Tank setup

[The Serpent Merchant]

Good point about the cardboard hides.

However, I have to respectfully disagree with your first comment. If the probe is not under the tank but inside the tank (ex. on the bottom of the glass) the temperature will be different from the outside, underneath the tank. Also, with a heavy tank and a thick carpet, it would be touching the UTH - not a good idea.
There is a reason UTHs come with those little stickies to raise the tank.
Even if it were possible that a thermostat could prevent heat build up, which I don't agree with, it is much better to have air flow than risk it otherwise. Also not a smart idea to tell someone new to the hobby not to provide an air gap, when it could indeed be a fire hazard. At least that is my opinion.

Thermostat probes are supposed to be attached directly to the UTH on the outside of the cage, and will therefor keep the UTH at the temperature the thermostat is set to and not a degree higher. I agree with you that a cage shouldn't be placed on carpet regardless, but there really isn't any need for an air gap. Even at full power a UTH usually won't get above 150 F which is still well below the point of catching anything on fire. The only time a UTH is really at risk of setting something on fire is if it actually shorts out, and an air gap isn't going to change anything if that happens. Further do you really think a small air gap is going to make a huge difference? It will lower the UTH temp by 10-15 degrees max. It is just something they say to protect themselves in case of a lawsuit. According to Zoo-Med their UTH's don't require a thermostat to stay in safe ranges. I can tell you from first hand experience that they are straight up lying about that. I have seen them get up to 130+ much quicker than you would expect, but level off after that.

I wholeheartedly agree with you that it is smart to play it safe with people who are newer to the hobby. I have written many posts stating so, but this is one of those things that I can say 100% for sure that I know to be true. I have 8 cages currently running with no air gaps between them and those cages have 12" THG heat tape which can get a lot hotter than a pet store UTH. My thermostat keeps them all at 98.0 F (+/- 0.9 F as that is the accuracy of my thermostat) Even without that first hand experience I have done the math that shows that a small air gap has very little effect on UTH temperature.

Even with the thermostat probe placed inside the cage (which isn't advised as it isn't nearly as safe) the thermostat will still be turning the UTH on and off or reduce it's heat output regularly preventing any meaningful heat buildup under the cat ego occur. Do you really think the surface under the cage could get hot enough to start a fire without the inside of the cage getting hotter than 95 F and the thermostat cutting/reducing power to the UTH?

All in all if you want to have an air gap for your UTH go ahead, it won't cause any issues, but it won't save you from a catastrophe in the extremely rare case that it happens.