'Allo 'Allo! S05E03 - Dinner with the General

Rene's photograph of the safe in Gruber's bedroom (containing the plans for the German invasion of England) is identified by Leclerc as a Kaisenhoff Rosenbaum Swartzburger 16-Lever Multi-Counter Mark Three. Leclerc and Rene are to blow the safe; Edith is to create a diversion by dropping a smoke cannister down Gruber's chimney. Now, was it the third or the fourth chimney counting from the west?