Why Do Reptiles Need Heat?
Reptiles are cold-blooded animals; no, this doesn't mean they are mean and unfeeling. It means they have no internal generation of heat; they rely on their environment to thermoregulate and function properly. Cold-blooded animals have evolved for millions of years to thrive in their natural environments. This means they are what's called ectothermic animals. This is a group of animals consisting of reptiles, invertebrates, amphibians, and most fish that maintain homeostasis by absorbing heat from the environment. Because of this, it's our duty as stewards of their care to replicate their wild habitat. This requires countless hours of research to learn what the environmental parameters are needed for our reptile friends to thrive. The good news is that for all common species of reptiles, someone has done the hard work of figuring that out for you. All you have to do is learn them.
What is an environmental parameter, and what do you need to know? The environmental parameters are the measurable components of the environment, and what you need to know are the acceptable ranges for your chosen species. The two main parameters to monitor in most cases are humidity and temperature. Most other husbandry choices such as, enclosure type, substrate, and lighting, will be dedicated to maintain these parameters. Most reptiles require a temperature gradient, while others do fine with ambient temperature. Ambient temperature refers to the temperature of the air, or room temperature. This is best measured with a room thermometer. Temperature gradient will be used for reptiles that require a warm and cool side, and most often a basking spot as well. This will be used for reptiles that require a rise in temperature in order to do things like properly break down food. You will need to have thermometers on each end to make sure you have the appropriate range, as well as a means to measure the surface temperature of your basking spot. For humidity, it is mostly ambient and can be measured with a hydrometer that you can buy from any pet store and most big box stores, such as Walmart and Target. Some animals do well with a moist hide, which is a place to hide containing moist bedding allowing a place to go when extra humidity is needed and may only be used when shedding in some cases.
Pro Tips
Humidity doesn't mean moist. Trust your hydrometer. If you're having issues maintaining a high humidity, your answer is probably a change in substrate or cage type, rather than just wetting the enclosure.
If your basking temperature is just a few degrees high, getting a light stand to raise your basking light may be the easiest solution.
Cool side not cool enough? Your habitat is too small.
Placing a towel, tin foil, or foil tape over the cool side of a mesh top enclosure can help greatly in holding in humidity.
Peat moss can be bought at Home Depot or Lowe's and can be added to any substrate to help hold humidity.