Daniel
Do you just want to clean the extractor fan hood? or the ventilation ductwork as well?
If its the latter it is best to leave it to specialist kitchen ventilation cleaning companies, otherwise it means hiring heavy duty industial equipment like steam cleaners, 360o nozzels sprinklers, wet pick up vacs and collection canopies etc etc, and that without sometimes having to dismantle 3 phase fan motors that get in the way.
Basically the chemicals they use are `catersan` and steam, and sometimes `Carbon off`(do not use on aluminium).
You can buy them from
www.dynamic-chemicals.co.ukRegards
Keith