Create a mini-sunroom with a bay window
This bay window includes double-hung windows on each side. Notice the decorative grille that lines up with the double-hung sash line.
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 (and gain, in summer) through the glass itself, but there likely is no insulation around it inside the walls. If one faces south or west, count on the drapes, furniture and carpeting near it to be badly faded.
A bow or bay window, sometimes called the "poor man's sunroom," can be an attractive replacement. A bow or bay window can provide some of the benefits of a sunroom at a lower cost. These include making your room appear larger, providing a seat at the window, and creating an ideal location for plants. Even though it costs considerably less than adding a small sunroom, installing an efficient bow or bay window is still not an inexpensive home-improvement project.
No matter what type of new window design you install, it will be more efficient than an old picture window and reduce your utility bills. This savings can help to pay back its initial cost, but it will take many years to pay back the entire cost. By including the utility bills savings with the increase in your home's resale value, you should be able to recover most of the cost over a reasonable time period.
The basic difference between a bow and a bay window is 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. 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. It creates more of a mini-sunroom feel.
There is not a significant difference in the energy efficiency or durability of a bow or bay window. A bay window may be slightly more efficient because there are fewer joints and seams to be sealed. Also, wherever there is framing material and supporting lumber in the wall, there is less room for insulation.
Select the most energy-efficient glass your budget will allow. At the very minimum, select double-pane glass with a low-emissivity coating and inert gas in the gap between the panes. Make sure to select the proper glass for your area because the location of the low-emissivity coating can vary depending upon your climate. All the new glass types will reduce fading.
Because a bow or bay window protrudes from the wall, it is ideal for natural ventilation during summer to reduce your air-conditioning costs. 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.