Accurate Thermostat, Yet Uneven Heating?

Take a gas griddle as an example. From the temperature setting to the moment heat actually reaches the food, the process generally follows this path:

The thermostat senses the temperature at a specific location and adjusts the heating condition through the gas control system. However, once heat leaves the burner, it must still pass through the griddle or cookware before it finally reaches the food.

Therefore, “the control point being close to the set temperature” and “the entire cooking surface maintaining the same temperature” are actually two different things.

The ASTM F1275 test method for commercial griddle performance also evaluates thermostat accuracy separately from temperature uniformity across the cooking surface. In other words:

Control Accuracy ^{Note 3} ≠ Temperature Uniformity ^{Note 4}

After heat enters the metal from the burner, several common factors can affect how it is distributed.

The first is Thermal Conductivity ^{Note 5}. Different materials transfer heat outward at different rates, so when one area receives stronger heating, the speed at which heat spreads to surrounding areas can also differ.

Another factor is thickness. A thicker pan base or griddle plate generally provides more material through which heat can spread laterally, but it may also change preheating time and temperature response.

Another important factor is Thermal Mass ^{Note 6}. When a large quantity of refrigerated food is placed on a griddle at once, the surface temperature drops. A cooking surface with greater thermal mass is generally less likely to experience a rapid temperature drop over a short period.

In addition, the flatness of the pan base or griddle, actual contact area, flame coverage, burner arrangement, and the location of the temperature-sensing element can all affect the final temperature distribution.

Previous heat-transfer studies on multilayer metal cookware bases have also shown that material and construction can affect surface temperature distribution after heating. Therefore, cooking performance should not be judged simply by whether cookware is expensive or inexpensive. A more useful question is whether the cookware matches the equipment's heat source, construction, and actual cooking method.

Uneven heating does not always mean a faulty thermostat

If a griddle shows a pattern such as “the left side burns easily while the right side cooks more slowly,” it is natural to suspect the thermostat first.

For a more complete diagnosis, however, it is useful to check not only whether the thermostat's sensing point is accurate, but also the actual temperatures at different areas of the griddle, gas pressure, flame condition, burner arrangement, the condition of the griddle or cookware, and the actual cooking load.

ENERGY STAR materials on commercial griddles also note that improving cooking-surface temperature uniformity can involve not only better thermostat control, but also factors such as high-thermal-conductivity griddle materials and temperature-sensor placement.

In other words, an accurate thermostat is important, but it controls only one part of the overall system.

For commercial kitchen equipment designers, the ideal result is not simply that “one component is highly accurate,” but that temperature sensing, gas control, combustion, heat transfer, and actual cooking load work together effectively.

Alpha Brass Controls has long developed thermostats, gas valves, and related combustion-control components, all of which play important roles in the temperature-control chain. From the perspective of the complete appliance, however, component-level control performance still needs to work together with the proper burner, griddle plate, cookware, and temperature-sensing arrangement before it can translate into stable cooking performance.

So the next time the set temperature appears normal but food still heats unevenly, it may not be necessary to immediately assume that a specific component has failed.

Sometimes, what deserves a closer look is the entire heat-transfer and control chain.