You’ve probably heard by now that installing energy efficient windows can help to reduce the cost of your monthly energy bill by sealing in heat when it’s cold and cool air when it’s hot outside.
While that’s definitely true, and replacing single pane windows with energy efficient windows could easily save you $500 each year, there is another a great benefit.
Energy efficient windows are good for the environment because their installation helps to reduce greenhouse gas emissions.
They’ll also make your home more comfortable for you and your family because you won’t be dealing with constant temperature fluctuations like you do with single pane windows.
Even for homeowners that are already doing their part to conserve energy, energy efficient windows are a smart decision for your bottom line and for the environment.
So how can your windows make your home more energy efficient?
That conundrum bothered the brains of physicists until sometime in the 19th century.
Building on the theories of Francis Bacon, physicists realized that heat was thermal energy, was billions of atoms bouncing around like marbles in a clothes dryer, and that it actually worked in three different ways:
- Conduction: You touch a hot pan. You burn.
- Convection: An autumn wind – considered a “fluid” in thermodynamics – cools your skin.
- Radiation: You forget to apply SPF 50 sunscreen while swimming. Again, you burn.
How Do Traditional Windows Work?
To you, a window is a prescription for cabin fever. To thermodynamics, a window, and other types of fenestration, is a chink in the armor of your home.
Your house is built to modulate the flow of heat, to preserve it in winter and banish it in summer. A window allows heat to act as it pleases.
Traditional windows are very easy to understand. They’re usually hinged encasements with one pane or two panes of glass, and that’s pretty much it. Energy efficient windows are much more technically advanced.
Standard windows are commonly made from clear glass.
Cracks in the caulking of your windows allow heat to leak via convective drafts.
Solar radiation transforms bedrooms into ovens. In the winter, warmth in the air escapes by passing through thin glass into the Great and Snowy Outdoors.
Windows Can Make Your Home Energy Inefficient
All of these problems beset single-pane windows, which were once standard fare throughout all of America.
Although affordable, single-pane windows transmit heat and noise without putting up a fight.
One study estimates that a single-pane window allows 10 times as much heat to escape compared to the same area of insulated wall.
Another reports that 15-22% of a home’s heat escapes through the windows.
Such costs escalate into the hundreds of dollars per year, every year, without fail. Surely, there is some way to stop the flow of heat and cash?
How Do Energy Efficient Windows Work?
Energy efficient windows incorporate various types of different glazes to keep the weather outside from getting into your home.
Common glazing options for energy efficient windows include double clear, double tint and low-emittance coatings. Some manufacturers also employ different types of solar resistant film within the casing to reduce heat transfer.
Beating Conduction Heat Loss with Multi-Pane Windows
Standard windows – even windows that employ two panes of glass – are just that: pieces of glass with nothing between them.
A two-pane window is more energy efficient than a single pane window, but it can’t really be called an energy efficient window.
Welcome to double-pane windows.
Built like a sandwich, with a pad of gas between two glass sheets, double-pane windows can save you 20-30% on annual energy costs.
Most double-pane windows use air for the inner gas. Some use argon gas for its greater insulation power, a property measured in “R-value.” When placed between two panes of a window, argon helps to improve the thermal performance of a piece of glass.
Top-tier manufacturers sell exorbitantly expensive triple-pane windows filled with krypton.
Multi-pane windows help prevent heat loss through conduction. Keep in mind, however, that not all double-pane windows are created equal. Your frame is important, too.
Cheap model frames are built from aluminum, a metal that conducts heat like a river conducts water.
A better framing option is vinyl, or higher quality materials (more on that in a minute).
Beating Radiation Heat Loss with Window Coverings and Coatings
Drapes, curtains or blinds help solve another problem: radiation.
When sunlight hits your glass window, some bounces off, some heats up the glass, and some passes into your home, where it fades furniture, warms the air and delights your cat.
Covering your windows with heavy drapes or curtains will further boost the R-value of your windows.
In hot, arid climates like Arizona, some homeowners fend off solar radiation by installing window awnings or overhangs, which are often made from metal or canvas.
Throughout the rest of the nation, homeowners use low-emissivity (low-E) window coatings.
These translucent coatings, thinner than a human air, reduce the heat re-emitted by warm windows, are usually applied to south-facing windows.
Other window coatings include reflective glazes, spectrally selective coatings and dark tints.
Beating Convection Heat Loss with Weather-stripping and Window Styles
How your windows are hung may help or hinder heat loss through convection, that is, air drafts.
Fixed windows, the ones that don’t open, are usually airtight. Other energy-efficient styles include awning, casement and hopper windows.
The most popular window styles, which are single- and double-hung and single- and double-sliding, rank at the bottom.
Traditionally, window frames are made of wood, and while wood window frames are built to and normally last for years, they don’t do much for energy efficiency within a home.
That’s why many manufacturers of energy efficient windows suggest using metal window frames with a thermal break or non-metal frames with thermal enhancements.
Without getting too technical, metal window frames with a thermal break split the frame into interior and exterior components and use a less conductive material to join them, reducing heat transfer.
Non-metal frames are typically made with composite materials or materials like fiberglass designed to look like wood that reduce the amount of dead space in the frame itself, helping to reduce overall heat transfer as a result.
How Helpful Are Energy Efficient Windows?
Energy efficient windows are a great way to reduce overall heating and cooling costs in your home and you’ll get back the money you spend in savings in a couple years’ time.
However, installing energy efficient windows can also help you do your part to keep the environment clean and green.
Older buildings and single-family homes alike can benefit from the environmental benefits and cost-savings offered by energy efficient windows.
If you already take steps to keep the earth green, installing energy efficient windows just makes sense.
Purchasing energy-efficient windows, like ENERGY STAR-certified double-pane windows, can save you hundreds of dollars in annual energy costs.
Recommended window designs and coatings vary by region, so talk with a local professional before spending $10,000 on retrofitting.
Editor’s Note: This post has been updated for freshness and consistency.