Start with the actual room temperature
Many commonly kept tarantulas are comfortable across ordinary indoor temperatures in the low twenties Celsius. Species differ, and short natural fluctuations are normal. Check whether the room stays within the species range without prolonged cold or overheating.
Use a basic room thermometer if you are unsure. Measure where the enclosures actually sit, not beside a radiator or at the warmest point in the house.
The Tarantula Den rule: no heat mats on tarantula enclosures
We do not recommend heat mats for tarantulas. A mat can create a localised hot, dry area and the spider cannot always escape that gradient in a small enclosure. Heat mats are widely sold with exotic pets, but that does not make them a good default for tarantula husbandry.
If extra warmth is genuinely needed, heat the room more evenly rather than sticking a concentrated heater to the spider’s container.
What to do in a cold UK room
If a room regularly drops below the sensible range for your collection, improve the room temperature gradually. Central heating, a thermostatically controlled room heater positioned safely away from enclosures, or moving the collection to a more stable room are better approaches than heating individual boxes.
Any room heater must be used according to its safety instructions and should not blow hot air directly at enclosures. Monitor the whole room with a reliable thermometer.
Avoid overheating too
UK keepers often worry more about winter than summer, but direct sun through a window can overheat a small enclosure rapidly. Never place tarantulas where sunshine can turn the enclosure into a greenhouse. Radiators, hot PC exhausts and other local heat sources can create the same problem.
Stable is better than hot. A spider kept at a reasonable, steady room temperature is preferable to one experiencing a strong artificial gradient.
Temperature is only one part of husbandry
A correct temperature does not compensate for the wrong enclosure type, poor ventilation or inappropriate substrate moisture. Arboreal species still need airflow; fossorial species still need depth; dry-adapted terrestrials still should not be kept wet because the room is warm.
Check temperature alongside ventilation, substrate moisture and enclosure design.
When to check species-specific guidance
High-altitude, desert, tropical forest and temperate species do not all experience the same conditions. Use the species page for the broad practical range and origin, then adjust within that range based on the room and life stage.
Use the species temperature range and monitor the actual room; small daily and seasonal changes within that range are normal.
What about a dedicated spider room?
A collection room is easier to manage than dozens of individually heated enclosures. If you keep many tarantulas, monitor the room at several points and understand how temperatures change overnight and during cold weather. Shelves near ceilings, outside walls, windows and radiators can sit at noticeably different temperatures.
A room thermostat and sensible air circulation create a broad stable environment. Species with cooler or warmer preferences can then be positioned appropriately within that room without attaching heaters to individual boxes.
What about very small slings?
Tiny slings are more vulnerable to rapid environmental changes, but that is still not a reason to put a heat mat against a micro enclosure. Keep their containers in the stable part of the room and pay equal attention to moisture because a very warm tiny tub can dry far faster than expected.
If a species genuinely requires warmer conditions than the rest of the collection, solve that at rack or room scale with thermostatically controlled ambient heating and proper monitoring, not a concentrated unregulated hot patch.
Use the species temperature range
For a species listed at 20–25°C, keep the enclosure within that range and avoid prolonged extremes.
What matters is avoiding prolonged conditions outside the sensible range, especially sustained cold for warmth-dependent tropical species or overheating in summer.
Check the enclosure after changing room heat
Warmer air changes how quickly substrate and water dishes dry. If you raise the temperature of a spider room in winter, re-check tiny sling containers and moisture-dependent species rather than assuming the only effect is temperature. Ventilation and evaporation interact.
When room heating changes seasonally, recheck enclosure drying rate and water availability.