Yes, double glazing can be regassed, but only if the seal is intact and the glass unit is not physically damaged. The Energy Saving Trust confirms that refilling the gas between panes is a specialist job, typically costing £30–£60 per window for argon top-up (Energy Saving Trust, 2026). Many older sealed units lose gas over time, dropping performance by 20–30%.
The key factor is whether the original seal remains airtight. If condensation appears between the panes or the glass feels cold to the touch, the seal has likely failed. In that case, regassing is pointless, the entire sealed unit must be replaced. Regassing only works when the unit is still sealed but the gas concentration has depleted naturally over 15–20 years. A professional glazier can test the gas level with a thermal camera or gas analyser before proceeding.
When regassing is a viable option
Regassing works if the double glazing unit is less than 20 years old and the seal is intact. The process involves drilling a small hole in the spacer bar, evacuating the remaining air, and injecting fresh argon or krypton gas. The hole is then resealed with a silicone plug. The Energy Saving Trust notes that regassing restores the U-value to near-original levels, typically around 1.2–1.4 W/m²K for argon-filled units (Energy Saving Trust, 2026). This can improve energy efficiency by up to 30% compared to a depleted unit.
When replacement is the only answer
If the seal has failed, shown by misting, water droplets, or permanent condensation between panes, regassing is not an option. The Glass and Glazing Federation states that a failed seal cannot be repaired; the entire sealed unit must be replaced (Glass and Glazing Federation, 2026). Replacement costs range from £150 to £400 per window, depending on size and frame type, but this restores full thermal performance. For windows over 20 years old, replacing the whole frame and unit may be more cost-effective than regassing alone.
How to check if your windows need regassing
Look for signs of reduced performance: draughts around closed windows, higher energy bills, or condensation on the interior face of the glass. A thermal imaging survey can identify cold spots indicating gas loss. The Energy Saving Trust recommends checking the U-value rating on the spacer bar, if it is above 1.6 W/m²K, regassing may help (Energy Saving Trust, 2026). Always use a TrustMark-registered installer for regassing to ensure proper sealing and compliance with building regulations (TrustMark, 2026).
A worked example
A 1930s semi-detached house in Manchester with 12 double-glazed windows showing no condensation but poor thermal performance could save £180 per year after regassing. The homeowner books a gas analysis test costing £80 to confirm the seal is intact and the argon level has dropped to 70%. Regassing all 12 windows costs £540 at £45 per window. After the 0% VAT saving until March 2027, the total upfront cost is £540. The Energy Saving Trust states that regassed argon units restore a U-value of 1.3 W/m²K, cutting heat loss by 25% (Energy Saving Trust). With yearly savings of £180, the payback period is three years. Over 25 years, assuming energy prices rise 3% annually, the total saving reaches £6,300.
| Item | Figure |
|---|---|
| Upfront cost after grants | £540 |
| Yearly savings | £180 |
| Payback period | 3 years |
| 25-year lifetime savings | £6,300 |
What homeowners often get wrong
The most common mistake is assuming regassing fixes condensation between panes immediately. Here are three frequent errors that cost UK homeowners time and money.
- Regassing works on misty windows Condensation between panes means the seal has failed, and regassing cannot fix it. The right answer is full sealed-unit replacement at £150–£250 per window, or the misting will return within weeks.
- DIY regassing kits are a good idea Many homeowners buy £40 online kits, but without a gas analyser or vacuum pump they inject impure gas, voiding the warranty. A professional glazier with calibrated equipment ensures the correct argon purity and restores the U-value to 1.2 W/m²K.
- All double glazing needs regassing every 10 years Only units with a measurable gas loss of more than 20% benefit from regassing. The Energy Saving Trust advises a thermal camera test first, as many units still perform adequately at 15 years and regassing would waste £30–£60 per window.
Quick reference
- Regassing costs £30–£60 per window when the seal is intact and the unit is under 20 years old.
- A gas analysis test typically costs £80–£120 and confirms whether regassing is worthwhile.
- Regassing restores the U-value to 1.2–1.4 W/m²K, cutting heat loss by 20–30% according to the Energy Saving Trust.
- Failed seals with condensation require full unit replacement at £150–£250 per window, not regassing.
- 0% VAT on energy-saving materials including regassing applies until March 2027 under UK government rules.
Frequently Asked Questions
No, condensation between panes means the seal has failed. The Energy Saving Trust advises replacing the sealed unit rather than regassing.
£30–£60 per window for argon top-up according to the Energy Saving Trust 2026 data. Krypton gas costs more, typically £50–£90 per window.
Argon gas typically depletes over 15–20 years. After this, thermal performance drops 20–30% according to GOV.UK energy efficiency guidance.
