Why buy high performance windows? Created with efficient design and high-quality materials, having the most energy efficient windows installed can save massive amounts of both energy and money. According to the US Department of Energy, windows may be responsible for as much as ten to twenty-five percent of energy costs. In cooler weather, the problem is the loss of heat energy, in warmer weather, the problem is solar heat entering the home. Energy Star ratings have provided consumers with a guide for purchasing the best replacement windows possible for each climate zone.
Energy Star Standards for High Performance Windows
What makes Energy Star replacement windows different from outdated models? When a product comes with the Energy Star sticker, it is guaranteed to have met specific guidelines determined by the Department of Energy. Energy Star high performance windows are tested by the independent agency, the National Fenestration Rating Council to give each new model its specific ratings.
In general, these windows are made with at least two panes of glass. Having two, three, or four panes of glass, either empty, or filled with a non-toxic gas such as krypton, provides extra insulation. They must be constructed with high-quality framing material, such as fiberglass or vinyl. Energy Star windows are usually coated to reflect both infrared and ultraviolet light. This helps to keep heat inside in the winter, and outside in the summer. They are also manufactured with warm edge spacers in order to keep glass panes separated.
Energy Star Ratings
High performance windows are rated according to four different criteria. The U-factor, the solar heat gain coefficient (SHGC), air leakage, and visible transmittance (VT). The first two are the primary factors; air leakage and VT are secondary, and do not have to be listed on all labels.
- U-factor explains the rate that non-solar heat flows through the window. This figure reflects the overall performance, due to framing, coatings, and design. The most energy efficient windows have lower figures.
- SHGC represents the solar energy that enters the home through the window. Depending on geographic region, either a lower or higher number may be desirable.
- Air leakage represents the rate at which air is able to flow around a product. A low number means a tighter, and more practical window.
- VT is the amount sunlight which is visible to the human eye, that is transmitted through the glass panes and glazing.
The Most Energy Efficient Windows in Cooler Climates
In cooler climates, the most energy efficient windows will be those that keep the cold air outside and have minimal air leakage. The goal is to reduce the need for heat energy, by protecting the indoors from cold winter air, and sealing in and absorbing warm air. This means that very low U-factor and air leakage figures on the Energy Star label are ideal. For example, in the northern climate zone, the U-factor rating for high performance windows should be less than or equal to .3; in the north-central climate zone, it should be less than or equal to .32. Likewise, the lowest air leakage figure indicates the greatest quality for cooler climates.
As the SHGC and VT have to do with sunlight, both visible rays and heat energy, entering the home, a higher number may be desirable. For example, in the northern climate zone, the SHGC should be greater than or equal to .35. Determine individual climate zone by looking at the Energy Star informational website.
The Best High Performance Windows in Warmer Climates
In warmer climates, the goal is to reduce the need for cooler air by protecting the indoors from warm summer days, and the heat and glare of sunlight. The U-factor is still important, as cool air should not be leaking through the window. In the south-central climate zone for example, a figure less than .35 would be fine. In the southern climate zone, Energy Star replacement windows can have a U-factor of up to .6.
SHGC is the most important figure in mild and warmer areas. It is important that the amount of heat, entering the home as sunlight, be minimal. In the south-central climate zone, this figure should be less than .3; in the southern zone, less than .27.
The Cost of Replacement Windows Installation
Why is an understanding of Energy Star ratings necessary when looking for high performance windows? Because of the cost of installing replacement windows — it is important to find the best product possible for the specific needs of each individual home. According to Energy Star, buying replacement windows and paying for installation costs from $7,500 to $10,000. Knowing how to find the most energy efficient windows in the beginning will make installing replacement windows well worth the investment in the long run.
Sources:
- "Energy Performance Ratings for Windows, Doors, and Skylights." (US Department of Energy).
- " Windows, Doors, and Skylights." (Energy Star).
Brenna Coleman - Brenna is a freelance writer focusing on natural health and beauty. She has written hundreds of articles, helping readers find ways to ...
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