Sunlight through glass is the biggest troublemaker
A vivarium works like a small greenhouse, and a patch of direct sun through a window can push its internal temperature far beyond the thermostat's control within the hour — the thermostat can switch a lamp off, but it cannot cool the box. The sun patch also moves across the room through the day and shifts with the seasons, so a spot that seems safely shaded in the morning can be in full sun by mid-afternoon, and a corner that is safe in winter may catch the lower sun of summer. Place the enclosure where direct sun never reaches the glass at any hour, and check the candidate spot at several times of day before the animal moves in.
Interior walls, radiators, and doors
An interior wall is the steadiest surface in most homes because the rooms on both sides cushion it. Exterior walls run cold in winter and warm in summer, radiators create a saw-tooth of heat each time the household heating fires up and cools down, and the floor area near an exterior door gets a blast of outside air with every arrival. Keep the vivarium away from all three influences. The same goes for kitchens, with their cooking heat spikes, and for spots directly under heating vents or in the path of air-conditioning, which can strip heat and humidity from the enclosure all day long without anyone noticing.
Height, airflow, and vibration
Warm air rises, so a vivarium on tall shelving lives in a warmer layer of the room than one near the floor — while floor level near a door is the draughtiest layer of all. A stand at a comfortable working height usually sits in the steadiest air and makes daily care easier on your back. Leave a small air gap behind and beneath the enclosure rather than wedging it into a sealed alcove, so heat from lamps and fittings can escape instead of building up around the box. Avoid busy walkways and the backs of doors: constant knocks, slamming, and foot traffic vibrate the glass and unsettle a shy animal even on days when the temperatures behave perfectly.
Prove the spot before the animal moves in
Run the empty, fully equipped enclosure in its new spot for at least two full days with a minimum-maximum thermometer inside. Read the extremes morning and evening: you are looking for a basking spot that reaches its target, a cool end that stays genuinely cool, and night temperatures that fall gently rather than crashing. If the cool end climbs too high on a warm afternoon, or the whole box sags cold overnight, the spot — not the equipment — is the problem, and it is far easier to learn that with an empty box than with a stressed animal inside it.
Seasonal checks once it is settled
A spot that behaves in spring may not behave in high summer or mid-winter, when the room's own temperature range widens and the heating runs to a different pattern. Recheck the minimum and maximum readings when the seasons turn, and whenever the room's use changes — a new radiator habit, curtains replaced, furniture rearranged. Small corrections, like shifting the stand a short distance from the wall for summer, keep the gradient honest without touching the equipment inside the box, and they cost nothing but attention.
Pin the placement notes and the test readings to your reptile's KinsLe Family Sharing page, and the next person tempted to move the enclosure toward the window can see the temperature log that argues otherwise.