How to Securely Close a Window After AC Removal

Quick answer (read this first)

• Thoroughly inspect and clean the window opening for debris or damage.
• Accurately measure the gap where the AC unit was to determine infill size.
• Cut and install appropriate infill material, such as plywood, to fit snugly.
• Seal all edges and gaps with caulk and add weather stripping for an airtight finish.

Safety first

• Always wear gloves and eye protection to prevent injury from tools or materials.
• Handle utility knives and other sharp tools with extreme caution.
• Use a sturdy step stool or ladder if working at height; never climb on unstable surfaces.
• Ensure all electrical connections related to the AC unit are fully disconnected and secured before starting.

Tools you may need

• Measuring tape
• Utility knife
• Screwdriver set
• Hammer
• Caulking gun
• Plywood or sturdy wood pieces
• Weather stripping
• Sealant or caulk
• Screws or nails

Step-by-step

Step 1

Prepare the Opening: Ensure the AC unit is completely removed and the window opening is cleared of all debris, old insulation, or loose screws. Clean the frame thoroughly.

Step 2

Inspect the Window Frame: Carefully examine the window frame for any signs of damage, rot, or warping. Address any minor issues now, as a sound frame is essential for a proper seal.

Step 3

Measure Accurately: Use a measuring tape to get precise height and width dimensions of the open gap, both from inside and outside. This ensures your infill material will fit snugly.

Step 4

Cut Infill Material: Based on your precise measurements, cut a piece of plywood or other sturdy wood. Double-check the fit for a tight, secure closure.

Step 5

Install and Secure Infill: Position the cut material firmly into the opening. Secure it in place using appropriate screws or nails, ensuring it is flush with the existing window frame.

Step 6

Apply Primary Sealant: Using a caulking gun, apply caulk or sealant generously around all edges of the installed infill and any remaining gaps. This creates a critical airtight and weatherproof barrier.

Step 7

Add Weather Stripping: For enhanced insulation and to prevent drafts, apply weather stripping along the edges of the newly installed infill or where the window sash meets the frame.

Step 8

Final Draft Check: After the sealant has cured (check product instructions), perform a draft test. Move your hand around the sealed area; if you feel air movement, apply additional sealant.

Common mistakes

• Not measuring accurately, leading to ill-fitting infill materials and recurring gaps.
• Using inadequate materials that don’t provide proper insulation or weather resistance, compromising efficiency.
• Forgetting to seal all edges, resulting in persistent drafts, moisture intrusion, and energy loss.
• Skipping the inspection of the window frame, which can lead to underlying issues resurfacing even after repair.
• Rushing the process and not ensuring a tight, secure fit for the infill material, causing instability and leaks.

When to call a professional

• If the window frame or surrounding wall shows severe structural damage, rot, or requires complex carpentry.
• If you encounter intricate issues with the window mechanism or sash that prevent proper closing, beyond simple sealing.
• If the opening is unusually large or requires custom fabrication and structural reinforcement beyond basic DIY skills.
• If you are unsure about selecting the right materials for weatherproofing or feel uncomfortable with the required tools and techniques.
• If drafts persist despite your best efforts, indicating a deeper issue that needs professional assessment and repair.