As an Alaska property owner, regardless of type, you will commonly hear mention of Home Energy Star Certification when discussing windows, doors, and skylights. Energy Star ratings can be very important to your bottom line when it comes to heating and cooling bills, so a clear understanding of the program and how the ratings are applied is essential.
What is an Energy Star rating?
Energy is a United States Environmental Protection Agency voluntary program that helps both businesses and individuals save money and protect the climate through the use of superior energy efficiency. The Energy Star program was first developed in 1992 by the United States Environmental Protection Agency (EPA) as a way of identifying and promoting products that are the most energy-efficient. Since its onset, the Energy Star program has expanded to cover a variety of products including, windows, doors, and major appliances.
A product that displays the Energy Star label is not necessarily “better” than a competing product; however, to receive the Energy Star qualification, a product must meet strict guidelines set forth by the program. As a property owner, you can use the energy performance ratings of windows, doors, and skylights to determine their potential for gaining and losing heat. You can also assess their potential for transmitting sunlight into your home, which can impact your heating and cooling bills. If you have old, metal or wooden windows that are not Energy Star certified, you may want to consider working with a home remodeling contractor such as Crighton Cooper Construction to switch your windows to Energy Star replacement windows.
Energy Performance Testing, Certification and Labeling
The National Fenestration Rating Council (NFRC) operates a voluntary program that is responsible for testing, certifying and labeling windows, doors, and skylights based on their energy performance ratings. For note, this is a voluntary program. This means manufacturers are not obligated to submit their products for testing or rating; however, being able to advertise a robust Energy Star rating can undoubtedly improve a product’s competitive ranking. Affixing the National Fenestration Rating Council label to a product provides a reliable way for consumers to determine the energy properties of a window. It provides a way to compare one window to another in terms of efficiency.
The National Fenestration Rating Council label can is found on all Energy Star qualified windows, doors, and skylight products. Still, Energy Star bases its qualification only on U-factor and heat gain coefficient ratings. These two rating groups are described in detail below.
Heat Gain and Loss
There are a variety of different ways windows, doors, and skylights can gain or lose heat. They include the following:
- Direct conduction- This form of heat transference occurs when heat enters or leaves the home directly through the glass or glazing, frame, and/or the door itself. This can also happen when the weather stripping or caulking placed around a window or door begin to wear away or break down.
- Radiation- Radiation of heat into the home (generally from the sun) and out of the house from room-temperature objects such as furniture, interior walls, and the people residing within the residence.
- Air leakage- Air can leak into or out of the home through the seals around windows, doors, or skylights. Also, in older windows or doors that have single-pane glass, you may experience air leakage.
These air transference properties can all be measured and rated according to various energy performance characteristics. They include U-factor, solar heat gain coefficient (SHGC), and air leakage.
The U-factor is the rate at which a window, door, or skylight conducts non-solar heat flow. For windows glass doors (solid glass or individual panels) and skylights, a U-factor assignment may just refer to just the glass or glazing itself. National Fenestration Rating Council U-factor ratings, on the other hand, represent the entire window performance, including the frame and any spacer material. The lower the U-factor, the more energy-efficient the window, door, or skylight is.
Solar heat gain coefficient (SHGC)
The solar heat gain coefficient is the fraction of solar radiation admitted through a window, door, or skylight. Solar radiation can be either transmitted directly or absorbed and subsequently released as heat inside the home. The lower the solar heat gain coefficient, the less solar heat is transmitted, and the higher the shading ability of the window, door, or skylight. A product with a high solar heat gain coefficient rating is more effective at reducing the cooling loads put on air conditioners and fans (leading to a smaller electric bill) during the summer by inhibiting heat gain resulting from the sun. Other factors, such as the climate, orientation, and external shading of your property, will also determine the optimal solar heat gain coefficient for a particular window, door, or skylight.
Air leakage ratings signify the rate of air movement around a window, door, or skylight in the presence of a specific pressure across the surface of the glass. This measurement is expressed in units of cubic feet per minute per square foot of frame area. A window, door, or skylight with a low air leakage rating is tighter than one with a high air leakage rating. It is also of value to note that the amount of air leakage can depend on several other factors, including the age of the window, the thickness of the glass, and whether or not the window was installed correctly. When ratings are derived for these products, proper installation is generally assumed.
Another factor used in determining how energy efficient a window, door, or skylight is sun transmittance. This rating describes the ability of glazing in a window, door, or skylight to transmit sunlight into a home. There are two characteristics used to measure and rate sunlight transmittance. They include visible transmittance and light to solar gain.
Visible transmittance (VT)
Visible transmittance is a fraction of the visible spectrum of sunlight weighted by the sensitivity of the human eye, that is transmitted through the glazing of a window, door or skylight. A product with a higher visible transmittance transmits more visible light. Visible transmittance is expressed as a number between zero and one. When you are selecting a window, door, or skylight for your property, you will determine the level of visible transmittance you need based on daylighting requirements and whether you need to reduce interior glare within the home.
Light-to-solar gain is the ratio between solar heat gain coefficient and visible transmittance. This number provides a way to gauge the relative efficiency of different glass or glazing types in transmitting daylight while blocking heat gains. The higher the light-to-solar gain ratio number, the more light transmitted without adding excessive amounts of heat. Unlike some of the numbers listed above, the ratio of light-to-solar gain is not always provided on the labeling of the window, door, or skylight you purchase.
To get the most benefit out of your Home Energy Star rated windows, doors, or skylights, they must be properly installed. Failure to properly install one of these products can make a highly rated product perform below expectations. If you are a homeowner or commercial property owner looking to update your windows or doors in the Anchorage, Alaska area look to Crighton & Cooper Construction. We will work with you to determine the proper products to install in your Alaska property.