What is the difference between Thermal based and Water based chimney?
Water based Autocleaning:
These type of chimneys are having a small storage space (200-300 ml) inside the chimney which would be auto or manually filled up. there would be a sprinkling pipe around the filters. When you press the clean button on chimney, it will sprinkle hot water through on the filters and it will rinse the greese/ oil from the filter. The resulting rinsed oil would be collected in the collector cup/ tray which would be on the wall side below the filter.
While this method is which is mostly found in auto clean chimneys, you still need to clean your filters manully after a certain period. Without this auto clean method you may need to clean filters once in a week or fortnight based upon usage (by putting under running hot water tap).
Thermal based auto Cleaning chimneys:
have a heating coil instead of the sprinkling pipe like a heater element (not exactly). which get heated and melts all the oil on the filters. again the oil is collected in the cup/ tray.
while water based cleaning is more applicable in light usage, thermal based cleaning is generally used in heavy/ commercial usage. You may leave your specific questions in comments section or for complete chimney selection guide is here.