Measuring and Ordering

• Don't take out your old windows until your new ones are on site. To order your new windows, you'll need to provide the width and height of the opening. To get the number, measure the width of the opening at three different spots along the jamb. Take the smallest reading and subtract 1/4 inch from it. (so if your three width measurements are 31 inches, 30-3/4 inches and 30-1/2 inches, your ordering width should be 30-1/4 inches). Do the same for the height number. Make sure you're measuring all the way to the window jamb, which is the flat span of wood that the window presses against on all sides.
  
  

Rip-out

• To remove the old windows, use a hammer and pry bar to carefully remove the thin vertical trim that holds in the bottom sash. Try not to damage the trim, as you'll need to put it back in. Remove the bottom sash, cutting the cord to the window weights if necessary. (You can let the weights fall into the wall.) Remove the vertical divider strip in front of the top sash, and take the top sash out. Leave the exterior framing in place.
  
  

Installation

• Set the new window on the bottom plate of the opening, and push the top in. The exterior trim will prevent it from falling out the other side. Shim the sides and bottom until the unit is level and plumb in the opening, checking it in all directions with a level. Use long wood screws to mount the window to the side jambs. (There will be screw holes on the sides of the unit.) Stuff loose insulation into the cracks around the sides, bottom and top of the window--anywhere you can get it in. Put the vertical trim back on, so it covers the space between the window unit and the opening. Caulk between the window and the trim.