Abstract: In a process for thermal pest control, a fuel-operated heater with separate flue gas routing is used to heat up a space to be treated. Fumigants may be additionally introduced into the air of the space to be treated, especially if the combustion chamber 13 of the heater is separated from the heat exchanger chamber 8 of the heater in a gas-tight manner. The process is particularly suitable for disinfecting mills and food-processing plants.