We match the spring to your door's weight and height rather than guessing off a chart, because a spring that's slightly wrong will either fight the opener or let the door drop too fast. We replace both springs on a double-torsion setup even if only one broke - the second one is on the same clock and rarely worth leaving in. We check the cables, the drums, and the bearing plates while we're up there, since a spring failure sometimes takes a cable partway with it. The job itself, once we're on site with the right spring, generally runs under an hour of actual wrench time; the variable is what we find once the door's opened up. If the shaft is bent or the drums are cracked, that's a different repair and we'll say so before starting rather than after the invoice.