Energy efficiency is a goal every home owner should keep in mind. Part of an overall energy efficiency effort are your windows. Choosing energy efficient windows may be a little costly at first. Over time you will recoup the cost of these windows and save yourself even more money as time goes on.
Not only is money an issue for energy efficiency. Pursuing an energy efficient home helps the environment. Reducing your home’s carbon footprint helps reduce greenhouse gas emissions. Generating electricity for home use is one of the main sources for human activity sources of dangerous greenhouse gasses.
Reasons to choose energy efficient windows
- Energy efficient windows can save an existing home up to 16% off of their annual heating costs. Installing energy efficient windows in a new home can save up to 26% off annual heating costs.
- Cooling costs can fall by as much as 43% for new construction and 37% for existing homes.
- HVAC loads are also often reduced with energy efficient windows. This brings an added benefit of lowering the cost of your HVAC unit for new constructions, or when purchasing a replacement system.
- An insulated window also helps keep your rooms more comfortable by providing a surface that more closely matches the interior temperature of your home.
- In cold climates you reduce the cold drafts from windows by having energy efficient options.
- Energy efficient windows no longer mean heavily tinted windows. New low-solar-gain low-E glazing allows you to see more clearly, while still allowing light into your rooms.
- Ultraviolet light fades many substances, energy efficient UV coatings have the added bonus of protecting your furnishings, carpets, and curtains.
- An added bonus to energy efficient windows is that they reduce exterior noise.
How Energy Efficient Windows Are Rated
- There are three characteristics that are rated by their energy performance characteristics.
- U-Factor: The rate that non-solar heat is conducted through a window. This may refer to just the glass, or the window as a whole. The lower this number is the less the window conducts heat.
- Solar Heat Gain Coefficient (SHGC): This rating measures the amount of solar radiation that is transmitted through, or released as heat inside of a room. The lower the SHGC number the less heat a window transmits and the better its ability to shade a room.
- Air Leakage: The ability of a window to restrict the movement of air through the window including frame. The lower this number the less air the window allows through it.
- There are two metrics that measure the transmittal of sunlight through a window.
- Visible Transmittance (VT): This is a measure of the visible light that a window allows through. This is a number between 0 and 1. The higher this number the more visible light that is allowed through a window.
- Light-to-Solar Gain (LSG): This is a number determined by the ratio between the SHGC and the VT. The higher the number the greater ability of the window to allow through light while blocking heat movement.
Energy Efficient Window Construction
There are many different ways that windows can be constructed. New methods are put into production all the time, and not every type of window can be described in our infographic. No matter the type of window there are three main elements. These elements are the Frame, the glazing, the fill, and the coating.
- Frame: The frame a window sits in needs to be as energy efficient as the glass itself. The material the glass sits inside of has to resist the transmission of heat. A windows U-Factor is impacted by the frame.
- Aluminum: Good for weight reasons, but easily transmits heat through the substance. This can sometimes be offset by using non-transmitting spacers to separate interior and exterior surfaces.
- Composite: Made of particle board or laminated lumber products. Composite frames have the benefits of wood, with a bit better ability to resist moisture and decay.
- Fiberglass: One of the best materials as it is structurally sound and may be constructed with air cavities that provide better insulation.
- Vinyl: Constructed of vinyl with stabilizers to resist ultraviolet let vinyl windows provide a bit more aesthetic value while still being superior to wood frames as they can be filled with insulation.
- Wood: Wood insulates well, but has issues with expansion, contraction and maintenance. Although one of the least expensive options, total cost for the lifespan of the window may be larger.
- Glazing: For energy efficient windows this means the type and number of pieces of glass that make up a window. The more panes of glass, the better energy efficient it will be. It also includes the space between these panes.
- Single Pane: One piece of glass without any gas fill, this is the least energy efficient.
- Double Paned: Two pieces of glass, separated by non-insulating spacers, may be filled with a gas that resists heat transfer. Most common type of energy efficient windows.
- Triple Paned: Similar to double paned glass, triple paned glass adds another piece of glass. This gives two gas filled spaces to further reduce heat transmission. It also helps reduce condensation.
- Gas Fill: Along with glazing is the gas that fills the space in windows. Using a gas fill reduces heat transmission from between the panes of glass. There are two types of gas usually used, both of them are safe, nontoxic, and odorless.
- Argon: Slightly cheaper than krypton argon is slightly less efficient at stopping heat transfer.
- Krypton: More expensive and also better at reducing heat transfer.
- Coating: The coating applied to window glass can make a large difference in the overall energy efficiency of the window. The ideal coating allows visible light through but stops heat from transferring through.
- Low-E: These coatings block specific wavelengths while not stopping visible light.
- Tinting: These coatings block a portion of visible and UV light.
- Reflective: These coatings reflect all but a fraction of visible light.