No, double glazed windows should not feel cold on the inside under normal conditions. A properly installed double glazed unit should maintain an internal surface temperature close to room temperature. The Energy Saving Trust states that modern double glazing typically has a U-value of 1.2 to 1.4 W/m²K, which significantly reduces heat loss compared to single glazing (Energy Saving Trust, 2026). If the inner pane feels cold to the touch, it suggests a performance issue.
Whether your windows feel cold depends on the temperature difference between the room and the outside. On very cold days, even efficient double glazing may feel slightly cool. But persistent coldness indicates a problem with the seal, the glass, or the frame. This affects homes of all ages, but is most common in older double glazing installed before 2002, when U-values were higher. The issue does not apply to triple glazing, which has even better thermal performance.
Failed seals cause cold spots
A failed seal between the two glass panes allows moisture or argon gas to escape. This reduces the insulating gap, making the inner pane colder. The Glass and Glazing Federation says a failed seal often leads to condensation between the panes (Glass and Glazing Federation, 2026). You can check by looking for misting or water droplets inside the unit. If present, the window needs replacing. A typical replacement double glazed unit costs £200–£400 per window, according to the Energy Saving Trust (Energy Saving Trust, 2026).
Poor installation or frame issues
Cold feeling windows can also result from gaps around the frame or poor installation. FENSA registered installers must comply with building regulations, which require a maximum U-value of 1.6 W/m²K for replacement windows (FENSA, 2026). If your windows meet this standard but still feel cold, check for draughts around the frame. Draught-proofing strips can reduce heat loss by up to £125 per year, says the Energy Saving Trust (Energy Saving Trust, 2026).
Low-E coating or gas fill degradation
Modern double glazing uses low-emissivity (low-E) coatings and argon gas fill to improve insulation. Over time, the gas can leak, reducing the window’s U-value by 10–20%. The Building Research Establishment notes that argon-filled units have a U-value around 1.2 W/m²K, compared to 2.0 W/m²K for air-filled units (BRE, 2026). If your windows are over 15 years old, the coating may have degraded. A thermal imaging survey can identify cold spots, costing £100–£200. Replacing old units with new A-rated double glazing can save £110–£155 annually on heating bills, per the Energy Saving Trust (Energy Saving Trust, 2026).
A worked example
Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6). The existing windows are 18 years old with a U-value of 2.8 W/m²K, causing the inner panes to feel cold in winter. Replacing them with modern A-rated double glazing (U-value 1.2 W/m²K) saves approximately £195 per year on heating bills, according to the Energy Saving Trust. The payback period is under eight years, and over 25 years the total saving reaches £4,875. If your household qualifies for ECO4, the entire cost may be covered, making the upgrade effectively free.
| Item | Figure |
|---|---|
| Upfront cost after grants | £1,500 |
| Yearly savings | £195 |
| Payback period | 7.7 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming that any coolness on the inner pane means the window has failed. Here are three misunderstandings that cost homeowners money and comfort.
- Thinking a cold pane always means a broken seal On a day when the outside temperature drops below -5°C, even well-insulated double glazing can feel slightly cool to the touch. The real test is condensation between the panes or a visible mist that does not wipe away. A failed seal leads to trapped moisture and a permanent cold spot, which reduces the window’s U-value by up to 40% and voids your warranty.
- Believing all double glazing is the same Windows installed before 2002 typically have a U-value above 2.0 W/m²K, while modern units achieve 1.2 to 1.4 W/m²K. Replacing old windows with current standards can cut heat loss by half, saving £150 to £250 per year for a typical semi-detached home. Sticking with old glazing means you are paying £12 to £20 extra each month on your heating bill.
- Ignoring the frame and installation quality A cold inner pane often comes from draughts around the frame rather than the glass itself. Poorly fitted frames or degraded seals let cold air bypass the glazing, creating a chill that the window unit cannot fix. This mistake costs you the full replacement price of the glass without solving the problem, and it can also invalidate your building warranty if the installation was not certified by a FENSA or CERTASS scheme.
Quick reference
- A double glazed window with a U-value of 1.2 W/m²K should feel close to room temperature on a typical UK winter day.
- Condensation between the glass panes is the clearest sign of a failed seal and usually means the whole unit needs replacing.
- Your home may qualify for a free or heavily subsidised replacement under the ECO4 scheme if your total household income is below £31,000.
- Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6).
- A cold inner pane that appears dry and clear is often caused by a draughty frame, not the glass itself.
Frequently Asked Questions
A cold inner pane usually means the seal has failed or the U-value is too high. The Energy Saving Trust says modern double glazing should have a U-value of 1.2 to 1.4 W/m²K.
On very cold days, double glazing may feel slightly cool, but not persistently cold. The Glass and Gazing Federation warns that persistent coldness points to a performance issue.
Look for misting or water droplets between the glass panes. The Glass and Glazing Federation confirms this indicates a failed seal, requiring replacement.
