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How to Install Replacement Windows

Replacing single-pane windows with double-pane, low-e coated glass can make a house more energy efficient and save you money. Here's how to install a new unit.


  • Step 1: Remove the exterior trim Carefully remove the window frame's exterior trim using a flat pry bar and a hammer. Then, take out any exposed nails from the window frame.
  • Step 2: Expose the nailing fin With a tape measure and pencil, measure and mark a line 1 1/4 inch out from all sides of the existing window frame. Then, set a circular saw to the depth of the house's siding and cut along the line all the way around the window frame. Remove the cut piece with the pry bar to expose the window's nailing fin.
  • TIP: Take out any panels that open, known as active panels, from the old window before removal to make the unit lighter.
  • Step 3: Remove the old window Use a hand grinder to remove the heads from any nails in the nailing fin and pry the remaining window unit out from the wall. Pull out or drive down any remaining nails, and use the pry bar to clean out any caulking and debris from the empty window frame.
  • Step 4: Prepare the opening Measure from the replacement window's nailing fin to the interior edge. Add 1/8 inch to this length. Then, measuring from the outside in, mark and draw a line at this new value all the way around the inside of the window opening.
  • TIP: If the dry wall around the window frame is rotted, make additional adjustments to clear out the damaged area.
  • Step 5: Cut off the dry wall Cut completely through the dry wall along the line with a utility knife. Remove the cut strip of dry wall to allow for the replacement window's deeper setting.
  • Step 6: Install the new window Run a 1/4-inch bead of caulk around the opening, about 1/4 of an inch in from the exterior edge. Then, remove the active panels and screen from the replacement window and carefully set the new unit in the frame, pushing it into the caulking.
  • Step 7: Secure the window Hammer a 1 1/2-inch galvanized roofing nail into the frame's top-center nail hole to secure the replacement window. Then, reinstall the active panels, and close and latch the window to keep the window square.
  • Step 8: Add more nails Use a level to ensure the window is parallel to the ground; if not, shim the bottom of the window with scrap wood. Finish nailing in the window per the manufacturer's instructions.
  • Step 9: Cover the nailing fin Go outside. Using 6d galvanized box nails, install wood strips around the window. The strips should be 1/8 of an inch thinner than the siding that you removed from around the window to cover the nailing fin.
  • Step 10: Caulk the outside Caulk around the outside of the window. Spread and smooth the caulk with a putty knife, filling any voids around the wood strips to waterproof the siding beneath the trim. Then, reinstall the exterior trim, caulk the nail holes, touch up any exterior paint, and reinstall the screen.
  • Step 11: Finish up From inside, run a bead of caulk where the window frame meets the drywall, all the way around the new unit. Then, stand back and enjoy the view out of your energy-efficient, replacement windows.
  • FACT: According to the U.S. government, installing energy-efficient replacement windows can save a household as much $501 per year.

You Will Need

  • Flat pry bar
  • Hammer
  • Tape measure
  • Pencil
  • Circular saw
  • Hand grinder
  • Utility knife
  • Caulk
  • 1 1/2-in. galvanized roofing nails
  • Level
  • 6d galvanized box nails
  • Putty knife
  • Wood scraps (optional)

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