Leopard geckos need a hot hide surface of 88–92°F (31–33°C), a warm side ambient of 80–85°F (27–29°C), and a cool side of 70–77°F (21–25°C). A thermostat is mandatory with any heat source. Overhead heat (halogen or DHP) is the preferred primary heat source; a UTH provides supplemental warmth for the warm hide. Nighttime temperatures can drop to 65–75°F in most homes without supplemental heat.
New to leopard geckos? Start with the full leopard gecko care guide before setting up the thermal layer. If you haven’t chosen your enclosure yet, read the enclosure setup guide first — tank size and footprint affect UTH sizing decisions.
Leopard Gecko Temperature Zones — The Four Numbers That Matter
Leopard geckos are ectotherms. They cannot generate their own body heat and rely entirely on their environment to regulate temperature, drive digestion, and support immune function. Without a correct gradient, metabolism slows and health deteriorates.
Here are the four zones you need:
| Zone | Temperature target | Purpose |
|---|---|---|
| Hot hide surface | 88–92°F (31–33°C) | Digestion, immune function, peak thermoregulation |
| Warm side ambient | 80–85°F (27–29°C) | General activity; gecko spends time outside hides here |
| Cool side | 70–77°F (21–25°C) | Thermoregulation downward; escape from heat |
| Nighttime floor (all zones) | 65–75°F (18–24°C) | Natural nightly drop; acceptable without supplemental heat |
The hot hide surface temperature — 88–92°F — is measured inside the warm hide at floor level. That is not the same as the warm-side air temperature. The air can sit at 82°F while the floor inside the hide is 90°F. Both readings matter, and they require separate measurement tools.
The gradient runs end-to-end. Your gecko moves the full length of the enclosure to self-regulate — retreating to the warm hide to reach peak temperature, moving to the cool end to come back down. Both ends matter equally.
Quick check: If your cool side is running warm or your hot hide is below 88°F, thermoregulation fails. Confirm both ends before your gecko goes in.
Why Leopard Geckos Need a Temperature Gradient (Not Just a Heat Source)
Thermoregulation is voluntary and continuous. Your gecko moves through the enclosure to hit different body temperature targets for different physiological states — warm when digesting, cooler when resting. The enclosure has to make that movement possible.
If the whole enclosure runs warm, the gecko overheats and has nowhere to cool down. Chronic heat stress leads to dehydration and, over time, organ damage. If the whole enclosure is cool, digestion stalls and immune function drops.
The easiest way to destroy a thermal gradient is to centre the under-tank heater. A centred UTH heats both ends roughly equally. Position it on one end only — that single decision creates the gradient automatically.
The cool side is not a problem to fix. It is a feature to protect.
Under-Tank Heater (UTH) — Setup, Sizing, and Placement
An under-tank heater is an adhesive heat mat that mounts on the outside of the enclosure floor. Most experienced keepers now use overhead heat (halogen lamp or DHP) as the primary heat source, with a UTH providing supplemental belly-level warmth for the warm hide. If you are starting without overhead heat, a UTH alone is workable — but treat it as the supplemental component of a complete system, not the long-term primary source.
Sizing: Cover 1/3 to 1/2 of the tank floor. Position it at one end only. Do not centre it.
Layout — what goes where:
| What goes outside the glass | What goes inside the enclosure directly above |
|---|---|
| UTH adhesive side mounted flat | Warm hide positioned over the UTH footprint |
| Rubber feet / spacers (use them) | Thermostat probe at floor level inside or near the warm hide |
| — | Substrate layer (keep it thin over the UTH) |
Most UTH units come with rubber feet or spacers. Use them. The small air gap between the mat and the surface it sits on prevents heat buildup underneath, which reduces fire risk.
Substrate and heat transfer: Every layer of material between the UTH and your gecko absorbs some heat. Tile and paper towel have minimal impact. Loose substrate at 1–2 inches of depth can pull the surface temperature down significantly. Whatever substrate you use, confirm the actual hot hide surface temperature with a probe thermometer after setup — do not assume the thermostat set point equals what the gecko is sitting on. For substrate selection, see the substrate guide.
Do not cover the UTH with insulation, thick foam, or heavy objects on the outside of the tank.
Thermostat — Why It Is Mandatory and How to Set It Up
Every UTH must be connected to a thermostat. Full stop.
Without regulation, heat mats run at full output and surface temperatures can exceed 120°F — hot enough to cause thermal burns on your gecko’s underside or start a fire. A thermostat keeps the UTH cycling on and off to maintain the set temperature.
How it works: Plug the UTH into the thermostat outlet. The thermostat’s probe reads the temperature at its placement point and switches the UTH on or off to hold your set point.
Thermostat type for a UTH: An on/off mat stat (sometimes called a mat thermostat or probe thermostat) is the entry-level option and works well here. Proportional or dimming thermostats are better suited to overhead heat sources like lamps and deep heat projectors.
Probe placement — the step most beginners get wrong:
- Correct: Place the probe inside the enclosure, at floor level, directly inside or immediately adjacent to the warm hide entrance. This reads the temperature your gecko actually experiences.
- Common mistake: Placing the probe under the glass, between the mat and the enclosure floor. Glass and substrate absorb a significant amount of heat, so the gecko’s floor surface is always cooler than this probe reads. To compensate, keepers who use this method have to set their thermostat to 95–98°F — and that creates a dangerously high set point if the probe shifts position or glass contact changes.
- Recommendation: Place the probe inside the enclosure at gecko level. Set the thermostat to 88–90°F. Verify the actual hot hide surface temperature with an independent temperature gun or second probe before the gecko goes in.
⚠️ Never run a heat mat without a thermostat. Even 30 minutes of unregulated output can push surface temperatures above 120°F — enough to cause contact burns.
The Warm Hide — Position, Function, and Temperature Target
The warm hide sits directly over the UTH footprint on the enclosure floor. The temperature inside it at floor level is the hot hide target: 88–92°F.
This is where your gecko retreats to reach peak thermal load while staying hidden and secure. Digestion runs here. A gecko that can only reach high temperatures out in the open — with no hide over the heat source — is under low-grade stress every time it needs to digest a meal.
Your thermostat probe belongs inside or immediately outside the warm hide entrance. That is the read point that matters.
On the “belly heat” claim: Some older care guides say UTH is required because leopard geckos absorb digestive heat specifically through their belly. Modern understanding is more accurate: geckos can absorb heat through any body surface. UTH is valued as warm-hide supplementation because it keeps the hide floor at a stable temperature while the gecko is inside, undisturbed, and hidden — not because of belly-specific conduction. The value is consistency and security. For hide sizing and material details, see the hide sizing guide.
Measuring Temperature — Tools, Placement, and What to Avoid
Digital probe thermometer: Best for continuous ambient monitoring. Place the probe tip at gecko height — one inside or near the warm hide, one on the cool side. These give you real-time readings you can check at any time.
Temperature gun (IR thermometer): Best for instant surface spot-checks. Point it at any surface — the hide floor, cool-side floor, water dish — for an immediate reading. It only captures a single moment, so it does not replace a continuous probe. Use it on setup day to confirm your baseline, then for weekly spot-checks.
Thermostat display: Shows the reading from the thermostat probe only. That is one point in the enclosure. Do not assume the thermostat display tells you the full gradient picture.
⚠️ Stick-on dial thermometers are not accurate enough. They measure ambient air at the adhesive spot and cannot read surface temperatures. They routinely read 10–20°F below the actual surface temperature inside a warm hide. Your setup can be dangerously overheated while the dial reads normal. If this is all you have, replace it before your gecko arrives.
Recommended monitoring setup: Digital probe thermometer on the warm side (probe at floor level inside the warm hide) + temperature gun for daily spot-checks. Two independent data points gives you real confidence.
Record your baseline readings on setup day before the gecko goes in. If temperatures drift later, you have something to compare against.
Nighttime Temperature — When to Let It Drop and When to Add Heat
A nightly temperature drop is healthy and expected — not a problem to prevent. Leopard geckos experience significant day-to-night variation in the wild, and captive animals benefit from that same rhythm.
In most homes (65–75°F at night), no supplemental nighttime heat is needed. The UTH can stay on or be left on a timer depending on ambient room temperature.
Intervention point: If your room consistently drops below 65°F at night, add heat.
What to use: A Ceramic Heat Emitter (CHE) on a separate thermostat. It produces heat without any visible light, which is exactly what you need at night.
Never use coloured night bulbs — red, blue, or purple. The old claim that reptiles cannot see these wavelengths is not accurate. Leopard geckos can perceive them, and light at night disrupts their sleep cycle and causes chronic stress over time.
CHE setup: mount on the enclosure lid, connect to a thermostat, set to maintain a floor temperature of 65–70°F. Check that it does not push the warm end above the daytime target.
Night drop = normal and healthy. Only intervene if your room drops below 65°F.
Cold room / seasonal note: Monitor nightly temps during seasonal transitions. A sudden cold snap can drop room temperatures faster than you expect. If your home is not climate-controlled, run checks again as the colder months begin.
Heat Source Options — UTH, Overhead Lamps, CHE, DHP
| Heat source | Best use case | Thermostat type needed | Beginner rating |
|---|---|---|---|
| Under-tank heater (UTH) | Supplemental warm hide / belly-level heat | On/off mat stat | ✅ Simple starting point |
| Ceramic Heat Emitter (CHE) | Supplemental ambient or nighttime heat | On/off or pulse thermostat | ✅ Good secondary option |
| Halogen / incandescent heat lamp | Daytime overhead basking; IR-A+B penetration | Dimming thermostat | ✅ Preferred primary for most setups; adds UVB/lighting decisions |
| Deep Heat Projector (DHP) | Overhead IR-B/C; lightless heat option | Dimming thermostat | ✅ Preferred primary; no light emission; more expensive |
| Heat rock | None — do not use | N/A | ❌ Banned |
Overhead heat (halogen lamp or DHP) is now the preferred primary heat source — it delivers infrared penetration, supports naturalistic basking behaviour, and pairs with a UTH for supplemental warm-hide heat. A UTH-only setup is a workable starting point for new keepers, but plan to add overhead heat as your setup matures. If you want to explore overhead heating or understand how it intersects with vitamin D3 synthesis, see the lighting and UVB guide and calcium and supplementation guide.
Heat rocks are not safe in any configuration. Uneven internal heat distribution and unreliable internal thermostats mean the contact surface can be far hotter than the sensor reads. They have caused serious burns and deaths in captive reptiles. No keeper setup makes them acceptable.
Ambient humidity: Target 30–40% ambient humidity in the enclosure. That is a separate measurement from the moist hide microclimate — those are two different things, and they require different management. For the moist hide, see the humidity and shedding guide.
Common Heating Mistakes and How to Fix Them
| Mistake | Why it happens | Fix |
|---|---|---|
| Hot hide won’t reach 88°F | UTH undersized; too much substrate over UTH; probe outside glass reads higher than actual gecko level | Spot-check with temperature gun; reduce substrate depth over UTH; move thermostat probe inside enclosure |
| Hot hide exceeds 95°F+ | Probe under glass reads below actual surface; no thermostat at all | Move probe inside enclosure at gecko level; lower set point |
| Cool side runs as warm as the warm side | UTH centred instead of on one end; room above 82°F | Reposition UTH to one end only; add ventilation or AC if room is chronically too warm |
| Both sides feel cold | UTH underpowered for enclosure; thermostat set too low; probe misplaced | Verify wattage; recheck set point against temperature gun reading; reposition probe |
| Gecko stays in one hide constantly | Temperature imbalance — always in cool hide = warm side too hot; always in warm hide = cool side too cold | Spot-check both ends with temperature gun; adjust thermostat accordingly |
| Visible burns on gecko’s underside | UTH running without thermostat; hide floor directly over UTH with no substrate buffer | Connect thermostat immediately; add a thin tile or substrate layer between UTH and hide floor; consult a herp vet |
If you see burns on your gecko’s underside, that is a veterinary emergency. Do not attempt wound care at home — contact a reptile vet.
Setup Checklist — Confirm Before Your Gecko Goes In
Work through this before opening the transport container. Every item is a thermal readiness gate. If any box is unchecked, the gecko does not go in yet.
- UTH installed under the warm end of the enclosure (1/3 to 1/2 of floor area, one end only)
- UTH connected to a thermostat — not plugged directly into mains power
- Thermostat probe placed inside the enclosure at floor level, inside or adjacent to the warm hide entrance
- Thermostat set point at 88–90°F
- Warm hide positioned directly above the UTH footprint
- Temperature gun reading of warm hide surface: 88–92°F ✅
- Cool side floor temperature: 70–77°F (confirmed with probe or temperature gun) ✅
- System running for a minimum of 4 hours before any gecko is placed inside
- Nighttime plan confirmed: room stays ≥65°F (no action needed) OR CHE installed and thermostat-controlled for supplemental heat
- Digital probe thermometer in place for ongoing ambient monitoring
FAQ
Do leopard geckos need a thermostat?
Yes — no exceptions. Any heat source without a thermostat is unsafe. Heat mats without regulation can reach 120°F+, causing burns or fire. An on/off mat stat is the minimum requirement for a UTH.
Where do I put the thermostat probe?
Inside the enclosure, at floor level, directly inside or immediately outside the warm hide entrance. That position reads the temperature your gecko actually experiences. Under the glass reads only the UTH output — the glass and substrate absorb significant heat before it reaches your gecko, so that reading is consistently too high.
What if my hot hide won’t reach 88°F?
First, check substrate depth. If there is more than an inch of loose substrate over the UTH, it may be absorbing too much heat. Reduce the substrate depth over the warm end and recheck with a temperature gun. If the reading still falls short, the UTH may be undersized for the enclosure — consider a larger mat or a secondary heat source.
Do leopard geckos need heat at night?
Not in most homes. If your room stays between 65–75°F at night, the natural drop is healthy and you do not need to add heat. Only intervene if the room drops below 65°F. Use a ceramic heat emitter on a thermostat — not a coloured bulb.
Can I use a heat lamp instead of a heat mat?
Yes. Overhead heat sources work well, and many experienced keepers prefer them as the primary method. For a first setup, a UTH is simpler to install and control. Any overhead heat source needs a thermostat. For full details on overhead options and their interaction with UVB and D3, see the lighting and UVB guide.
Why does my gecko only stay in the warm hide?
If the gecko rarely leaves the warm hide, the cool side may be too cold (below 70°F) — check it with a temperature gun. A gecko that avoids the warm hide entirely likely has the opposite problem: the warm side is too hot. Check both ends before assuming a behavioural issue.
This article is for general care guidance only and is not a substitute for advice from a qualified reptile veterinarian. If your leopard gecko shows signs of illness, thermal burns, or behavioural distress, consult a herp vet. ExoPetGuides is an educational resource, not a veterinary service.