Constant Force Window Balances Explained

All modern single hung and double hung windows have a built-in balance system that makes it easy to open and close the window sash. When you’re ready to shop for new or replacement windows, understanding the value of each balance system will help you make a confident decision. In this post, we’ll explain everything there is to know about constant force balances by answering some frequently asked questions.

What is a Constant Force Window Balance?

A constant force window balance is the mechanism that allows windows to open and close smoothly. The balance allows the window to remain open without the use of a prop to hold it up.

This balance system uses a stainless steel coil similar to a tape measure to raise and lower the sash. The tension in the coil remains constant and easily extends and contracts to operate the window. Larger windows are heavier and put more strain on the balance system. To provide the right amount of counterbalance more coils are added to the balance system.

Constant force balance manufacturers use computer programs to measure the dimensions of the window and calculate exactly how many coils to use in the window. This system ensures that each window has the proper counterbalance for longterm use.

^{Image Credit: All About Doors}

How does the constant force balance work?

The main parts of this balance system are the coil, the balance spring cover, the balance drum, and the pivot lock shoe.

The coil is set over the balance drum and the balance spring cover over both. The coil is attached to the shoe and the sash latches into the shoe. In the jamb of the window is a place for the balance coil to be screwed into, this holds the coil in position when operating the sash. The sash is caught on the shoe which is attached to the coil when the sash is lifted and lowered the coil balance contracts and extends. It’s as easy as imagining the extension and retraction of a tape measure.

^{Image Credit: Gfycat↗}

How Do I Know Something Is Wrong With My Window Balance?

Constant force window balances are the most reliable type of window balance. Unlike other balances, this system uses a stainless steel coil that won’t rust or lose tension. Serious problems with this balance are unlikely but if you do run into an issue, it’s fairly easy to replace the balance (more on that later in this post).

The most common problem we run into with constant force window balances

Many of our most popular windows feature constant force window balances. We have yet to run into a serious problem with this type of balance but we do sometimes receive calls from our customers saying their new replacement windows won’t close or won’t stay open. Some might think, “wow, it already broke,” but this is rarely the case.

The particular problem our customers run into is on windows with a tilt sash. The issue is that the sash isn’t sitting in the shoe correctly. The sash can become disengaged from the shoe two ways:

When the homeowner tilts the sash from too low a position. Tilting the sash from the bottom of the window frame can cause the sash to pop out from the shoe, it can be one or both shoes. If the homeowner doesn’t notice and the sash isn’t completely removed they push the sash back into the jamb and when they go to close the window it won’t lower all the way.
When the homeowner removes the sash from the jamb and puts it back in without placing the sash into the shoes. In this case, if the sash is in the jamb below the shoes it will just fall instead of staying open. If the sash is put in the jamb above the shoes, it will rest above the shoes but won’t close all the way.

The window sash has a small rod at the bottom of the left and right corners. These rods should sit completely in the shoe, once in place, they’ll latch on and operate as intended.

If the sash is properly engaged in the shoes of the balance and the window is still difficult to lift or lower, then there is a problem with the balance.

Pros and Cons of Constant Force Window Balances

Benefits of constant force window balances

Features stainless steel coil springs that won’t lose tension
Stainless steel coated springs resist corrosion
A low-friction coil system requires less force to operate
Smoother and quieter operation than other balance systems
Can be designed for larger heavier window units
Low failure rate
Doesn’t require tensioning adjustments

Drawbacks of constant force window balances

The sash stop at the top of the frame prevents the sash from opening all the way

How To Replace a Constant Force Window Balance

When a constant force window balance fails it needs to be replaced. If you can identify and source the original parts of your window, balance replacement should be easy. Follow the steps below to replace your constant force window balance.

Step 1: Remove the sash

Unlock the sash
Lift the sash at least 4 inches and engage the tilt sashes
Tilt the sash in and grab the window from the back (close to the frame)
Lift the sash out from one side and then the other (it needs to pop out, this can be difficult on some windows)

Step 2: Unlock the pivot shoe

Use a screwdriver to turn the pivot shoe into an unlocked position
Once unlocked raise the shoe up to the balance assembly

Step 3: Remove the jamb liner and sash stop

If your window unit has a jamb liner, use a screwdriver to pop the liner out of the jamb
Use a screwdriver to pop the sash stop out from the top corner of the jamb
There will be a notch at the top of the jamb

If you are replacing both balance systems repeat steps 2-3 for both sides of the jamb.

Step 4: Remove the balance system

Use the screwdriver to detach the balance system from the jamb
Run the balance up to the notch and out of the jamb

Step 5: Replace the balance

Take your replacement balance and slip it into the jamb through the notch at the top of the jamb
Slide the balance down to where the old balance was
Screw the balance into position
Lower the pivot shoe so that it is at about the same position across from the opposite shoe
Make sure the open side of the shoe is facing up so that the rod on the sash can latch on

Step 6: Replace the sash stop and liner

Pop the sash stop into place at the top of the jamb
Pop the sash liner into place in the side of the jamb

Step 7: Replace the sash

Take the sash and place it back in the jamb and shoe, one corner at a time
Once the bottom two corners are in the shoe tilt the sash up and push it back into the frame
The sash should now operate as designed

If you’ve followed all of these steps but now the window won’t close all the way, the sash is probably not latched in the shoe. Tilt the sash down and make sure the sash is fully engaged in the shoe.

Which Window Brands Have a Constant Force Window Balance?

Most window vendors are manufacturing windows with constant force or block and tackle balance systems. The list below identifies the windows we sell which feature constant force sash balances.

Brennan Signature Single Hung Windows
Brennan Traditions Double Hung Windows
Brennan Traditions Single Hung Windows
Brennan Solar Bear Single Hung Vinyl Windows
NT Presidential Series Windows - Single and Double Hung
Milgard Tuscany Double Hung Vinyl Windows

Homeowners interested in new or replacement windows should visit a showroom to operate different styles of windows and different styles of window balances. While our favorite is the constant force balance, it’s not the only option.

For an overview of all window balances, check out our Window Balances 101 blog post.