Great advice above. Couple small things -
- Make sure you're not in an historic district or have some other requirement (like a neighborhood covenant) that would make you get wood windows.
- If your house is worth a lot of money, don't get cheap windows. Personally, I would NEVER get wood windows again, why buy something that requires maintenance. YMMV !
Here's a big-ass articel from Consumer Reports, it's free here:
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Windows Upgrading to energy-efficient windows will likely improve your comfort and your home's aesthetics, but it will take years to recoup the initial outlay from energy savings
You'll probably want to install new replacement windows when you're remodeling, when the old ones have deteriorated, or when you want windows that are easier to wash and maintain.
Modern windows incorporate a frame made of all-vinyl or wood, the latter often covered in vinyl or aluminum, with two panes of glass.
To cut energy use, those panes are separated with air or another gas and sometimes specially coated. Improved comfort in the summer and winter is the major benefit, and slightly reduced heating or cooling costs will be an added bonus.
WHAT'S AVAILABLE
Window styles include double hung, sliding, hopper, awning, casement, and bay. The major brands are American Craftsman, Andersen, CertainTeed, Crestline, Marvin, Pella, Simonton (which also makes Sears models), and Weather Shield.
Some brands are sold at home centers such as Home Depot, Lowe's, and Menards. But most brands, including Sears, are typically purchased by contractors through distributors. Some windows come in custom sizes; others in stock sizes only. The materials that make a window frame can affect energy efficiency, maintenance, and price.
Price range: $150 to more than $400 for 3x5-foot, double-hung, double glazed windows.
Vinyl. These frames are easy to maintain, but they aren't usually available in many colors. And they are sometimes difficult to match with existing woodwork. Vinyl windows are often sold as a low-cost choice. Many were lower-performing models in our tests.
Aluminum. As vinyl frames have become more popular, aluminum frames have become less so. The biggest drawback is that they allow heat to escape. That can make the area around the window chilly. In places with cold winters, a simple aluminum frame can become cold enough to condense moisture or frost on the inside, but where winters are mild, aluminum can be a good choice for its durability. If you are set on buying aluminum-framed windows, choose ones that have "thermally broken" frames, with insulating material between interior and exterior components.
Wood. For elegance, wood is difficult to beat, although it usually costs more than vinyl and requires painting or staining and other maintenance. To minimize maintenance where it's usually needed most--the exterior side--many manufacturers cover, or clad, the wood in vinyl or aluminum. Wood composite frames--some made from a mixture of wood fibers and plastic resins--are supposed to combine the durability of wood with the low upkeep of plastics.
Important features
Three types of glazing are commonly available: single, double, and triple. A single pane of glass, or single-glazed, allows the highest transfer of energy and offers little insulation against frigid winters and searing summers. Double-glazed windows have two panes of glass. A few manufacturers offer triple glazing.
The gas between the glass has a bearing on the quality of insulation. Plain old air works fine and is standard for some brand lines. Argon gas, which provides better thermal performance, is standard in other brand lines; sometimes it is a step-up option. A few top-of-the-line windows incorporate krypton gas, which provides incrementally better insulation.
Double- and triple-glazed windows are sealed assemblies so they retain any special gas between the panes and also keep out moisture, which can condense between the panes. Should the seal fail, moisture, water droplets, and fogging between the glass panes can occur.
Clear glass lets a relatively large amount of radiant energy (heat in from the sun during the summer, heat out from your home during the winter) to pass through. Low-E coatings (the "E" stands for emissivity, or the ability of a surface to emit heat) enhance the insulation quality of a window by making it reflect heat.
These coatings reduce some of the visible light that passes through the glass and may give a tinted appearance. The view out at night may be impeded somewhat. The coatings can be fine-tuned for different climates--a southern or a northern window, for example.
Most new double-hung windows have tilting sashes, a very handy feature that lets you pivot them inward for easier cleaning. With most, you simply flip a lever or two to tilt the sash inward. But with some, you must pull the sash out of the track.
Mullions are decorative vertical elements that separate panes of glass. To help keep out water, some windows have a thin lip-a strip of wood or vinyl about an inch high-that rises from the sill. You'll need to work around it when installing a room air conditioner.
How to choose
Performance differences. Consumer Reports has found most windows do a very good or excellent job at sealing out a fairly strong wind when the outside thermometer registers 70=B0 F. Only a handful do well at sealing out a high wind when the outside temperature drops to zero. When it's that cold, weather stripping and other components can stiffen or shrink. Our tests have shown that aluminum frames are durable. But we have found windows with frames made of vinyl- or aluminum-clad wood can perform well, too.
Recommendations. If you're replacing windows, choose those that are designed for your region's climate. Cooling costs predominate in southern regions, so look for double glazing and a low-E coating. Give first consideration to windows with a low solar-heat-gain coefficient. The Department of Energy recommends that the number be 0.4 or lower.
Heating bills are of concern in northern regions. Give priority to well-insulated, double-glazed windows that are draft-free. A low-E coating isn't essential in places where summers aren't particularly hot. In central regions, both heating and cooling are concerns. As in southern regions, look for double glazing and a low-E coating. You'll also want high insulating performance and a solar-heat-gain coefficient of 0.55 or lower.