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How to Use Brush Seals for Sash Windows

Graeme Clarke August 28, 2018 Draught Seals

Sash window brushes, when used correctly, can serve as an effective draught seal for your windows. With double hung windows or any other windows with sliding sashes, brush seals can work beautifully when you want to stop as much wind passing through your windows as possible. Brush excluders can fit in those really tight spaces where other types of draught seals may not work as well.


Getting your draught seals to work optimally is key to dealing with your draught problems and reducing your household heating costs. Leakage from the gaps around your doors and windows can drive your heating costs up by as much as 25%. With brush draught excluders for sash windows, as well as silicone rubber seals, which are an ultra-practical solution for draughty windows, you can enjoy a permanent solution for draughts. This means lower energy bills and greater energy efficiency but, even more importantly, a more comfortable home.



Why Brush Draught Excluders Are Used for Windows

A lot of people think of brush seals as a draught excluder for doors. They are often installed on the bottom of the door as a DIY fix for slowing down cold air currents. Most people don’t think of using brush seals for windows but they actually can be the ideal choice for certain situations. They aren’t helpful for every type of window, but they do play an important role for draught proofing sash windows.

At Thermawood, when we retrofit double glaze timber windows, we include draught seals in the process as standard. Using a rubber seal – which offers both draught and acoustic benefits – we can dramatically reduce draughts while also boosting the acoustic performance of your windows.

Even better, we machine the seals directly into the frame or sash with our special tooling so they become a permanent part of the window. As a result, the windows still retain their original charm – you won’t notice the draught seals – and you have a permanent answer to draughts. Even with century-old draughty wooden windows that you thought were hopeless, you can still reduce draughts dramatically with the right seals in the right places.


With sash window seals, brush excluders can help when you have zero compression. Because brush seals can be crushed down to almost nothing, you’ll achieve excellent results in the tight spaces that silicone seals may not fit into as seamlessly. The brush hairs will slow down the wind but you’ll still be able to easily slide the sashes.



Where to Use Sash Window Brushes Correctly

While we use rubber seals for casement windows, when you have sliding movement, we may also use sash window brushes. Ultimately, however, there’s really no one-size-fits-all solution for any window. So what we do is, we evaluate the unique needs of the window to determine how best to address any gaps that are causing the draughts.

This is especially true with older timber windows, where there may be uneven surfaces or you have to be really careful with the type of draught excluder you use so the window will still function properly. With most windows, we can machine in the silicone seals, effectively draught proofing while creating a seamless look. It’s with some sash windows that brush seals come into the picture.

When we use brush seals, we use a special mohair brush seal with a fin seal. The mohair does an excellent job of inhibiting draughts. These are the two main areas where you can correctly use window brush seals and see great results:

  • In the middle rail of double hung windows, brush seals will act as a wedge. They wedge aaatogether, creating an incredibly tight seal that is compressed down to almost nothing.
  • Down the sides of double hung windows, you’ll also get a really tight fit between the sash and aaathe frame.



The Advantage of Sash Window Brushes

Using brush seals makes it possible to completely draught proof a window using permanent draught excluders. Unlike putting up foam strips or other draught proofing kits you may find at the hardware store, you don’t have to worry about your draught proofing falling off when you open the windows or sticking to the frame.

The goal of draught proofing is to stop cold air from entering and to actually enjoy a noticeable difference in both your energy bills and in the comfort of your home. But, you don’t want to have to keep installing your draught excluders every season, which is the case with a lot of DIY options.

Nor, do you want to sacrifice the operation of your window – with foam seals that are stuck on the frame or sashes with self-adhesive tape, you may not be able to just open your windows when you want to let in the fresh air. And, you want the draught seals to actually work, which means you need that perfect balance between a smooth, tight fit that doesn't neglect any gaps yet still lets you open your windows without a problem.

Sash window brushes, placed where you can get that really tight fit, like you can down the side of double hung windows and in the middle rail, make it possible to retain the fluid movement of your windows all year round. And, a powerful draught seal.

Combine this perfect solution for draught proofing windows with Thermawood’s patented dry Retrofit Double Glazing system, and you have an efficient, cost-effective, timeless solution to both draughts and all-season insulation. And, your windows will still look amazing.

To learn more about what is possible with draught proofing today, download, “The Ultimate Guide to Draught Sealing Windows and Doors.”


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