Kits

• A window sash consists of the window pane and the frame surrounding it. For most jobs, you can get a window sash replacement kit from a home improvement store. These kits are made by large, well-known window makers such as Pella, Marvin and Anderson. Look for a kit that comes with everything you'll need for a complete replacement, including lower and upper sash, parting stop, jamb liners, sash lock and brackets. Using a kit, you'll be able to replace the sash while retaining the window frame and the interior and exterior trim, leaving the look of your home intact.
  
  

Types

• Wooden window sashes are the most common type, but they tend to crack or warp over time. This is the sash type you're most likely to encounter in older homes. Newer homes may feature aluminum and vinyl sashes that don't have the cracking or warping problems of wood and also are lighter and stronger. Most kits will come with the newer materials, but wood sash kits are available if you prefer this traditional style.
  
  

Replacement

• Measure your window carefully before ordering the replacement kit. Many kits are made to fit standard-sized windows, but if the sash you're replacing is for an older home or for an irregularly sized window, you can order a custom sash that will fit the opening like a glove. An exact measurement is critical, as any sizing mistakes likely will result in worse energy loss than before. Some window dealers will send someone to your home to make the measurements.
  
  Many older windows have a rope and cast-iron weight for opening and closing. You can find replacements that use the same system, but most kits instead opt for a spring-loaded jamb system that's a bit more energy-efficient. If you decide to replace the rope and weight, fill in the space with expanding foam insulation to cut off energy leakage. The insulation also helps cut down on noise pollution from outside the home.
  
  Doing the replacement yourself will save you some money. In 2009, a carpenter's charge for a 30-inch-by-54-inch window was about $415; you could do the same job yourself for about $325. Expect each window to take you about four hours to complete.