Every glazier's brochure mentions argon gas as an upgrade option for double glazing. The pitch: argon is a denser gas than air, conducts heat less readily, and improves your IGU's U-value.
All of that is true. The question is by how much — and whether the improvement justifies the cost.
The Actual Thermal Difference
| Configuration | Typical U-value (W/m²K) |
|---|---|
| Standard clear IGU (air fill) | 2.7 – 2.9 |
| Standard clear IGU (argon fill) | 2.5 – 2.7 |
| Low-E + air fill | 1.8 – 2.0 |
| Low-E + argon fill | 1.4 – 1.6 |
The difference between air-fill and argon-fill is approximately 0.2–0.3 W/m²K for a standard clear IGU. On its own, that is a modest improvement.
Where argon becomes meaningful is in combination with a Low-E coating. Soft-coat Low-E with argon fill achieves U-values of 1.4–1.6 — a significant improvement over either component alone. The argon fill amplifies the Low-E coating's effectiveness by reducing convective heat transfer in the cavity.
Is Argon Worth the Premium on Its Own?
On a standard clear IGU without Low-E, adding argon fill typically costs $30–$60/m² and improves U-value by ~0.2 W/m²K.
For context: the thermal improvement from upgrading a single-pane window to any double glazing is a U-value change of ~3.0 W/m²K. Adding argon to a standard IGU adds ~0.2 W/m²K on top of that.
Verdict: Marginal. If you are not specifying Low-E, the argon premium is a low-value add. Spend that budget on the Low-E upgrade instead — it delivers 5–8× more thermal improvement per dollar.
Argon + Low-E: Worth It
The combination delivers real performance gains and is the recommended specification for Melbourne homes with significant heating and cooling costs. The incremental premium over hard-coat Low-E with air fill is typically $40–$70/m² for argon fill — justified by the resulting U-value of 1.4–1.6.
Long-Term Considerations
Argon slowly permeates through the IGU seal over time — an annual loss rate of approximately 0.5–1.0% per year is normal. After 20 years, an argon-filled unit may have closer to 80–90% argon. This is considered acceptable performance.
Importantly: when an argon-filled IGU's seal eventually fails, moisture ingress (fogging between the panes) is the first symptom — the same as an air-filled unit. There is no practical maintenance difference.
Summary
- Argon alone: modest benefit, low priority
- Argon + Low-E: meaningful, recommended for whole-home retrofits
- Standard IGU without either: good value if budget is a constraint; still dramatically better than single pane
See the Glass Types comparison page and the Low-E glass guide for full specification decisions.
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