Understanding Your Fiberglass Window’s Energy Efficiency Performance

As a continuation from our last blog post, this article introduces the basic understanding of the energy efficiency performance of Energy Star qualified windows that have been tested by the NFRC. The National Fenestration Rating Council tests and rates Energy Star windows in order to help the consumer compare the most important ratings that impact the energy efficiency of your fiberglass windows and doors. The NFRC label can be found on Energy Star certified windows and doors and provides the five most crucial ratings that must be taken into consideration when choosing the most energy efficient fiberglass window for your home. The NFRC label can help you determine how well your fiberglass windows will perform during extreme climate changes such as heat, extreme cold, heavy winds and resistance to condensation.

U-Factor– The U-value measures the rate of heat transfer and tells you how well your fiberglass window or door insulates. U-values generally range from 0.25 to 1.25 and are measured in Btu/h•ft²•°F. The lower the U-factor, the better the window insulates. Fibertec’s fiberglass casement windows have a u-value as low as 0.13, which is extremely low and being a highly energy efficient fiberglass window.

Solar Heat Gain Co Efficient (SHGC) – SHGC can tell you how well your fiberglass windows can block out heat that comes from the sunlight. Measured from a scale of 0 to 1, the SHGC value usually ranges from 0.25 up, but not limited to 0.8. The lower the value of the SHGC, the less solar heat the window transmits. SHGC can be influenced by the type of glazing used, number of glass panes, and coatings that may be used such as hard or soft coatings. The frame material also has the ability to absorb radiation and can contribute to the overall rating of a window and energy efficiency.

Visible Transmittance (VT) – Visible transmittance is a value used to measure the amount of light the window lets through. VT is measured on a scale of 0 to 1 and generally ranges from 0.20 to 0.80. The higher the value of the VT, the more light enters through your windows. By adding a Low E coating, or tint to your glass, the value of visible light transmittance will decrease.

Air Leakage (AL) – The air leakage factor is the rate at which air passes through joints in the window. The air leakage value is measured in cubic feet of air that passes through one square foot of window area per minute. Is the AL value is low, you will experience less air leakage with your windows. The standard industry requirements and building codes demand an AL of 0.3 cf•m/ft². Sometimes people experience air infiltration with operable windows between the sash and frame if the window doesn’t have an air-tight seal. Using tight weather stripping is an important factor to consider when wanting to control air leakage and energy efficiency.

Condensation Resistance – Condensation can be a big problem when there is too much humidity, or if there is too much air leakage. The condensation resistance value will tell you how well your windows can withstand water build up. This factor is based on a scale of 0-100, where the higher the factor, the better your windows are and resisting water formation.

These five factors are crucial to understand when looking for the right fiberglass energy efficient windows for your home. These ratings can change for different fiberglass window styles over time, and thus it is important to look at the most updated ratings when looking for the right windows for your home.

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