How to Replace a Thermal Pane Window

Thermal pane windows have extra layers of glass in them, to better insulate the home against the elements. The air between the layers serves as the insulation. Replacing those windows is the same process as replacing standard single-pane windows, as most replacement windows today come prehung in self-contained units. You don't have to replace thermal pane windows with similarly energy-efficient windows, but if you don't, you'll be going backward in terms of energy savings.

Tape measure
Pry bar
Hammer
Level
Wood shims
Screw gun
Mounting screws (provided with new window unit)
Fiberglass insulation
Finishing nails
Caulk
Caulk gun

Instructions

- 1
  Measure the dimensions of the window opening while the existing windows are still in place, along the height and width, in the tracks where the sashes sit. These are the proper measurements for the replacement window unit. Leave the old window in place until you have the new ones in hand.
- 2
  Remove the trim from the interior edge of the window opening, using your hammer and pry bar. Don't break the trim as you remove it. Pull out the sashes.
- 3
  Set the new window unit on the bottom span of the opening. Push the top up and in, until it's stopped by the trim around the outside of the opening. Hold your level on the unit and shim around it until it's level and square.
- 4
  Secure the unit with mounting screws, shooting them outward through the screw holes in the sides with your screw gun, and into the wall frame along the edges of the opening.
- 5
  Tuck fiberglass insulation into the spaces around the edges of the window unit on all sides, closing off the spaces.
- 6
  Put the trim back in, using your hammer and finishing nails.
- 7
  Caulk around the trim where it meets the wall and the window unit, using a caulk gun.

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