Don’t Take Window Installation Inspection Lightly! The Ultimate Checklist to Avoid Costly Mistakes

That moment after your new custom windows are installed might feel like a big relief. But wait—the real “final exam,” the inspection, is just beginning. Overlooking this crucial step can lead to all sorts of headaches down the road: water leaks, drafts, noise issues, and more.

As a professional custom door and window company, we’ve seen many cases of regret due to a rushed inspection. Today, we’ll be your personal “project supervisor,” guiding you step-by-step through this critical process to ensure you get exactly what you paid for.

A Cautionary Tale: Janerm’s “Window Regret”

After his renovation last year, Janerm was thrilled with how his new windows looked—sleek and modern. He signed the completion form without a thorough check. The first autumn storm revealed his mistake: water seeped in through a corner, and at night, the wind whistled through gaps. By then, it was a hassle to get repairs, and his new wallpaper was already damaged. This is a classic story of overlooking sealing and installation details.

Food for Thought: Are you worried that hidden flaws might become future annoyances? The following checklist is your tool to spot them.

The Ultimate 5-Step Window & Door Inspection Guide

We recommend following this “From Outside to Inside, From Static to Dynamic” sequence for a systematic check.

Step 1: The Visual “Doctor’s Visit” – Details Reveal True Quality

Before testing functionality, take a moment to inspect every detail like you’re examining a fine piece of art.

Part to Inspect	How to Check	Red Flags / “Failing” Signs
Glass Panes	Look closely against the light at the surface and interior.	Scratches, cracks, bubbles, or dust/moisture trapped inside.
3C Certification Mark	Gently scratch the mark with your fingernail.	The mark rubs off easily or is blurry (could be a counterfeit product).
Window Profile (Frame)	Run your hand over the surface, especially corners and edges.	Feeling burrs, dents, uneven paintwork, or color mismatches.
Hardware (Locks, Handles, Hinges)	Inspect closely for finish and integrity.	Visible rust, scratches, or screws on hinges that are loose or not fully driven.

Pro Tip: For double or triple-pane glass, the spacer bar (usually aluminum) is key. Opt for ones made with the “continuous bend“ technique instead of four-corner plug-in types. Continuous bend offers superior sealing, preventing dust and fog from entering the air gap.

Step 2: The “Ultimate” Seal Tests – Keeping the Elements Out

Looks good? Now for the main event—testing the seals. This is critical for preventing drafts and water leaks.

• The “Smoke Test” for Drafts: Light an incense stick or use a vape pen. Slowly move the smoke near closed window seams and where the frame meets the wall. If the smoke is clearly sucked out or wavers steadily, it indicates an air leak.
• The “Paper Test” for Compression: Close a sheet of A4 paper in the window. Lock the window. Now, try to pull the paper out. If it’s held firmly and you cannot remove it, the weatherstripping is creating a good seal.
• Inspect the Sealant Bead: Carefully examine the silicone sealant around the glass (where it meets the frame) and the frame (where it meets the wall). The bead should be continuous, smooth, evenly applied, and free of gaps, bubbles, or cracks. This reflects the installer’s skill.

Step 3: Function & Safety “Live Drill” – Smooth Operation is Key

Now, let’s get hands-on. Test the window’s operation and security.

1. Smooth Operation: Open and close the window at least ten times. It should feel smooth and easy, without grating noises or sticking.
2. Secure Locking: As you close and lock the window, ensure all locking points engage simultaneously. Try pushing firmly on the four corners of the closed window. A high-quality installation will feel solid with no movement. Significant movement suggests a security risk.
3. Drainage System: This is your first line of defense against water! Check the outside of the frame for drainage holes—there should be at least two. They should have covers to keep out insects and debris. The best test? Pour a glass of water into the window track and see if it drains away quickly and completely.

Step 4: Safety “Hardware Check” – Protecting Your Family

Q&A Time:
Q: The seller says the screen is “hardened stainless steel” (Diamond Mesh). How can I verify its strength?
A: Try gently scratching the mesh with a key (in an inconspicuous spot). Genuine, high-quality diamond mesh is very hard and should not show a clear scratch. If it does, it might be an inferior product.

• Glass Safety: Reconfirm that the 3C mark is permanent. For large panes of glass, this is a primary safety concern.
• Guardrail Safety: If you have young children and have floor-to-ceiling windows or low sills, protective bars are a must. Safety standards typically require vertical bar spacing less than 10cm (about 4 inches) and sufficient height.

Step 5: Paperwork “Final Audit” – The Contract is Your Guarantee

You’re almost done! Don’t forget to review the documents—this is your proof for any future claims.

• Verify Model Numbers: Take out your contract. Compare the window profile series, glass specifications (e.g., 5mm+20A+5mm), and hardware brand/models against what was agreed upon.
• Review Final Costs: Scrutinize the final invoice for any unauthorized “extra charges.” If certain agreed items weren’t installed, request a deduction immediately.
• Clarify Warranty: Confirm the warranty length and scope (does it cover just the product or also labor/installation?). Get a formal warranty card. For system windows, we recommend choosing a brand that offers a warranty of at least 5 years.

Conclusion: Your Master Inspection Checklist (Save or Print This!)

✅ Visuals: Glass, frame, and hardware are flawless. 3C mark is clear.
✅ Sealing: Smoke and paper tests passed. Sealant bead is perfect.
✅ Function: Operation is smooth, locking is secure, drainage works.
✅ Safety: Mesh is strong, glass has 3C, guardrails are compliant (if needed).
✅ Contract: Models, costs, and warranty match your agreement.

Your windows and doors are a vital barrier for your home. A meticulous inspection is an investment in your future comfort and peace of mind. We hope this detailed guide empowers you to confidently enjoy your new, comfortable home!

Do you have more questions about windows and doors? You can contact us, and our experts will be happy to help!