When a window is leaking, it can mean two different problems. Air may be getting in around the window, which feels like a draft. Water may be getting into the wall or onto the sill after rain. This guide helps you decide whether to replace glass or window based on where the leak starts. The right fix depends on finding the true source first, then choosing between glass-only replacement and full window replacement. The goal is comfort, energy savings, and preventing damage to your home.
What Leaky Can Mean
Air Leaks
- Drafts around the frame or sash.
- Higher heating or cooling costs.
- Rattling or whistling in wind.
Water Leaks
- Water stains on drywall or the sill.
- Swollen trim, peeling paint, or mould.
- Puddles after wind-driven rain.
Step 1: Find The Source
Quick Checks You Can Do
- Hold a tissue near the frame and sash on a windy day to spot drafts.
- Look for cracked glass or fogging between panes.
- Check for fresh stains after rain at the head and sill.
- Open and close the window to see if it sticks or does not latch square.
What A Professional Will Look For
- Failing exterior caulking and missing or incorrect flashing.
- Rot, warping, or out-of-square frames.
- Insulated glass unit seal failure.
- Signs that water is entering from the wall above, not just at the window.
When Glass-Only Replacement Makes Sense
Glass-only replacement means swapping the insulated glass unit while keeping the existing frame and sash. It is most useful when the problem is inside the glass, not the frame or installation.
Choose This When
- The glass is cracked or fogged, but the frame is solid.
- There is no staining or swelling around the opening.
- The window operates smoothly and seals well.
- You want a quick fix with limited interior or exterior finishing work.
Benefits
- Lower cost than a full unit.
- Faster and less disruptive.
- Option to upgrade to low-e coatings, laminated glass, or privacy glass.
Limits
- Does not address frame problems or poor installation.
- Does not improve worn hardware or weatherstripping.
- Energy efficiency gains are limited by the performance of the existing frame.
- Matching the grid or divider bar width and profile on only one panel can be difficult. If an exact match is not available, replace both panes in the same opening so the grids match each other.
When Full Window Replacement is Smarter
Full replacement means removing the old unit and installing a new window with new frame, sash, and glass. This addresses problems at the frame, flashing, and installation.
Choose This When
- Drafts or leaks are at the frame or sash, not just the pane.
- There are water stains, swelling, rot, or mould around the opening.
- The unit is warped, out of square, or hard to operate.
- Leaks return after touch-ups to caulking.
- You want a larger upgrade in comfort and energy performance.
- The windows are very old or single-pane.
Benefits
- Best chance to stop water entry and drafts.
- New frame, weatherstripping, and hardware for smooth operation.
- Significant jump in energy performance and comfort.
- New warranty on the complete unit.
Trade-offs
- Higher cost.
- More time and finishing work.
- May require exterior trim or siding adjustments.
Pros and Cons At a Glance
| Option | Pros | Cons |
|---|---|---|
| Glass-only replacement | Lower cost. Quick. Keeps existing look. Upgrade glass type. | Does not fix frame, flashing, or installation. Limited efficiency gain. |
| Full window replacement | Comprehensive repair. Best leak control. Major efficiency and comfort improvement. New full-unit warranty. | Higher cost. More disruption. May need finishing work. |
Decision Flow: When to Replace Glass or Window
- Identify whether the issue is air or water.
- If there are stains, swelling, or rot around the opening, lean to full replacement.
- If the frame is solid and only the glass is cracked or fogged, consider glass-only.
- If the window sticks, does not latch, or is out of square, choose full replacement.
- If the budget is tight and problems are minor, you can stage work by priority.
- If the source is unclear, get a professional assessment that checks flashing and framing.
- If you need the highest-certainty fix, confirm the leak originates at the window assembly. A full replacement with new flashing integrated into the wall’s weather-resistant barrier offers the best chance to stop window-origin leaks. If water is entering from the wall, roof, or deck above, repairs to those areas are required; window work alone will not stop the leak.
Summary
Start by confirming whether the leak is air or water. Glass-only replacement is a targeted fix for cracked or fogged panes when the frame is sound and the window operates properly. Full window replacement is the reliable choice for leaks at the frame, staining, rot, or poor operation, and it offers the best path to long-term comfort and efficiency. Use the decision flow to choose with confidence and to know when to replace glass or window for a consistent, long-lasting result.
