Replacing the sash on an Andersen double hung window is often the most cost-effective way to restore function and improve energy efficiency without a full frame replacement. Over time, the original sash can warp, rot, or develop failed glazing, leading to air leaks and difficulty operating the window. This guide provides a detailed, step-by-step process for removing the old unit and installing a new one, focusing on the specific mechanics of the Andersen design.
Understanding Your Andersen Double Hung Components
Before beginning the removal, familiarize yourself with how the window is constructed. An Andersen double hung typically features two vertically sliding sashes held together by a split rail design. The window is secured within the surrounding frame using clips or brackets that grip the jambs. The primary challenge in replacement is accessing these mounting points without damaging the surrounding trim or wall surface.
Tools and Materials Required
Safety goggles and work gloves
Putty knife or chisel set
Flathead and Phillips screwdrivers
Reciprocating saw with wood blade (optional)
Caulking gun and exterior-grade caulk
Replacement sash specific to your model number
Wood shims for alignment
Removing the Interior Sash
Start by moving the lower sash to the fully raised position and securing it in place. This grants clear access to the upper sash operation. Locate the tilt mechanism on the side of the window; this is usually a metal bar or pin. Rotate the tilt latch to the "unlock" position, which allows the upper sash to tilt inward for removal.
Detaching the Sash
With the tilt mechanism unlocked, lift the upper sash slightly to clear the tracks. Carefully angle the sash inward and then lift it vertically out of the window frame. Set the removed sash on a stable surface, ensuring the glass, if present, is facing down to avoid pressure on the panes. Repeat the process for the lower sash if it also requires replacement.
Measuring and Ordering the Replacement
Do not assume the new sash will fit based on the dimensions of the frame opening. Instead, measure the channel or jamb where the sash slides. Measure the height from the bottom rail to the top of the channel and the width at the top and bottom of the channel. These are the dimensions required for a perfect fit. Contact Andersen customer service or your retailer with these measurements to confirm the correct part number before purchasing.
Installing the New Sash
With the new sash ready, position it into the window channel from the side. Align the mounting holes on the new sash with the clips inside the frame. Gently press the sash into place, applying even pressure to engage the clips with the mounting slots. You should hear or feel a distinct "click" as the clips lock the sash into position, preventing it from lifting out vertically.
Securing and Testing
Once both sashes are seated, test the vertical slide operation. The sashes should move smoothly without binding or excessive resistance. If the movement is stiff, check for paint rub between the sash and the channel; lightly sand any contact points. Ensure the split rail locks together correctly when the window is closed, creating a tight seal to prevent air infiltration.
Finishing the Installation
After confirming the mechanics work correctly, address the exterior appearance. If the new sash came with pre-finished trim, ensure it aligns with the existing window casing. Use wood shims between the sash jamb and the rough opening to align the unit perfectly plumb and level. Once aligned, secure the perimeter with additional nails or screws, taking care not to overtighten and warp the frame.
