Sealed unit replacement
Sealed units made to your sizes, supply only or fitted.
A sealed unit is two or three panes bonded to a spacer bar with a desiccant inside and a gas fill between. It is a manufactured component, and it is replaceable on its own — the frame it sits in is a separate thing entirely.
People replace units for three reasons: the seal has failed and it has misted, the glass has broken, or they want better performance from the same window.
How to measure a sealed unit
Measure the glass, not the frame — width, height, and overall thickness. If the unit is still in place, measure the visible glass and add roughly the amount hidden under the bead on each edge, or take the bead off and measure properly. If you are ordering supply only, get this right: a unit 4mm too big does not go in.
Specification worth choosing
- Low-E coating — reflects heat back into the room. Standard now, always worth it.
- Argon fill — denser than air, conducts less heat.
- Warm edge spacer — a non-metal spacer that cuts the cold bridge at the glass edge.
- Toughened — required in critical locations.
- Laminated — security, and it holds together when broken.
- Acoustic — an asymmetric build plus a damping interlayer, for road noise.
Supply only or fitted
Supply only is much cheaper and perfectly reasonable if you can take a glazing bead off and put it back. Fitted makes sense on anything large, high up, or where the beads are external and awkward. Both are priced separately so you can choose.
A photograph is worth ten minutes on the phone. Send one on WhatsApp and we will tell you what it is and what it costs.
Questions
How long does a sealed unit last?
Typically 15 to 25 years. South and west elevations fail sooner because the seal is worked harder by daily heating and cooling.
Can I replace just one pane of a double glazed unit?
No. The unit is bonded as one component — both panes and the spacer come as a set.
Do I need the same thickness as the old one?
Yes, or the beads will not hold it and it will not seal. Measure the overall thickness of the existing unit before ordering.
Will a new unit look different to the others?
Slightly, sometimes. Modern coatings have a marginally different tint to a 20-year-old unit. In one window among several it is rarely noticeable.
Is it notifiable work?
No. Replacing glass in an existing frame is a repair and does not need building regulations notification.