Sash Balance Versus Spring Versus Cord Decision Tree

Why this matters

A double-hung sash that falls when released, or rides up when opened, is one of the most common service tickets in a window business. The fix is fundamentally different across three eras of construction. Pre-1955 wood units use weight-and-cord systems, mid-1955 through current production uses spiral or block-and-tackle balances, and a small slice of premium product uses constant-force tape balances. Calling a cord problem "a spring" or a spring problem "a cord" sends the wrong part to the truck. Worse, on weighted units the lay person and even some installers assume balance failure means a balance device when the sash is actually too heavy for its original sash weights because someone reglazed it with thicker glass. The branch points below resolve which system you have and which subsystem failed.

Symptom presentation

The complaint comes in three flavors. Sash falls when released - common across all three balance systems and usually means a balance has failed or disconnected. Sash rides up when opened - exclusive to spiral and constant-force tapes, indicates a balance with excess preload, often after someone "fixed" it by overwinding. Sash stays put but feels stiff or scrapes - this is a friction problem on the jamb liner or sash track and is not a balance issue, do not order parts before testing.

Note the year of the unit. Pre-1955 construction with parting-bead jamb stops, no visible jamb liner, and a wood casing wider than 4 inches is almost certainly a weighted system. A jamb liner extruded vinyl or aluminum with a visible spiral or coil channel is a modern balance system. A constant-force tape (Caldwell, Amesbury Truth) shows as a flat metal coil mounted in the jamb pocket, easily mistaken for a tape measure.

Quick checks before opening anything

Operate the sash through its full travel and listen. A grinding or rasping sound on a spiral balance indicates a stripped pivot foot or a rounded spiral rod. A clicking sound on a block-and-tackle balance indicates the cord has jumped off the pulley inside the cartridge. A heavy thud at full lift on a weighted system suggests one of the sash weights has fallen off its cord and is sitting at the bottom of the weight pocket.

Pull the sash to half-mast and release. Time the fall. A sash that drops from half to full close in under 2 seconds has a failed balance. A sash that holds for 30 seconds and then creeps is borderline; check for friction first. A sash that rides up immediately on release is overcompensated.

Check both sides. Often one balance has failed and the other is doing all the work, which both feels uneven and accelerates failure of the surviving balance. Confirm symmetric behavior at three travel positions: full lift, half, and quarter-open.

Isolation tree

Branch 1 - weighted system (pre-1955 or restoration unit). Remove the parting bead and lift the sash out of the jamb. Inspect the sash cord at the side of the sash; the cord runs from a knot or wedge in the sash stile, up through a pulley at the head jamb, and down to a cast-iron sash weight inside the weight pocket. A broken cord drops the weight to the bottom of the pocket; you will see the cord end dangling at the pulley. Replace with new sash cord (nylon or cotton, sized to fit the pulley sheave, typically 7/32 inch). Reweigh the sash: the combined weight of both sash weights must equal the sash weight within 1 pound. If a homeowner has reglazed the sash with thicker insulated glass instead of single-pane, the original weights will be too light and the sash will fall even with new cord; add weight or convert to a modern balance kit.

Branch 2 - spiral balance (most vinyl and aluminum-clad double-hungs from the 1970s onward). Tilt the sash inward (modern tilt-in units), disengage the sash from the balance shoe at the bottom of the jamb liner. Inspect the spiral rod for visible twist damage, stripped threads, or a missing pivot tang. Pull the balance out and rotate the spiral by hand; it should turn smoothly with consistent spring tension. Order replacement balances matched by length and stamped load rating (the number on the side of the balance, expressed in pounds per balance, typical range 8 to 38 pounds). Two balances per sash must match.

Branch 3 - block-and-tackle (constant-force is similar but mechanically distinct) balance. Open the cover panel on the jamb liner if present, or pull the balance cartridge through the sash channel. The block-and-tackle uses an internal pulley and cord arrangement that fails when the cord frays at the pulley. The failure mode is distinctive: the sash falls suddenly with no warning rather than degrading over time. Replace the full cartridge; do not attempt cord-only repair in a sealed cartridge.

Branch 4 - constant-force tape. The coiled steel tape mounts in the jamb pocket and the sash attaches via a slot at the bottom edge. Failures are usually at the attachment point where the tape end has separated from the sash. Inspect the tape coil for kinks; a kinked tape will not retract smoothly and is junk. Replace per the manufacturer's tape kit.

Branch 5 - sash holds position but feels stiff. The balance is working. Inspect the jamb liner for paint overspray, debris, or a swollen weatherstrip pile. Clean the liner and re-lube with a silicone spray (never oil-based products, they collect dust and degrade vinyl liners). If the sash still drags, the sash itself may be racked, check diagonals.

Confirming diagnosis

Pull the sash out and weigh it on a bathroom scale or hanging scale. Compare to the load rating stamped on the balance. The sum of both balance ratings should fall within 10 percent of the sash weight; outside that range and the sash will either fall (balances too light) or ride up (balances too heavy). After replacement, reinstall the sash and time the fall again at half-mast; a properly balanced sash should hold within 1 inch of where it was released for at least 30 seconds.

For weighted systems, calculate the required weight as 1.0 to 1.05 times the sash weight, distributed evenly between the two weights. A sash that has been double-glazed in renovation must be reweighed; original weights almost never match the new mass.

Remediation

References

• AAMA/WDMA/CSA 101/I.S.2/A440 - operating force and balance retention requirements for hung windows.
• ASTM E2068 Standard Test Method for Determination of Operating Force of Sliding Windows and Doors - the bench test method for force compliance.
• IRC R609 - residential code reference for window operation and emergency egress.
• AAMA Service Bulletin 909 - field service procedures for sash balances.
• Caldwell and Amesbury Truth service catalogs - OEM balance sizing and load rating reference tables.