I Need A Domestic Kitchen Hood Over A 5 Burner Gas Hob To Extract And Duct 5 Metres.

Mike Newman would like to know the answer to the following question, if you have a suggestion then please post a reply:
The oven and hob are on an inside wall and I need to duct round one corner a total of 5 metres to an outside wall. What power of chimney hood extractor do I need?