There are many types of temperature test chambers, but they all have limits of high and low temperature. Let's take a look at the typical high temperatures thresholds and why they exist.
Test chambers usually have wire heaters made of a material called Nichrome. By placing successive loops of heater wire, a greater amount of heat that is generated. The result looks a lot like the inside of a toaster. Fans circulate the air past the heaters, so the samples in the chamber are not exposed to radiant heat. It is very easy to add heaters and increase the speed and/or high limit of a chamber.
ESPEC chambers typically have a high temperature limits under 200°C. Here is a break-down of why a chamber's high temperature limit exists:
Limit to 85°C: Our panelized walk-in chambers cannot go higher than 85. These units use expanded urethane for insulation. Urethane can start to degrade at temperatures above 85°C. For walk-in customers who need higher temperatures, we switch to a fiberglass insulation. The benchtop customer can switch to another model. Since fiberglass insulation isn't rigid, we have to include an angle-iron frame, so we call these models one-piece or solid-construction.
150°C: There are two reasons we may limit a chamber to 150°C. First, there may be a limitation of the materials used inside the chamber. Secondly, for extremely fast chambers, we may limit the high temperature to avoid problems with accidentally tripping overheat protection devices.
170-180°C: Most models stop at this temperature range. There is a risk of burning the oil inside the refrigeration's cooling coil.
210°C: Because thermal shock chambers separate the hot and cold sides, we don't have to worry about the refrigeration oil. However, temperatures around 200°C are approaching the limit of several materials used in constructing the chamber.
300°C: Significant changes to the construction and materials of the chamber can allow an even higher temperature. In this case, the refrigeration coil is isolated from the chamber by dampers, so that it is only exposed when required. This would be strictly a custom-built chamber.