Select New Efficient Replacement Windows

5. Select the most efficient windows for your specific house

Apart from the local climate, consider the following factors for selecting the most energy-efficient windows for your home:

• Orientation and shading conditions
• Heating and cooling system
• Your personal preferences and habits

Orientation and shading conditions

The preferable solar heat gain coefficient (SHGC) depends not only on the climate, but also on window orientation and shading conditions. South-facing windows are well-suited to invite beneficial solar heat in the winter and can often be shaded from the high summer sun. East- and west-facing windows, on the other hand, tend to receive more sunshine in the summer than in the winter, and are therefore likely candidates for unwanted solar heat gain. Any windows, including north-facing windows, can receive solar heat from reflective surfaces such as asphalt or neighboring façades, or may be shaded by trees or buildings.

ENERGY STAR criteria limit the SHGC in warm climates but still leave you a choice among options such as moderate-solar-gain and low-solar-gain low-E coatings. In cold climates, ENERGY STAR criteria allow the whole SHGC range. If different sides of your house could benefit from different levels of solar heat control, you may possibly want to consider varying the SHGC levels among your windows.

Heating and cooling system

Reduced heating and cooling demand from upgraded windows may allow for smaller heating and cooling equipment. Consequently, when equipment is replaced, it is worth accounting for the effect of the more energy-efficient windows. Smaller equipment costs less, which may offset part of the window upgrade cost. What is more, equipment that is downsized according to reduced demand does a better job at keeping the home healthy and comfortable because it runs more evenly than oversized equipment.

Heating and cooling equipment is often larger than needed, and energy-efficient windows reduce the demand even further. Low window U-factors reduce peak heating loads, a low SHGC reduces peak cooling loads. The peak load for a building is the maximum requirement for heating or cooling at one time. See here how different window types can impact peak loads in a typical house. The optimum size for equipment in your house should be determined by technicians using detailed computational procedures (e.g. ACCA Manual J) that take into account window U-factor and SHGC, window orientation, overhangs, internal shades, etc.

Proper sizing calculations for your next heating and cooling equipment changes will help you avoid stop-and-go cycles, typical for oversized equipment that impact the ability of air conditioning to dehumidify. And the cost savings from smaller equipment may balance part of the cost of high efficiency windows.

Personal preferences and habits

Personal preferences and habits matter for choosing energy-efficient windows. If, in response to hot sun, you and your family are more likely to turn on the AC than pull the shades, a low SHGC promises more comfort and lower cooling cost. If you can deal with solar heat gain just fine, a higher SHGC may help you save heating cost. Low U-factor and low air leakage are particularly important if you spend much time sitting close to the windows, where cold glass and drafts would affect your comfort.

Depending on your preferences, you may want to take into account the following issues that can be addressed with energy-efficient windows:

• Winter and summer comfort
• Condensation resistance
• Daylight and view
• Fading protection

For more comprehensive information on how different levels of window performance affect comfort, condensation and seasonal energy use, download the EWC Multiple Benefits Fact Sheet.

To fully benefit from energy-efficient windows, look for durable products and ensure proper installation.

6. Some guidance on window durability»

7. Ensure proper installation»