Which replacement window saves you the most money?

You may be hearing a lot these days about "inefficient" windows. That word is used as a catch-all to describe windows that are old, leaking, and/or not helping you save money on your heating and cooling costs. If you've decided to make the switch over to "efficient" windows, you'll encounter a whole slew of questions over everything from glass types (do you need low-e? Triple glazed?) to window material (is a vinyl, wood, or metal window best for your area?).

With so many options, it can be difficult to make an informed decision that's actually going to save you money instead of wasting it on upgrades that may be unnecessary for your climate.

Luckily, the Efficient Windows Collaborative is available online to help. This non-biased site requires some basic information about your geographic location, the direction your home faces, the amount of sunlight you get, how much window area you have, and how much of your window area is shaded. With this in hand, it helps you figure out the exact window you need.

Let's use an example home in Nashville, TN to guide us through why all this information matters.

1. Location: Your location determines which Energy Zone your home lies in. The four Energy Star zones established by the Department of Energy determine the rating of glass needed to meet required u-values (resistance to heat flow - the lower the value the less heat moves through that material) and Solar Heat Gain Coefficient (also called SHGC, this is the amount of the sun's energy that passes through the material). Homes in hotter areas would want less heat and light to pass through the windows while homes in colder areas would want more. Our home in Nashville is in the North/Central zone.
2. Orientation: This is the direction your home faces - north, east, south, or west. Let's say our house in Nashville faces west as do most of its windows. A high amount of sunlight enters the home year-round.
3. Window Area: The percentage of glass per wall helps determine how much surface area heat or cold has to come into your home. You can simply select small, medium, or large to make it easy to estimate. Our Nashville house has a large window area - over 20%.
4. Shading: Does your home get direct sunlight, is it fully shaded, or is there a mix? We'll say the house is Nashville gets direct sunlight.

Once all this information has been entered, your various window variables will be displayed: how many panes of glass you can have (also called glazing - so three panes of glass would be a triple glazed window), what kind of glass you can have (low-e, tinted, etc.), and your frame options (metal or non-metal). Next to each option, you'll find real information about the total heating and cooling costs you can expect to pay over the course of a year with that window. Here are the Nashville window options with their associated costs.

With this information in mind, you can start window shopping with an informed idea about the glass and window type best for your home. You can save money in the short term by not going for an upgrade you don't really need, and you can look forward to long-term heating and cooling savings with your efficient, just-right windows.