Connected to a chimney or stack on the outside of a building, a metal flue is a sheet metal pipe that ventilates a stove or boiler. In order to install a metal pipe flue, a sheet metal worker must measure the distance from the stove to the chimney or stack, then cut the pipe to length. Cutting a metal flue pipe is not labour-intensive, but it does require precision and care because sheet metal bends and warps with only a small amount of pressure.
Measure the distance required of the flue--that between the stove or boiler and the chimney or stack--and mark the flue with a felt-tipped pen. Roll to rotate the pipe around and mark the distance several times around the circumference of the pipe. Lay a piece of paper on the pipe, butt one edge up against the marks and draw a line along the edge around the entire pipe. (A cloth tape measure also works as a flexible straight edge.)
Put the pipe wall--at end of the flue that constitutes the extra length--in between the blades of the tin snips. Cut the tin by squeezing the two handles of the snips together. Cut the pipe along the bilateral centre line of the pipe, toward the marked line indicating the circumference.
Stop three inches from the marked line. Begin curving the cut until the cut meets the marked line. Cut around the pipe along the circumference line. Cut all the way around the pipe until the extra length is detached from the required portion of the flue.