Definition
A torsion spring is a long, tightly wound steel coil mounted on a horizontal shaft directly above the garage door opening. It works by torque, as the door closes, the spring is wound tighter and stores rotational energy; as the door opens, it unwinds and lifts the door weight off the opener motor.
Residential torsion springs are spec'd by three numbers: wire diameter (e.g. .250"), inside diameter (typically 1¾" or 2"), and length. The combination of those three values plus the door's weight determines the spring's lift capacity and its cycle rating.
Most homes have one torsion spring on a single-car door and two on a double-car door, when one of a matched pair breaks, the other usually has roughly the same remaining life and gets replaced at the same time.
Why it matters to Nashville-area homeowners
Nearly every garage door we service in Brentwood, Franklin, Nashville, and across Middle Tennessee is balanced by a torsion spring. When one breaks, and they do, on a normal cycle-fatigue schedule, the door becomes too heavy for the opener to lift safely and the system has to come down. Torsion springs are under enough tension to cause serious injury and should always be replaced by a trained technician. Don't attempt a DIY swap from a hardware-store kit.
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Source
DASMA Technical Data Sheets (Door & Access Systems Manufacturers Association) →
How this definition is reviewed
Definitions reviewed against UL 325 (Underwriters Laboratories Standard for Door, Drapery, Gate, Louver, and Window Operators), CPSC 16 CFR Part 1211 (federal residential garage-door-operator safety rule), DASMA technical data sheets, and current manufacturer specs from LiftMaster, Chamberlain, Genie, Clopay, and Amarr. Locality notes draw on in-the-field experience in Middle and East Tennessee homes built between the 1960s and the present.
