If your door feels heavy, it is likely that your springs have started to wear down and are no longer capable of bearing the weight that they once did. Now, don’t worry, just because a spring is starting to lose its strength doesn’t mean it will snap at any moment. However, simultaneously, a weak spring isn’t any safer to try and repair on your own.
Garage door manufacturers typically produce garage doors fitted with torsion springs that provide a minimum of 10,000 to 15,000 cycles and are guaranteed for three to seven years. One cycle is a single opening and closing sequence. Most manufacturers offer a 30,000 cycle spring. However, it is important to remember that if the weight of the garage door is increased by adding glass, additional insulation, or even several coats of paint, the life of the torsion spring may be greatly reduced. Additionally, springs at highly humid environments, such as coastal regions tend to have a significantly shorter cycle life, due to the corrosive cracking.
Depending on the design, you can know in advance how many turns are going to have to be unwound. Lifting a 7-foot door by winding a cable on a 4-inch diameter (about 1 foot circumference) drum requires about 7 turns, plus one extra turn to maintain cable tension at the top-of-travel. Maintaining tension at the top-of-travel is critical; without it the cable will jump off the drum, requiring a serious repair.
Loosening or tightening the set-screws is the moment of most risk, since the end-wrench is a potential missile if you slip, and your hand is close to the cone. When the wrench is removed and only the rods are in place, it would seem that the worst that could happen is that the rod is flung out and the captive spring and cone rattle around, assuming you are keeping yourself clear of the rod's radial disk of rotation, and not leaning on the rod such as to fall into the apparatus were the rod to slip out of your grasp. The torsion shaft design has the virtue of capturing the mass of the spring and cones reliably on the shaft, preventing these parts from launching themselves as projectiles, even in an accident.
Roberto was very courteous and explained the details of what he was doing. He also pointed out a repair I might consider having done (replacement of the bottom panel of my door) and asked the office to follow up with me on this. Someone did follow up with me and since replacement of the bottom panel is not an option and I would have to replace the door, I decided that I can wait.
First, we always provide a written estimate that is signed before doing any work, fully explaining what we'll do in plain English so you'll understand it. When we've completed the job, we walk you through and show you what's been done so you can be confident that your door was fixed right. We stand behind the job with the industry's best warranty and our 24 hour call back policy.
Here are the new replacement springs I ordered from a distributor, which I found using a Google search for "garage door supply" (search that phrase now). You certainly won't find these at Home Depot or Lowe's (although last I checked Lowe's does carry the less daunting extension spring replacements). I also have a list of some suppliers at the end of this page.
Started in 2004, Aladdin Garage Doors has become known nationwide as the trusted source for garage doors, repairs, and fast, efficient service. With a mission focused on delivering outstanding customer care, we’re proud to offer garage doors that lead the industry in quality, value, and lifetime protection for homes and businesses. Whatever your garage door needs may be, you can count on Aladdin Garage Doors to offer:
As in an elevator, the electric motor does not provide most of the power to move a heavy garage door. Instead, most of door's weight is offset by the counterbalance springs attached to the door. (Even manually operated garage doors have counterbalances; otherwise they would be too heavy for a person to open or close them.) In a typical design, torsion springs apply torque to a shaft, and that shaft applies a force to the garage door via steel counterbalance cables. The electric opener provides only a small amount of force to control how far the door opens and closes. In most cases, the garage door opener also holds the door closed in place of a lock.
In the United States, the Consumer Product Safety Improvement Act of 1990 required that automatic residential garage door operators manufactured on or after 1 January 1991 conform to the entrapment protection requirements of the 1988 version of ANSI/UL standard 325. A requirement for redundant entrapment-prevention devices was added in 1993; such a system can use an electric eye, a door edge sensor, or any other device that provides equivalent protection by reversing the travel of the closing door if an object is detected in its path. 
If this manipulative, we-are-your-nanny business approach is truly in our best interests as consumers, then we shouldn't be allowed near ladders, lawn mowers, or power tools. Those products are just as hazardous and prone to misuse as torsion springs, yet no one thinks of them as forbidden. The only genuine difference is that torsion springs are a hazardous thing you need only rarely, while a lawn mower is a hazardous thing you need all the time.