A slit fin heat exchanger is formed by wrapping slit fin tubing around a pair of mandrels having expanded metal cylinders thereon into a flat coil having two spaced rows of tubing. The flat coil containing the expanded metal cylinders is located on mandrels which are rotatable about spaced parallel axes with the mandrels and axes initially being in the same plane. The mandrels are rotated about their axes in opposite directions which shifts the plane in which the coil is located. The shifting of the plane of the coil moves a portion of a first row of the coil into contact with a planar portion of a platen and the second row of the coil into a nesting relationship with the portion of the first row which is in contact with the planar portion of the platen. Continued rotation of the mandrels causes folding of the portions of the coil which extends the area of nesting. The folding takes place through up to 120.degree. and the ends of the first row of the coil contacts a portion of the platen causing the formation of a knob at the end of each coil and the nesting of the coil to the ends of the coil and into the expanded metal cylinders. The expanded metal cylinders serve to support the coil throughout its functional life, as well as during the manufacturing process.