This tall wood bow window with equal-width casement sections, left, offers a curved appearance. A bay window has two narrow angled side windows and a wider center window.
Question: I have an old picture window I want to replace with a bay or bow window. Which type is best and most efficient? Should I buy an entire unit or assemble one from individual windows?
Answer: Those old, large, single-pane picture windows, which were common in houses built many years ago, are extremely inefficient. Not only is there a huge heat loss in winter (and gain, in summer) through the glass itself, but there likely is no insulation around it inside the walls.
A bow or bay window, sometimes called a “poor man’s sunroom,” is a good replacement option. Either style will make your room appear larger, provide a seat under glass at the window and create an ideal location for plants. They are also more efficient and will help reduce your utility bills—at least a little bit. These savings can help offset the cost of new windows, but it will take many years to pay back the entire cost.
What’s the difference between a bow and a bay window? A bow window is made of four or more narrow window panels, often of the same width. Five windows is the most common configuration. Using more window panels creates a more circular appearance, which many people find attractive. Often, only the two end windows can be opened, but you can order them so they all open.
Bay windows are made from just three window panels. The two angled side panels usually can be opened and are angled at either 30 or 45 degrees. The fixed center window is similar to a smaller picture window with an unobstructed view of the outdoors. A 45-degree bay window extends further than a 30-degree window from the house wall and provides more space for plants or a bench seat.
There is no significant difference in the energy efficiency or durability between a bow or bay window. As with any replacement window, the glass is an important detail to consider. Select the most energy-efficient glass your budget will allow, even if it forces you to cut back on the styling or trim options. At the very minimum, select double-pane glass with a lowemissivity coating and inert gas in the gap between the panes.
In addition to high-quality glass, look for a bow or bay window that has insulation, often foam, in the seatboard and the top. This saves energy and improves your comfort near the window. Your plants will also appreciate it during winter.
Unless you are very handy with tools, it is generally better to purchase an entire unit designed as a bow or bay window. This will cost a little more than assembling one from individual windows, but it will likely be stronger and more airtight. Some models use quite sophisticated designs to support the bow or bay window because it is cantilevered out from the wall.
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The following companies offer bow and bay windows:
Champion Window, (800) 875-5575.
Thermal Industries, (800) 245-1540.
Weathershield Windows, (800) 222-2995.