Lay the copper tubes next to each other with the ends even.
Holding both copper tubes together, insert the tubes side-by-side into the vise with approximately three inches on one side and the rest on the other side of the jaws. Gently tighten the vise, being careful not to crush the tubes.
Place the cylinder up against the tubes, then gently bend the tubes around the cylinder.
Bend the tubes into a tight coil until about three inches of copper tubing is left. The coiled tubes should touch each other all the way down the cylinder.
Slide the cylinder out of the center of the coil.
Wrap the insulation around the coil.
Remove the coil from the vise. Hot water is to flow in through one end of one tube while cold water flows through the other end of the other tube. This will cause the hot water to warm the cold water as they each flow through the heat exchanger.