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On original sash windows, the sash was nothing more than a sliding pane, pegged open to stop it falling.

Later, ropes and then chains were used to make lifting the sash easier, as the weight of the glass was counterbalanced by lead or cast-iron weights. This meant wooden windows were very easy to open, as they hung freely in the rebate (when not painted shut) and remained static when opened because the lead and glass were counterbalanced.

Today we use the same principle of counterbalancing the weight of the sash, but glass is at least three times heavier and there is insufficient room for three times more lead.

Sash window manufacturers make five basic types of balances to choose from. These vary in budget and effort required to raise or lower the sash:

Clock springs or constant force balances

Block and tackle or cord and pulley balances

Wind up balances (Alumatilt)

Pretensioned Spirals (Ultralift)

Pretensioned double sprung balances (Torso)

We don’t make spring balances; we have used Caldwell Hardware as our supplier since we started making sash windows 31 years ago. This is because they make each type of balance mentioned above, but refuse to import some to the UK because they consider them to be inadequate for the UK market.

Some UK companies ignore Caldwell’s advice and import balances direct from the States. This means you may get offered windows with balances that are unlikely to perform as you may expect. Should you need detailed information, visit

An Overview of Balances

Clock Springs

These are larger versions of clock springs, like a metal tape measure on its side, which unfolds when the window is operated. Used extensively in America for secondary glazing or ultra-lightweight double hung windows, when tested to the American Manufactures Association tests (AMA) they are not expected to exceed more than 3,000 opening cycles. They are extremely cheap but Caldwell, who manufacture them, refuse to import clock springs into the UK. They’re simply not sturdy or strong enough for the windows found on the UK market and give no assistance when opening a sash. Masterframe never use clock springs.

Block and Tackle

Again, extensively used in the US for small, lightweight windows. They consist of a nylon cord approximately 2mm in diameter, wrapped several times around a pulley system and housed within a three sided channel. These balances are also very cheap to import but not expected to exceed 3,000 cycles. Caldwell make them for the American market and don’t import them to the UK for the same reasons – they provide no assistance when opening a sash. Masterframe never use block and tackle balances. 

Wind-up Balances (Alumatilt)

These are a lightweight balance for small windows or infrequently used windows. A continuous tube encases a twisted metal rod, known as a spiral. Although reasonably sturdy and competitively priced, they need to be “wound up” to the desired tension.

They remain twisted throughout the expected 5,000 opening cycles, however they are known to relax, meaning the upper sash will drop of its own accord, requiring adjustment.

This twisted state means that for its entire life, the balance looks to unwind if mishandled. A two-year warranty is average for this product that is highly likely to require some adjustment at some point in its life, however they do offer some assistance towards lifting sashes. Masterframe only ever offer wind ups if specified by clients.

Pre-Tensioned Spirals (Ultralift)

This is a smooth operating balance, with the tension set in the factory or pre-tensioned. A spiral rod held against a spring encased within a plastic tube makes Ultralift an excellent balance. They are designed for sash weights up to 28/30kgs. They have been independently tested at the BBA to exceed 20,000 opening cycles (that’s over 25 years if opened twice a day). The Authentic sash window come standard with Ultralift balances.

Double Sprung (Torso (II)

Vintage and Heritage sash windows come standard with high-performance Torso II balances tested to 50 000 cycles.

Designed by a Dutchman in 1946, they epitomise great engineering. Individually manufactured in 0.5kg increments (1lb) and tailored for perfect lengths, these balances have two springs; one wound clockwise, the other wound anti-clockwise

As a sash is opened, one spring extends, getting longer, and the other compresses, getting shorter, so they are counterbalanced for their entire life. This means they are immensely reliable and in general offer 30% extra assistance when lifting the sash.

The Torso II may be expensive but it remains the ultimate spring balance and can be made to suit any length or weight of sash.