Energy Efficiency of Sash Windows: A Comparative Analysis

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Experts in Sash Windows Repair & Restoration, Timber Windows & Timber Doors in east midlands

Why Trust Sash Window Refurbish?

Sash Windows Refurbish specializes in providing repair and restoration services for wooden windows and doors in the UK, as well as various types of carpentry. During the process of fulfilling orders, we utilize a range of tools and paints, including saws, sprays, primers, resins, and adhesives. With more than 20 years of experience in carpentry, we have tested and used various brands and types of work tools, making us well-equipped to offer helpful advice on selecting the right tools and paints for your needs. Read more ...

Do Sash Windows Save Energy?

Sash windows, by their design, can help save energy when properly installed and maintained. The key lies in their ability to create a tight seal when closed, minimizing drafts and preventing heat loss during colder months.

However, the energy-saving capacity of sash windows depends on various factors, including the quality of insulation, glazing, and installation. Homeowners must invest in well-insulated sashes and ensure proper fitting to maximize energy efficiency.

Can Sash Windows Improve Home Energy Efficiency?

Yes, sash windows can significantly enhance home energy efficiency when chosen wisely. Opting for double or triple glazing can improve insulation, reducing heat transfer between the interior and exterior of the house.

Properly maintained sash windows, with well-fitted frames and weatherstripping, can prevent air leakage, further enhancing energy efficiency. Regular maintenance, such as repainting and sealing, is crucial to ensure the windows retain their efficiency over time.

How Energy Efficient Are Wooden Sash Windows?

Wooden sash windows, when crafted from high-quality timber and properly insulated, can be remarkably energy efficient. Wood is a natural insulator, providing a certain level of thermal resistance.

Additionally, wooden frames can be thicker than their uPVC counterparts, allowing for deeper glazing pockets and improved insulation. However, wooden sash windows require regular maintenance to prevent rot and ensure their energy efficiency is maintained.

How Energy Efficient Are uPVC Sash Windows?

uPVC sash windows have gained popularity for their durability and low maintenance requirements. In terms of energy efficiency, uPVC windows can be highly effective. They offer good insulation properties and are resistant to moisture and rot. uPVC sashes often come with multiple chambers within the frame, enhancing their thermal performance.

Additionally, uPVC windows can accommodate double or triple glazing, further improving their energy efficiency.

Which Is More Efficient: uPVC or Wooden Sash Windows?

The choice between uPVC and wooden sash windows depends on various factors, including budget, aesthetics, and maintenance preferences. uPVC sash windows are generally more cost-effective and require less maintenance. They offer excellent energy efficiency, making them a practical choice for many homeowners.

On the other hand, wooden sash windows, while potentially more expensive and demanding in terms of maintenance, offer classic aesthetic and natural insulation properties. Both options can be energy efficient when chosen and installed correctly.

Window Sash vs Cladding: Making the Right Choice

When considering sash windows, homeowners often face the dilemma of window sash vs cladding. Cladding, typically made from materials like aluminum or uPVC, is an external layer attached to the window frame.

It provides additional protection against the elements, enhancing the window’s durability. While cladding can improve a window’s lifespan, it’s essential to balance this with aesthetic appeal. Some homeowners prefer the traditional look of exposed wooden sashes and might choose regular maintenance over cladding.


How much heat is lost through sash windows?

The amount of heat lost through sash windows can vary based on factors like insulation, size, and quality. Generally, older sash windows without proper insulation can be less energy efficient, leading to significant heat loss.

What type of windows will be the most energy efficient?

Energy-efficient windows typically have double or triple glazing, low-emissivity coatings, and gas fills like argon between the panes. These features help to trap heat inside and prevent heat loss, making them the most energy-efficient choice.

How do you insulate sash windows for winter?

Sash windows can be insulated for winter by using weatherstripping, adding thermal curtains, or applying window films. Additionally, using draft stoppers around the edges and using window insulation kits can also help trap heat inside and prevent drafts or use our service.

What type of windows prevent heat loss?

Windows with double or triple glazing, low-E coatings, and insulated frames are designed to prevent heat loss effectively. These windows create a thermal barrier, reducing the transfer of heat between the interior and exterior of a building.

What is the sash windows U value?

The U-value of a window represents its thermal transmittance, indicating how effective it is as an insulator. The U-value for sash windows can vary based on their construction and materials, but lower U-values indicate better insulation, meaning less heat loss.

About the author

Glen Ramsey, who presently holds the positions of customer support and content manager, is a cherished member of the Sash Window Refurbish team. He is in a unique position to provide advice on all questions pertaining to the renovation of historic windows because he has a wealth of experience in all elements of window renovation, dealing with clients regularly and assisting them in choosing the best window-related course of action. He oversees the creation of information for all of our platforms in his capacity as content manager, including web content and other materials. Glen has witnessed the whole gamut of Sash Window Refurbish's window restoration activities, from our work on significant listed Georgian homes to a wide variety of smaller-scale private residential projects.


My technician Andrew replaced all my sash windows that had rotten sills. Accessing the rotten sills was not an easy task. He explained to me what needed to be done in order to fix the problem. He is a great person and I’m happy that he was the one who did the job. He is reliable, tidy, friendly and very professional. I highly recommend him.



I hired Andrew and Alex a while back to repair my damaged sash windows. They were was very considerate and very patient as he did his job. A few days ago, I had another problem with one of my sash lock keys and I called him again to come and fix the problem. I’m very impressed that Liam responded quickly and he not only fixed the problem but he also gave me a spare key. What a great after sales service!

Alan W.


I’m very impressed with the new windows that Andrew installed and also the reconditioning job that he did on other sash windows. The quality of his work is by far more superior than what we got when we hired another company a few years back. We will certainly hire him again if any window work arises

Kelly (Sleaford)


Our decorator referred us to Andrew because some of the work needed a window expert. Andrew together with our decorator did a fantastic job. The work was done efficiently and to the highest standards. Andrew is understanding, committed and very professional. I recommend him without any hesitation.

Steaven Reader


Alex did a great job in fixing windows in our terraced house. The windows were broken, frames damaged and the wood was also rotten. Alex's job was high quality and he did it pretty fast. I was also very impressed that he was considerate of my son’s asthma condition and maintained cleanliness. Top work.



Andrew just recently replaced three sash windows in my Edwardian house. He also repaired and replaced some sills and draught proofed three windows. In addition to that, he also did some carpentry work. What I like the most about Liam is that he did a clean job. He is very professional and always updated me about the timescales and costs. He also did his job with minimal disruptions. I highly recommend him.

Cris M.