Of course, the best garage door openers offer much more than weather protection. They are quick and convenient when leaving or returning home. They can secure what might otherwise be a weak point of home security. Some can even alert you at work if your garage doors aren't closed properly. The challenge you face is finding the right one – this isn’t a product you can simply try out and return until you find the best fit for your situation.
All measurements should be in feet and inches. Step 1, measure across the existing door or desired space for the width, then up and down for the height. The rough opening of your space should be the same size as the door. Step 2, measure the sideroom, which is the space beside your door. Measure the width of the left side, and then the width of the right side. Step 3, measure the space above the door, which is called the headroom. Measure the height of the distance between the top of the door opening and the ceiling. Step 4, measure the ceiling, which is called the backroom. You’ll need to measure the distance of the garage door opening toward the back wall of your garage. You should have 6 total measurements in all once you’ve finished measuring the space. Keep in mind that having an automatic garage door opener installed might call for additional backroom or ceiling space.
Correct spring size is determined by factors such as the weight and height of the door. You cannot substitute a different spring and just tighten or loosen the winding to make it balance the load. Why? To maintain cable tension under all operating conditions, the spring must retain about one turn of unspent wind-up at the top-of-travel position, which with the lift drum size and door height predetermines the number of turns of winding at the bottom-of-travel; and furthermore the torsion of the fully-wound spring at the bottom-of-travel must be slightly less than that needed to lift the weight of the door when translated by the lift drums.
Spring rate and torque: In my spring replacement above, the wire size was d = 0.2253 inches, and the ID was 2 inches, giving a mean diameter D = 2.2253 inches. The number of coils is L/d = 24 inches / 0.2253 = 107, less about 5 dead coils on the winding cones, or 102 active coils. Thus the spring rate is K = (π*28.5*10^6 * (0.2253)^4) / (32 * 102 * 2.2253) = 31.8 in-lb/turn (IPPT). Winding 7.5 turns * 31.8 in-lb/turn yields a torque of 238 in-lbs per spring.