The NFRC label, which can be found on all ENERGY STAR qualified windows, provides performance ratings in a number of categories.
U-Factor: measures the rate of heat transfer & tells you how well the window insulates. The LOWER the U-Factor, the better the window insulates. The northern climate dictates a U-Factor of 0.35 or below. Unlimited’s Gold Series Double Hung has the lowest U-Factor of all 734 Energy Star window manufacturers with a 0.27 U-Factor.
Solar Heat Gain Coefficient (SHGC): measures the fraction of solar energy admitted and tells you how well the product blocks heat caused by sunlight. The lower the SHGC, the less solar heat the window transmits. SHGC is measured on a scale of 0 to 1; values typically range from 0.25 to 0.80. For the northern climate, any SGHC is allowed for the Energy Star criteria. Unlimited’s Gold Series Double Hung carries a .30 SHGC rating.
Visible Transmittance (VT): measures the amount of light the window lets through. The higher the VT, the more light you see. VT is measured on a scale of 0 to 1; values generally range from 0.20 to 0.80. Unlimited’s Gold Series Double Hung carries a 0.55 VT rating.
Condensation Resistance: measures how well the window resists water build-up. The higher the condensation resistance factor, the less build-up the window allows. Condensation Resistance is scored on a scale of 0 to 100. The Condensation Resistance rating is useful when comparing different products. Unlimited’s Gold Series Double Hung carries an outstanding Condensation Resistance rating of 63.