Yes, you can regas double glazed windows, but it is rarely cost-effective and only works if the seal is intact. The Energy Saving Trust confirms that replacing the entire sealed unit is usually more practical than regassing alone (Energy Saving Trust, 2026). Expect to pay £30–£80 per window for professional regassing, versus £100–£250 for a new sealed unit.
The key factor is whether the argon or krypton gas has actually leaked out. If the seal has failed, regassing will be ineffective because the gas will escape again. A failed seal is indicated by condensation between the panes, misting, or a visible gap. Regassing only makes sense for windows with a working seal but degraded gas performance, typically older units where the gas has diffused slowly over 10–20 years.
Regassing only works on intact seals
Before considering regassing, check for seal failure. The Gas Safe Register notes that a broken seal means gas loss is permanent and regassing cannot fix it (Gas Safe Register, 2026). If you see condensation, fogging, or draughts, the seal is compromised. In such cases, the only effective solution is replacing the entire sealed unit or the whole window. Regassing a failed seal wastes money, the gas will escape within weeks.
Professional regassing costs from £30 per window
A specialist can regas a standard double-glazed unit for £30–£80 per window, according to TrustMark-registered installers (TrustMark, 2026). This involves drilling a small hole, inserting a valve, and injecting argon or krypton gas. However, the process is labour-intensive and not all window types are accessible. For most homes, replacing the sealed unit costs £100–£250 and includes new gas, a new seal, and a warranty. Regassing rarely offers a payback period under 10 years.
DIY regassing kits are not recommended
DIY regassing kits are available online for £20–£50, but the Energy Saving Trust advises against them (Energy Saving Trust, 2026). These kits typically use low-pressure valves that cannot restore the original gas concentration. Professional regassing achieves around 85–90% gas fill, while DIY kits often manage less than 50%. For a typical double-glazed window, the energy saving from regassing is only 2–5% on heating bills, far less than replacing a failed unit entirely.
A worked example
A typical 1930s semi-detached house in Manchester with 12 double-glazed windows showing condensation between the panes would cost roughly £2,400 to replace all sealed units at £200 each. After checking with a MCS-certified installer, you discover only two windows have a failed seal, the rest have intact seals but have lost their argon gas over 20 years. Regassing those ten windows at £50 each costs £500, while replacing all twelve units costs £2,400. The Energy Saving Trust confirms that regassing intact units can restore thermal performance to near-original levels, saving up to £150 per year on heating bills compared to leaving them unrepaired Energy Saving Trust. Payback on the regassing is just over three years, versus never if you replace units that didn’t need replacing.
| Item | Figure |
|---|---|
| Upfront cost after grants | £500 (regassing ten windows) |
| Yearly savings | £150 |
| Payback period | 3.3 years |
| 25-year lifetime savings | £3,250 |
What homeowners often get wrong
The most common mistake is assuming regassing fixes condensation between the panes. Here are three frequent errors that cost homeowners time and money.
- Confusing condensation with gas loss Condensation or misting between panes means the seal has failed, not that the gas has simply degraded. Regassing a window with a broken seal wastes £30–£80 because the new gas will leak out within weeks, and the condensation will return.
- Thinking regassing is a DIY job Buying a DIY regassing kit for £20–£40 seems cheaper than a professional, but the Gas Safe Register warns that incorrect pressure or valve placement can void your window warranty and reduce thermal performance by up to 30%. A professional regas costs £30–£80 and includes a pressure test.
- 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). This saves £40–£100 on a typical replacement job, but only if you use a registered installer.
Quick reference
- Regassing costs £30–£80 per window professionally, while a new sealed unit costs £100–£250 including installation.
- A failed seal is confirmed by condensation, misting, or visible draughts between the panes, regassing cannot fix this.
- The Energy Saving Trust states that argon gas diffuses slowly over 10–20 years, so older windows with intact seals may benefit from regassing.
- Replacing all sealed units in a typical three-bed semi costs £1,200–£3,000, compared to £360–£960 for regassing ten windows.
- DIY regassing kits void most manufacturer warranties and often fail to restore full thermal performance, costing more in the long run.
Frequently Asked Questions
Professional regassing costs £30–£80 per window, according to TrustMark-registered installers. Replacing the sealed unit ranges from £100–£250.
No, condensation between panes means the seal has failed, and regassing will not work. The Energy Saving Trust recommends replacing the entire sealed unit instead.
Yes, regassing can restore insulation if the seal is intact and the gas has degraded over 10–20 years. The Gas Safe Register confirms it is only effective on units with a working seal.
