Do you understand
Conduction and Convection?

Understanding the principles of conduction and convection is essential before any window purchase.

The more windows, the more important it becomes!

One of the ways heat passes through windows is by conduction.

Imagine you’re holding a hot coffee mug in your hand. The outside of the mug will feel warm because heat from the coffee passes through the solid mug.

This is conduction; the passage of heat through a solid material from molecule to molecule. If the mug is a tin cup, you will not be able to hold it for long because metal transfers heat more quickly than ceramic or foam.

This same principle applies to windows. Heat passes through the glass and frame. The composition of the window will determine how quickly the heat passes through.

Window insulation is also affected by another heat transfer mechanism called convection. Convection is the transfer of heat by the movement of gases or liquid.

As warm air inside a building comes in contact with a cold window, it cools and sinks, creating a convection current of air near the window. On the outside, wind blows against the glass.

In both cases, this air movement on the surface of the glass disturbs the air next to the glass, which is a component of the windows insulating value.

Still air is a good insulator, but moving air is not, so convection currents cause quicker conduction of heat through the window.

Conduction is driven by temperature differences.

When there is a difference in temperature from one side of the window pane to the other, heat will transfer through the glass and frame.

Heat transmission increases when there is a greater temperature difference between the inside and outside.

At Green Energy Windows we have vastly improved our product’s insulating value by only supplying double glazed windows, Low-E coatings, warm edge spacers and improved frame materials such as our composite and vinyl ranges.

All of these slow down the conduction of heat through the windows.

Installers can help maintain the resistance to conduction by installing the window or door in such a manner that the entire building’s weather barrier is continuous, with no air leakage. Problems associated with conduction and convection

• Heat loss in winter
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Heat gain in summer
• Discomfort felt by occupants sitting near a cold surface in winter (often misperceived as draftiness)
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Condensation on the product caused when warm house air contacts a cold window or door surface in winter
• Higher utility bills

Rating insulation value

• Insulating value is rated in terms of U-factor, which indicates the rate (how quickly) heat flows through a product for each degree of temperature difference between one side and the other.

The whole product U-factor accounts for heat flow through the entire assembly, including the frame.

This is important to consider, as the glass edges and frame usually have higher U-factors (faster heat transmission) than the centre of the glass and is the reason that warm edge spacers are also critical.

The lower the U-factor, the greater a window’s resistance to heat flow and the better its insulating value.

• Reducing conduction and convection

• The climate where the products will be used must be considered. The lower the U-factor, the greater the energy savings will be.

Lower U-factors result in improved energy efficiency in both summer and winter.

However, in very hot climates, blocking solar heat gain can be more important for keeping the home cool in summer.

You can be assured that at Green Energy Windows we have always had Conduction and Convention as a high priority and know that you will be delighted in the performance results of our windows.

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