To tell the age of your windows, check the spacer bar between the glass panes for an etched date. If there’s no marking, look for manufacturer labels on the frame, check old paperwork, or contact the installer if known.

You’re thinking of purchasing a new home, but the windows look a little tired.. How can you tell their age and whether they’ll need replacing soon? Double glazing doesn’t last forever, and knowing when it was installed can help you plan your home renovation budget. In this guide, we’ll show you how to date your windows and spot signs they might need replacing.

How to Check the Age of Your Double Glazing

Over time double glazing can lose its efficiency, leading to draughts, condensation and more importantly rising energy bills! Now in 2025, no one needs higher energy bills, are we right?!

There are a few simple ways that we check the age of windows when we turn up at a job, and in this guide we will outline the 5 simple steps for you to be able to do the same. 

Step 1 – Check the Spacer Bar for a Date Stamp

Many double glazing units have a manufacturing date etched onto the metal spacer bar, which sits between the two panes of glass. To find it, inspect the edge of the glass where the spacer bar runs along the inside of the frame. The numbers may include details such as the manufacturer, glass specifications, and the year of production.

If you spot a date, this indicates when the sealed unit was made, though the actual installation could have been slightly later. If there’s no visible marking, don’t worry there are other ways to determine the age of your windows.

Step 2 – Look for Manufacturer Labels or Stamps

Some window manufacturers include branding, serial numbers, or certification marks on the frame. Check the inside edge of the window, near the hinges, or along the bottom of the frame for stickers, engraved markings, or small plaques.

These labels often contain useful details such as the manufacturer’s name, product code, and sometimes even the production year. If you find a brand name, you can look up the company’s records or contact them to confirm the installation date.

Step 3 – Check Old Paperwork or Warranty Documents

If you have access to any paperwork related to the property, check invoices, receipts, or warranty documents for details about the window installation. Many double glazing companies provide guarantees that last between 10 to 20 years, often with the installation date recorded.

Look for certificates from schemes like FENSA or Certass, as these confirm compliance with building regulations and typically include the installation date. If you don’t have physical copies, you may be able to check online using the property’s postcode.

Step 4 – Contact the Installer or Manufacturer

If you know which company installed the windows, they may have records of the installation date. Many double glazing companies keep details of past work, especially if they provided a warranty or guarantee.

If you found a manufacturer’s name on the spacer bar or frame, try contacting them with any serial numbers or markings you’ve found. Some manufacturers can provide information on when the windows were produced and may even be able to confirm the installation date if they worked with a specific installer.

Step 5 – Assess the Condition of the Windows

If you can’t find any records, the physical condition of your windows can give you clues about their age. Look out for common signs of aging, such as:

  • Condensation Between the Panes – This indicates the seal has failed, which usually happens after 10–20 years.
  • Draughts or Poor Insulation – Older windows lose efficiency over time, making your home feel colder.
  • Discoloured or Warped Frames – UPVC can yellow, wood may rot, and aluminium might corrode as the years pass.
  • Stiff or Faulty Hinges & Locks – If opening and closing your windows is a struggle, they may be reaching the end of their lifespan.

While these signs don’t give an exact installation date, they help determine whether your double glazing is due for replacement. With step 5 it is very much an opinion, and while a professional’s opinion could be fairly accurate, for most homeowners this would not be an accurate way to find the age of your windows. 

Is It Time to Replace Your Double Glazing?

If your windows are showing signs of wear or you’ve discovered they’re decades old, upgrading to modern double glazing can improve energy efficiency, security, and comfort in your home. At Swallow Glazing, we offer expert window replacements tailored to your needs.

Get in touch today for a free consultation and find out how we can help you upgrade your home’s windows.