Some facilities may not be able to prevent dusty gases from impacting the cold interior walls of a filter, which may become contaminated as a result. Ideally, in a start-up, clean gases heat up the filter, so that when gas with material arrives, the temperature is out of the danger zone.

However, sometimes this is not possible, so an additional gas circuit can be installed, consisting of a pipe between the contaminated and clean air to handle a proportion of the gas, for example, 20-25% of the nominal flow, with a circuit and a heating system. This heating circuit is turned on before start-up or during breaks in the process and is controlled by thermostats. It performs a function similar to the heating of the filter walls, and is used in difficult cases.