A chimney temperature of 250 degrees Fahrenheit above steam temperature indicates:

A chimney temperature that is 250 degrees Fahrenheit above steam temperature is an indication of poor efficiency in a steam system. When the temperature difference between the flue gases exiting the chimney and the steam temperature is significantly high, it suggests that a substantial amount of heat is being lost to the environment rather than being utilized to perform work in the steam process.

In an efficiently operating steam system, the flue gas temperature should be closer to the steam temperature, which means that less heat is escaping through the chimney. A smaller temperature difference would indicate that more of the generated heat is being effectively used, leading to higher efficiency. Therefore, when the chimney temperature is excessively high in relation to the steam temperature, it points to the system not capturing and using the maximum possible energy from the fuel, thus confirming poor efficiency.