How to Set Up a Thermal Gradient for Thermoregulation in Pet Reptiles

Close-Up Of Turtle In Tank
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Reptiles, amphibians, and other ectotherms use external heat sources in their environment to regulate their body temperatures. Ectothermic (also called poikilothermic) animals are often called "cold-blooded" which is a bit of a misnomer as they often maintain quite high body temperatures (sometimes higher than mammals). In the wild, ectotherms move around within their habitat (from sunlight to shade, or from above ground to burrows, for example) to regulate their body temperature. If they get too cool, their metabolism slows (and in conditions that are too hot or too cold, enter states of inactivity or hibernation).

Maintaining the appropriate temperature is vital to bodily functions such as digestion and brumation. When keeping ectothermic animals, it is important to provide the proper temperature conditions in order for the animal to grow and thrive.

For many reptiles, it is not simply a matter of providing a constant temperature, however. They require a thermal gradient or a range of temperatures from a high end to a low end. Thus, the animal can move to a higher temperature or lower temperature to suit its needs at any given time.

How to Set Up a Thermal Gradient

Simply stated, you provide a gradient by providing heat at one end of a terrarium or enclosure. Whether you use heat mats, basking lights, heat lamps, ceramic heating elements, or a combination of these, they should all be placed at one end of the tank. This produces a natural gradient where it is warmer at one end or the other.

In the example shown above, heating components would be placed at one end of the tank, producing higher temperatures at that end of the tank than at the low end, where no additional heat is provided. Please note this is a completely fictional example since the photo is of my hermit crab tank and the temperatures given are simple an example of ideals for a corn snake (not what I provide for my crabs!).

If you have a species that also requires UVA/UVB lighting, that the UV producing light is placed in the same area as the heat source. Sometimes the UV producing bulb will run the length of the terrarium, which is fine, as long as the bulb overlaps the basking spot/heating zone. This is to ensure that as your animal basks in the heat, it also gets to absorb UVB, which is what would happen naturally.

In the wild, most species experience a temperature drop at night, and this should also be considered. The temperature for most reptiles should be dropped at night to mimic natural conditions (check for your species for exact ranges). This usually means turning off some or all heaters, or switching to a lower wattage heat source at night.

Illustration of thermal gradient for terrariums
Illustration of thermal gradient for terrariums Lianne McLeod

What Heat Sources to Use

There is no simple answer to that question, as it depends on the species, your preferences, your equipment, and your home. There is no hard and fast rule as to which size heat mat or bulb will give you the gradient your reptile needs, either, as it depends on the ambient temperature and your set up (substrate choice and depth, etc.). It also depends on what sort of temperature drop your reptile can tolerate at night. It takes research as to how best to meet the needs of your reptile, as well as some experimentation with your equipment to reach the ideal set up.

Some examples of heat sources you can use in your terrarium are shown on the next few pages. Remember, any of these heat sources, alone or in combination, will be placed at the warm end of your terrarium.

Close-up Of Chameleons Under Illuminated Light Bulb
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Using Light Bulbs for Heating Terrariums

There is a wide variety of light bulbs that can be used for heating. Again, depending on how your terrarium is set up, you may need to experiment with wattage to get the correct temperatures. Also, keep in mind that bulbs that produce bright or white light cannot be used at night. Some options include

  • Basking Lamps - provide a tight beam of light, good for any species that thermoregulate by basking (many tropical and desert species). These are for daytime use only.
  • Nocturnal Infrared Heat Lamps (shown below) - these have reflectors to focus the heat into the terrarium, and they can be used 24 hours. Also good for nocturnal viewing as the light given off doesn't disturb sleep patterns.
  • Other daylight bulbs - give off different types of light as well as heat. Daytime use only.
  • Other nighttime bulbs (e.g. Nightlight Red Bulb by Zoo Med) - also provide heat and nighttime viewing while giving off little visible light so as not to disturb sleep.
  • Regular incandescent bulbs - these are best placed in special reflector hoods to direct and radiate the heat more effectively. Depending on the species you are housing, these may be perfectly adequate and more economical than specialty lighting. Daytime use only.

Photo courtesy Zoo Med Laboratories, Inc.

Zoo Med Laboratories RS-100 Nocturnal Infrared Heat Lamp
Zoo Med Laboratories Nocturnal Infrared Heat Lamp™ (RS-100) Photo © Zoo Med Laboratories, Inc. Used with Permission.

Ceramic Heat Emitters

Ceramic heat emitters look a bit like odd light bulbs, but they are actually very efficient heaters that give off no light so do not impact the light-dark cycle (and therefore can be used day or night). They give off intense heat and should only be used with special porcelain receptacles as they can melt normal plastic receptacles. There are special clamp on lamps available for use with ceramic heat emitters.

Ceramic heat emitters get very hot and must be shielded from your animals or serious burns could result. You also need to be careful about touching these heaters yourself when doing terrarium maintenance. Despite the intensity of the heat, the heat from these does not tend to radiate great lengths so may not be effective at heating large enclosures.

These can also be used with thermostats and rheostats.

Photo courtesy Zoo Med Laboratories, Inc.

Zoo Med Laboratories - CE-100 Ceramic Infrared Heat Emitter
Zoo Med Laboratories - Repticare™ Ceramic Infrared Heat Emitter (CE-100) Photo © Zoo Med Laboratories, Inc. Used with Permission.

Undertank Heat Mats

Undertank Heat Mats are low wattage heat mats that can be used under the tank as well as on the side of the tank. The ones shown here from Zoo Med have an adhesive backing and are applied right to the glass of the tank. If used under the tank, the tank must be raised on the rubber feet (provided) or some other arrangement to allow air to circulate under the tank and prevent overheating under the tank. These do have the disadvantage that once they are adhered to the tank, they cannot be removed and reused safely, so it makes cleaning and rearranging more difficult.

These mats come in a variety of sizes and wattages. There are guidelines on the packaging for the size of tank the mats are appropriate for heating. The heat achieved in your tank will depend on the ambient temperature and your set up (type and depth of substrate, for example). For tropical or basking species that need higher temperatures, these function best as a secondary (perhaps 24 hour) heat source, used in conjunction with an overhead heat source for basking. They can also be used with a thermostat or rheostat.

Photo courtesy Zoo Med Laboratories, Inc.

Undertank Heat Mat
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Other Heating Elements

Mercury vapor lights: these produce both UVA and UVB as well as heat from a single source. Some experts have expressed concern over the intensity of the UV rays produced by these and their long-term safety, while others have used them without apparent problems. It is prudent to make sure your reptile has shaded areas in the terrarium if you use these, but they do have the advantage of covering both heat and light needs in one fixture, and although expensive they tend to be longer lasting than UV fluorescent. They should only be used in ceramic sockets.

Heat Rocks: I do not recommend these, especially older models. In the past reptiles have been known to sustain serious burns and many experts recommend avoiding heat sources with which a reptile can have direct contact. They also are not as effective at heating the ambient environment as some other sources, and I think with safer and more natural options such as overhead heating, these are best avoided.

Heat Cables: these are a fairly new addition to the market and offer a flexible heating alternative, and can be used in the tank, under the tank, or in breeding racks. I would probably stick to using these outside the tank.

Close up of a Bearded Dragon. Mpumalanga, South Africa
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Safety for Your Reptile: Overheating and Fire Hazards

It is important to make sure proper temperatures are maintained at all times, as well as making sure your reptile cannot be burned by the heat source.

  • Invest in a good thermometer.
  • Regularly monitor the basking spot, warm side, and cool side of your terrarium to make sure the appropriate temperatures are consistently provided.
  • Provide the proper nighttime temperatures.
  • Make sure your reptile cannot contact or get too close to bulbs or ceramic heat emitters or serious burns could result.
  • Prevent overheating.
  • Ideally, invest is a thermostat, which measures the temperature in the tank and turns the heating equipment on or off as needed.
High Angle View Of Lizard In Cage
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Safety for Your Home: Avoiding Fire Hazards From Reptile Heat Sources

  • Make sure proper receptacles are used for bulbs and heaters. Use receptacles rated for the size/wattage of bulb you are using, and use ceramic receptacles (higher heat tolerance) if indicated.
  • Do not overload electrical circuits, power bars, or extension cords.
  • Make sure your terrarium is safe for the heating you are using. For example, do not set heat lamps on plastic screen tops, or the top will melt.
  • Make sure all flammable materials (e.g. artificial plants, other terrarium furnishings) are kept away from heat bulbs or emitters.
  • Make sure curtains, furniture, etc. are well away from heaters.
    Run electrical cords safely (not under furniture or rugs) and watch for overheating.
  • Raise terrariums off the surface of the stand if using undertank heating.