Constant Force vs. Block and Tackle Window Balances: What’s the Difference?

Introduction
When it comes to window performance, the balance system plays a key role in how easily and reliably your windows open, close, and stay in place. Two of the most common types of window balances used in modern double- and single-hung windows are constant force and block and tackle balances. But what sets them apart—and which is right for your window?

Let’s break down the differences, features, and benefits of each system.

What Is a Window Balance?

A window balance is a mechanical device hidden in the window frame that helps support the sash during operation. It counterbalances the weight of the window, allowing for smooth and controlled opening and closing without excessive force.

What Are the Primary Types of Balances?
1. Constant Force Window Balances
a. How They Work

Constant force balances use a coiled stainless-steel spring mechanism mounted in a cassette. The coil provides a consistent tension to counteract the weight of the sash throughout its entire range of motion.

b. Key Features
· Made from stainless steel
· Compact and corrosion-resistant
· Often used in modern vinyl or aluminum windows
· Typically designed for lighter window sashes

c. Benefits
· Smooth operation with minimal friction
· Durable and low-maintenance, thanks to fewer moving parts
· Consistent tension for reliable performance over time
· Slim profile ideal for narrow frame designs

d. What Are These Best For?

Constant force balances are best for light to medium-weight windows, where space and longevity are key. This a key go-to option for residential vinyl windows.


2. Block and Tackle Window Balances
a. How They Work

Block and tackle systems use a combination of pulleys (blocks), a cord or sash rope, and a spring. When the window is opened or closed, the spring stretches or compresses, while the pulleys reduce the effort needed to move the sash.

b. Key Features
· Uses multiple components: spring, pulley, and cord
· Can support heavier sash weights
· Common in wood, vinyl, and older aluminum windows

c. Benefits
· Strong lifting power, ideal for heavier or larger windows
· Versatile—can be adapted to a wide range of window sizes and materials
· Proven design with a long track record of use

d. What Are These Best For?

Heavier or larger windows, including historical or custom wood-frame windows. Having said this, various modern manufacturers have chosen to use block and tackle balances because of their strength and durability over thousands of cycles of use.

So, which option should you look for when selecting windows?

​Feature 
Durability:
Ease of Operation:
Maintenance:
Best For: 

Constant Force
​High (fewer moving parts)
​Smooth and consistent 
​Low
​Modern, lighter windows

Block and Tackle
​Moderate-High (more wear points)
​Stronger lifting power
​May require occasional service
​Heavier or traditional windows

Final Thoughts
Both constant force and block and tackle window balances are very reliable systems—but each has its own unique characteristics.

If you’re looking for a sleek, long-lasting balance for lighter, modern windows, constant force is a smart choice. If you need extra lifting power and flexibility for heavier or oversized sashes, block and tackle delivers.

Need help weighing the pros and cons of these balance options as you shop for windows? Contact our team—we’re happy to help you choose the perfect solution for your home or project.