Argon gas reduces heat transfer through insulated glass by approximately 30% over air at minimal cost. Krypton gas provides 40% better insulation than argon but costs significantly more. For most homes in the DC, Virginia, and Maryland area, argon delivers the best value. This guide covers thermal conductivity, density, optimal cavity widths, R-value improvements, and cost analysis for each gas.
Last Updated: March 2026
Physical properties and performance comparison of argon, krypton, and air as insulating gas fills in sealed glass units.
| Property | Argon (Ar) | Krypton (Kr) | Air (Reference) |
|---|---|---|---|
| Atomic Mass | 39.9 amu | 83.8 amu | 28.97 amu (avg) |
| Density | 1.78 kg/m3 | 3.75 kg/m3 | 1.29 kg/m3 |
| Thermal Conductivity | 0.016 W/mK | 0.0087 W/mK | 0.024 W/mK |
| Heat Reduction vs Air | ~30% | ~64% | Baseline |
| Optimal Cavity Width | 1/2 - 5/8 inch | 3/8 inch | 3/4 inch |
| R-Value Improvement | 15-20% over air | 30-40% over air | Baseline |
| U-Factor (dbl pane + Low-E) | 0.25 - 0.30 | 0.20 - 0.24 | 0.35 - 0.47 |
| Dissipation Rate | ~1% per year | ~0.5% per year | N/A |
| Natural Abundance | 0.93% of atmosphere | 0.0001% of atmosphere | 100% |
| Relative Cost | Low | High (10-20x argon) | Free |
| Best Application | Standard double/triple pane | Thin-profile triple pane | Economy windows |
Noble gases improve window insulation by reducing both conduction and convection within the sealed cavity. Their larger, heavier molecules move more slowly than air molecules, transferring less heat energy.
In the Washington DC metropolitan area (IECC Climate Zone 4A), argon gas with Low-E coating is the most cost-effective combination for residential windows.
Energy Star requires a maximum U-factor of 0.30 for Zone 4. Double-pane windows with argon gas and Low-E coating achieve U-factors of 0.25-0.30, meeting this requirement at the lowest cost. The additional investment in krypton gas would reduce the U-factor to 0.20-0.24, saving an additional 2-5% on energy bills -- typically not enough to justify the cost premium in the DMV's moderate climate.
The exception is homeowners pursuing Passive House certification or net-zero energy construction, where triple-pane krypton-filled windows with U-factors of 0.10-0.15 are specified. Contact Expert Glass Repair for a consultation on which gas fill is right for your project.
Argon and krypton are both inert noble gases used to fill the sealed cavity in insulated glass units (IGUs). Argon has a density of 1.78 kg/m3 and thermal conductivity of 0.016 W/mK, reducing heat transfer by approximately 30% compared to air. Krypton is denser (3.75 kg/m3) with lower thermal conductivity (0.0087 W/mK), reducing heat transfer by approximately 40% more than argon. The key practical difference is that krypton performs best in narrower cavities (3/8 inch or less) while argon performs best in wider cavities (1/2 to 5/8 inch).
In the DC, Virginia, and Maryland climate (IECC Zone 4), krypton gas is generally not cost-effective for standard residential windows. The incremental energy savings over argon are relatively small -- approximately 2-5% additional energy savings -- while the cost premium is substantial. Krypton makes financial sense primarily in triple-pane windows with narrow cavities, passive house construction targeting U-factors below 0.15, or high-performance commercial glazing where thin profiles are required. For most DMV homeowners, argon provides the best value.
Replacing air with argon gas in a double-pane window improves the center-of-glass R-value by approximately 15-20%. A standard double-pane window with air fill achieves approximately R-1.8 to R-2.0. Adding argon fill improves this to R-2.5 to R-2.7. Combined with a Low-E coating, the R-value reaches R-3.3 to R-4.0. The improvement is most significant in the center of the glass -- the overall window R-value (including frame and edge effects) is lower.
Yes, argon gas dissipates from insulated glass units at a rate of approximately 0.5-1% per year through the perimeter seal. A well-manufactured IGU starts with approximately 90-95% argon concentration and remains thermally effective as long as concentration stays above 80%. At 1% annual loss, an IGU maintains effective argon concentration for 10-15 years, after which performance gradually decreases toward air-filled levels. Seal failures can accelerate gas loss significantly. Krypton escapes at a slightly slower rate due to its larger atomic mass.
Technically, argon can be re-injected into an IGU through a small drilled hole that is then sealed, but this is rarely recommended. If the gas has escaped, it typically means the perimeter seal has failed, and simply refilling gas does not fix the underlying seal problem. The gas will continue to leak through the failed seal. Moisture may also have entered the unit, saturating the desiccant. In most cases, replacing the insulated glass unit is more effective and provides a new sealed system. Expert Glass Repair can assess whether re-gassing or replacement is appropriate.
Argon gas performs optimally in cavity widths of 1/2 inch to 5/8 inch (12-16mm). Below 3/8 inch, conduction through the narrower gas space offsets argon benefit. Above 3/4 inch, convection currents begin to circulate within the argon, reducing insulating performance. Krypton, being denser, performs optimally in narrower cavities of 3/8 inch (9-10mm). This narrower optimal width makes krypton ideal for triple-pane windows where total unit thickness must be minimized, and for slim-profile window designs.
No. Both argon and krypton are inert, non-toxic, non-flammable, odorless, and colorless noble gases. Argon makes up approximately 0.93% of Earth's atmosphere and krypton 0.0001%. If an IGU seal fails and gas escapes into a room, the quantities are too small to affect air quality or pose any health risk. A standard window IGU contains approximately 0.5-1 cubic foot of gas. Neither gas reacts with any materials in the window assembly. There are no safety concerns with either gas in residential or commercial applications.
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