Question: Someone told me that a way to check to see if a surface was getting too hot was to take the ambient temperature plus a certain number of degrees. Does anyone know the number of degrees for this equation? Answer: I assume you are talking about combustible materials close to a fireplace or stove; such as a wooden mantle or trim, or a combustible wall. The allowable temperature is 117 degrees F plus ambient or room temperature. Some wood burning standards simply refer to 190 degrees F as the maximum which is roughly the same thing in most cases.