Old windows can have a lot of charm, but they’re often one of the biggest culprits for heat loss in a home. Whether you live in a period property or a more modern build, upgrading old windows can make a noticeable difference to both your comfort and your energy bills.
Where Does the Energy Go?
In older single-glazed or poorly sealed windows, heat escapes through:
- Thin or single glazing – no insulation barrier
- Gaps and draughts – especially in sash or casement frames
- Warped timber or worn seals – reducing thermal performance
According to the Energy Saving Trust, up to 20% of a home’s heat can be lost through inefficient windows.
Potential Savings
How much you save will depend on your property type, the state of your current windows, and the upgrade you choose:
- Slimline double glazing in sash windows – can save £150–£250 per year on heating for a typical semi-detached home.
- Vacuum glazing in heritage frames – offers insulation close to triple glazing while preserving your window’s original style.
- Professional draught proofing – can cut heat loss by up to 15%, often for a fraction of the cost of full replacement.
For example, one SM Sashes customer in Chelmsford upgraded original sash windows with heritage slimline double glazing and draught proofing. The result? Their winter gas usage dropped by around 18% compared to the previous year.
Other Benefits Beyond Energy Savings
- Improved comfort – no more cold spots by the window
- Noise reduction – modern glazing reduces outside noise
- Added value – efficient homes are more attractive to buyers
- Lower carbon footprint – reduced energy use means fewer emissions
Choosing the Right Upgrade
Not all upgrades are the same. For period and listed properties, heritage glazing options like slimline or vacuum glass maintain the original look while delivering modern performance. For more modern timber windows, a full replacement with new double-glazed sashes may be the most effective route.
Bottom line:
Upgrading old windows isn’t just about aesthetics — it’s a smart investment in your home’s comfort, efficiency, and long-term value. If you’re ready to explore your options, SM Sashes can help find the perfect