The reason why it heats the air is because it heats the substrate, which then disperses the heat but it's only minimal. I'd imagine damp substrate will create more of an ambient air temperature. When used on the side, without anything to buffer the heat it will not heat the air but any objects near the mat, if you get me? Typically heat mats are used to create a hot spot where the animal will warm itself up. I wouldn't even listen to their instructions, as it doesn't emphasize enough in their instructions the importance of a thermostat! Habistat and pro rep are my favourite brands. I personally use it on the bottom with a thermostat and I have absolutely no problems with temperatures, as I've said heat mats can reach 100oF when unstatted but mine are always on a thermostat. They're not really amazing when used on the sides, unless you're using it for a arboreal animal that will seek it out for heat but a Horned frog won't really do that during the day, when it's in it's burrow. Heat lights work well but do tend to dry the tank, but in larger tanks a moisture gradient can be created.