What type of gas is commonly used to fill the space between double and triple pane windows to enhance energy efficiency?

The type of gas commonly used to fill the space between double and triple pane windows to enhance energy efficiency is argon. Argon is a colorless, odorless, non-toxic gas that is denser than air, which helps reduce heat transfer between the panes of glass. By using argon, the overall thermal performance of the window is improved, as it minimizes the conduction of heat, thereby helping to keep the interior of a building warmer in the winter and cooler in the summer. This contributes to better energy efficiency and can lead to lower heating and cooling costs.

In contrast, the other gases listed are less effective for this purpose. Oxygen is not commonly used since it is a reactive gas that could lead to corrosion within the window unit. Nitrogen, while it has some insulating properties, is not as effective as argon for reducing heat transfer. Carbon dioxide is not used for insulation in windows because it has a higher thermal conductivity compared to argon and does not provide the same energy efficiency benefits.