would really like a no bull, straighforward answer here as I am becoming SERIOUSLY confused.
> 
> I bought a VIV for my new gecko 4 days ago which came with a 7W heat mat.
> 
> The VIV sits in almost like a frame so that there is space underneath for air and the glass is not in direct contact with the unit I have it sitting on.
> 
> I have had the heatmat taped to the bottom of the glass since I bought it with no problems. The mat is warm to touch, but by no means roasting. I have a thermometer on the floor of the viv directly above the heatmat and its sitting at a consistent 90F (Which Im advised is a perfect daytime floor temp for a leo)
> 
> I understand the physics of this, that if something roasting heats up a cold conductive surface such as glass it could crack. However, I dont believe for a second that this little 7W heat mat that is warm can crack a strengthened glass vivarium.
> 
> Could somebody please give me a simple,honest answer?:blowup:I sometimes feel that on these forums, about 1% of people are straight talking and know what they are on about, and then you get the other 99% who copy what other people say and simply repeat it to other people. How can a heat mat that seems incapable of reaching higher than 90F crack glass?


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Answer
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