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Buy Energy Efficient Windows

If your windows are in good condition, taking steps to improve their efficiency may be the most cost-effective option to increase the comfort of your home and save money on energy costs. There are several things you can do to improve the efficiency of your existing windows:

buy energy efficient windows

First look for the ENERGY STAR label when buying new windows. Then review ratings on the energy performance label from the National Fenestration Rating Council (NFRC) to find the most efficient windows for your needs.

The energy savings of fenestration products varies according to climate. When choosing fenestration products, first identify the climate zone where they will be installed and then find products with U-factors and solar heat gain coefficients (SHGCs) that are less than or equal to those specified by ENERGY STAR.

The Federal Energy Management Program (FEMP) provides acquisition guidance for residential windows, doors, and skylights, a product category covered by ENERGY STAR efficiency requirements. Federal laws and requirements mandate that agencies purchase ENERGY STAR-qualified products or FEMP-designated products in all product categories covered by these programs and in any acquisition actions that are not specifically exempted by law.

FEMP's acquisition guidance and associated ENERGY STAR efficiency requirements for residential windows, doors, and skylights are technology neutral, meaning that one technology is not favored over another. However, ENERGY STAR's product specification requirements are limited to products that meet the definition of a residential window, door, or skylight as specified in the product specification information.

All other residential windows, doors, and skylights types are excluded, including but not limited to products that are assembled on site, sash packs or sash kits; windows, doors, or skylights that are intended for installation in nonresidential buildings; and window, door, or skylight attachments that are not included in a product's National Fenestration Rating Council (NFRC)-certified rating.

The U.S. Environmental Protection Agency (EPA) provides residential window, door, and skylight efficiency levels and product specification information on its ENERGY STAR website. Manufacturers meeting these requirements are allowed to display the ENERGY STAR label on complying models. Get a list of ENERGY STAR-certified residential windows, doors, and skylights by climate zone in the NFRC's directory search.

Fenestration products, such as windows, doors, and skylights, do not consume energy directly. They do, however, add to the heating and cooling loads of the buildings in which they are installed. Selecting and installing energy-efficient windows, doors, and skylights can minimize these additional space conditioning loads and reduce the amount of energy used by the building's heating and cooling system.

Unlike many products, the energy savings of fenestration products varies according to climate. Features that make windows energy efficient in one type of climate may offer little benefit in another. The energy efficiency of fenestration products is primarily a function of the U-factor (thermal transmittance) and solar heat gain coefficient (SHGC). When choosing fenestration products, first identify the climate zone where they will be installed and then find products with U-factors and SHGCs that are less than or equal to those specified by ENERGY STAR.

FEMP has calculated that the required ENERGY STAR-qualified residential windows, doors, and skylights save money if priced no more than $2/ft2 (in 2020 dollars) above less efficient models. The best available models save up to $4/ft2. Table 1 compares three types of product purchases and calculates the lifetime cost savings of purchasing efficient models. The results in the table are based on windows, which represent the largest market segment. Federal purchasers can assume products that meet ENERGY STAR efficiency requirements are life cycle cost-effective.

Annual Energy Cost: Calculated based on an assumed electricity price of $0.09/kWh, which is the average electricity price at federal facilities, and the heating load energy cost is calculated based on an assumed natural gas price of $0.63/therm, which is the average natural gas price at federal facilities. Learn more about Federal Government Energy/Water Use and Emissions.

Calculated for triple-pane, low-emissivity, low visible transmittance, argon windows with a U-value of 0.12 and a solar heat gain coefficient (SHGC) of 0.21, from the Regents of the University of Minnesota, Center for Sustainable Building Research Design Guidance for Offices in Minneapolis, Minnesota. More efficient models may be introduced to the market after FEMP's acquisition guidance is posted.

An efficient product is cost-effective when the lifetime energy savings (from avoided energy costs over the life of the product, discounted to present value) exceed the additional up-front cost (if any) compared to a less efficient option. ENERGY STAR considers up-front costs and lifetime energy savings when setting required efficiency levels. Federal purchasers can assume ENERGY STAR-qualified products and products that meet FEMP-designated efficiency requirements are life cycle cost-effective. In high-use applications or when energy rates are above the federal average, purchasers may save more if they specify products that exceed federal efficiency requirements (e.g., the best available model).

Products meeting ENERGY STAR or FEMP-designated efficiency requirements may not be life cycle cost-effective in certain low-use applications or in locations with very low rates for electricity or natural gas. However, for most applications, purchasers will find that energy-efficient products have the lowest life cycle cost.

These mandatory requirements apply to all forms of procurement, including construction guide and project specifications; renovation, repair, energy service, and operation and maintenance (O&M) contracts; lease agreements; acquisitions made using purchase cards; and solicitations for offers. Federal Acquisition Regulation (FAR) Part 23.206 requires agencies to insert the clause at FAR section 52.223-15 into contracts and solicitations that deliver, acquire, furnish, or specify energy-consuming products for use in federal government facilities. To comply with FAR requirements, FEMP recommends that agencies incorporate efficiency requirements into technical specifications, the evaluation criteria of solicitations, and the evaluations of solicitation responses.

The federal supply sources for energy-efficient products are the General Services Administration (GSA) and the Defense Logistics Agency (DLA). GSA sells products through its Multiple Awards Schedules program and online shopping network, GSA Advantage!. DLA offers products through the Defense Supply Center Philadelphia and online through FedMall (formerly DOD EMALL). Products sold through DLA are codified with a 13-digit National Stock Number (NSN) and, in some cases, a two-letter Environmental Attribute Code (ENAC). The ENAC identifies items that have positive environmental characteristics and meet standards set by an approved third party, such as FEMP and ENERGY STAR.

Not all windows sold by GSA are ENERGY STAR-qualified, and some products that do qualify may not be indicated as such. When buying windows from this source, check models against the ENERGY STAR website or the NFRC Certified Products Directory.

The heat lost or gained through fenestration can have a substantial impact on the energy required to condition a building. Heat transfer through fenestration is a function of the difference between indoor and outdoor temperatures and the U-factor of the glazing system. The U-factor is a measure of the rate of heat flow through glazing products; the lower a U-factor, the less heat will flow through the window. In the United States, U-factors are reported in Btu/(hft2F), and typically range between 0.2 to 1.2 Btu/(hft2F).

Visible transmittance (VT) is a measure of the amount of energy within the visible spectrum (light) that passes through a glazing unit. Although similar to SHGC, VT indicates how much daylight is transmitted whereas SHGC is a measurement of the amount of heat transmitted. The NFRC Certified Products Directory and NFRC labels typically report VT, which is expressed as a value from 0 to 1. The VT of actual fenestration products, which includes opaque areas such as the frame and sash, varies between 0.10 and 0.80. A higher value indicates that a greater percentage of light is transmitted through the window. Typically, high values are preferred in residential applications. VT values below 0.5 noticeably reduce the amount of light transmitted. When purchasing windows with a low SHGC, verify that the VT is not too low.

Although an air leakage rating is not required by ENERGY STAR, air leakage through fenestration can be a significant source of heat loss or gain in a building. The air infiltration of many fenestration products is reported in the NFRC Certified Products Directory and on NFRC labels. The air leakage rate is a measure of how much air leaks through cracks in a window under reestablished test temperatures and pressure differences. Although the air leakage is reported in cubic feet per minute per window area in the NFRC Certified Products Directory (cfm/ft2), some manufacturers report air infiltration in cubic feet per minute per linear foot of window edge (cfm/ft). A lower value means less air leakage. Minimizing the air infiltration through windows increases occupant comfort by reducing drafts and condensation.

In warm climates, where air conditioning costs are the concern, buy or specify products with low SHGCs to reduce unwanted heat gain. Windows with low-e coatings, especially spectrally selective coatings, are effective at reducing summer heat gain and air conditioning costs without significantly impacting visible light or color. Tinted windows also reduce solar heat gain but transmit less visible light and, therefore, often have an undesirable aesthetic impact. Although windows and skylights are often designed to be operable (i.e., open to allow air to pass), it is desirable to choose windows with low air leakage rates, especially if the building is air conditioned. 041b061a72


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