How do double-glazed windows reduce energy transfer?

Double-glazed windows reduce energy transfer by trapping air between two glass panes, minimising heat loss and gain.

Double-glazed windows consist of two layers of glass with a gap of air or inert gas like argon between them. This design is highly effective in reducing energy transfer through conduction, convection, and radiation. The air or gas trapped between the panes acts as an insulating barrier. Air and gases like argon are poor conductors of heat, so they significantly slow down the rate at which heat can pass through the window.

In terms of conduction, the double layers of glass and the insulating gap reduce the amount of heat that can be transferred directly through the window material. Since glass is a better conductor of heat than air or argon, the presence of the gas-filled gap means that less heat is conducted from the warm side to the cool side.

Convection is also minimised in double-glazed windows. In a single-glazed window, air can circulate freely, transferring heat from the warm side to the cool side. However, in double-glazed windows, the gap between the panes is too narrow for significant air movement, which reduces heat transfer by convection.

Radiation is another form of energy transfer that double-glazed windows help to reduce. The two layers of glass can be coated with low-emissivity (low-E) materials that reflect infrared radiation. This means that heat from inside the house is reflected back into the room, while heat from the sun is reflected away, keeping the interior cooler in summer and warmer in winter.

Overall, double-glazed windows are an effective way to improve energy efficiency in homes, reducing the need for heating and cooling systems and thereby saving energy and reducing utility bills.