The tightening of regulations related to particle emissions has made retrofitting the ESP into a hybrid of the ESP and a baghouse filter a possible solution to some old plants in Finland. The objective of this thesis was to assess when this is a viable option and to study the advantage and limitations of the system by comparing it to other options available to companies when they need to have more efficient filters. For this purpose, is was necessary to compile the pricing of a new ESP and bag house filter and compare it to the price of retrofitting an ESP in Finland and estimate its maintenance and operation cost. To achieve this, the following procedure was necessary: • study how a hybrid ESP is built and how it operates • compare a hybrid ESP to a conventional ESP and bag house filter to determine its limitations • compile an overview of the technologies behind an electrostatic precipitator, a bag house filter and a hybrid ESP-Bag house filter to illustrate their limitations and to determine when these technologies could be applied. • find out suppliers, their prices and options for the various parts of the Hybrid ESP-bag house filter, and the solutions they provide for some parts, such as valves, filter bags, the bag cage and the control system, if biofuel is used. The option for the filter was found and it was possible to give a general idea of how many of the options would affect the filter. An example process was used to better illustrate how the options affect the filter. It was also possible to derive the cost of operation and construction of the filter and compare it to that of a new ESP and bag house filter and give an overview of its advantages and disadvantages. In conclusion, there are processes where satisfactory results cannot be achieved by an ESP; thus, a fabric filter par become necessary and its operation cost are not always greater than those of an ESP.