Two or more panes
Multiple layers create enclosed spaces and allow coatings or laminated safety makeups where specified.
Plain-Language Insulated Glass Guide
What Is a Window Sealed Unit?
A sealed unit is the removable insulated glass assembly inside many modern window sashes—not the entire frame, trim or operating window.
Glass Built as One Assembly
Two or more panes are joined at the edge by a spacer and perimeter seals
A window sealed unit is also called an insulated glass unit, IGU, double glazing or thermopane. Panes are separated by a spacer to create one or more enclosed cavities, then sealed around the perimeter so the assembly can be installed into a sash or fixed frame.
The spacer may contain desiccant that manages small amounts of residual moisture from manufacturing. Depending on the specification, the cavity may contain air or gas, and one pane may have a Low-E coating. Grids can be placed between panes.
The sealed unit does not include the complete vinyl, wood, aluminum or composite frame. That distinction is why glass-only service can sometimes preserve the existing window.
Know the Main Parts
Pane, spacer and perimeter seal form the insulated assembly
Visible glass is only the centre of a sealed unit.
Edge spacer
The spacer maintains separation and may contain desiccant; its width contributes to overall unit thickness.
Perimeter seal system
Edge seals keep the cavity isolated and bond the assembly so it can perform as one component.
Sealed-Unit Basics
Answers that clarify repair terminology
Is a sealed unit the whole window?
No. It is the insulated glass assembly held by a sash or frame. Locks, cranks, balances, weather seals, screens and trim are separate components.
What is inside the space between panes?
Depending on the specification, the cavity may contain dry air or an insulating gas. The exact original fill cannot be identified from appearance alone.
Where is the Low-E coating?
Low-E is a thin surface coating placed on a protected pane surface according to the glass design. Its position and type affect performance and appearance.
Why do sealed units become foggy?
When edge-seal integrity is lost, moisture can enter the cavity and create recurring haze, droplets or staining between panes.
Can one sealed unit be custom made?
Often, yes, when final dimensions, thickness, coatings, grids, spacer and safety requirements can be established and the frame remains serviceable.
What stays during glass-only replacement?
The existing sash or fixed frame, operating hardware, screen and surrounding trim usually remain unless the written scope identifies additional work.
Replace the Unit or the Window
A failed component does not automatically condemn the opening
Glass failed but support remains sound
A custom IGU can restore clarity while retaining the existing sash and frame.
- Serviceable glazing stops
- Stable frame and sash
- Known glass specification
The supporting system is also failing
Renew the complete opening where distortion, rot, leakage or operation makes glass-only work incomplete.
- Frame cannot support new unit
- Water damage extends beyond glass
- Multiple components need correction
Specification Matters
Same size does not mean same glass
Overall thickness, pane type, coatings, tint, spacer, gas fill, grids and safety location can all change the correct order. Final service measurements and markings are important.
A technically compatible new unit can still look different beside older glass. Discuss tint, reflection, grids and spacer colour before fabrication.
Continue the Research
Move from definition to diagnosis
Identify the Component Before Pricing It
Request a Repair AssessmentNeed a sealed unit measured in Hamilton?
Send Windows Hamilton a full-window photo, close-ups of spacer markings and the visible problem. We will help confirm whether the request is for an IGU, another window component or complete replacement.
Talk with our team: Call Windows Hamilton at 289-975-4020.