Windows

How to Insulate Old Windows for Better Comfort and Energy Savings

If you’re trying to figure out how to insulate old windows, you’re not alone. Many homeowners love the charm and character of their original windows—but not the drafts, noise, or high heating bills that often come with them. Fortunately, there are several effective, budget-friendly ways to insulate older windows and make your home more energy-efficient without replacing them entirely.

Want expert advice or materials for your next window project? Call 866-739-1636 or contact Builders Surplus to get started with affordable solutions for your home.

Why Insulate Old Windows?

Insulating old windows helps with more than just comfort. It also reduces energy costs, prevents moisture problems, and increases your home’s value.

Top benefits of window insulation:

• Lower utility bills – Less warm air escapes in winter, and cool air stays in during summer.
• Improved comfort – Say goodbye to cold drafts and chilly corners.
• Noise reduction – Insulated windows help buffer street and neighborhood noise.
• Condensation control – Reduces the chance of moisture buildup that can lead to mold or damage.
  

While window replacement may be ideal in the long term, short-term solutions can provide big benefits for a small investment.

Step-by-Step: How to Insulate Old Windows

Let’s walk through the most effective ways to insulate your windows, from quick fixes to longer-term solutions.

1. Use Weatherstripping Around Window Frames

Weatherstripping is one of the fastest, easiest, and most affordable ways to seal gaps where warm air leaks out. It’s especially helpful on windows that still open and close.

Types of weatherstripping include:

• Adhesive-backed foam tape – Ideal for window sashes and frames
• V-seal (V-strip) – A durable plastic or metal strip for sliding windows
• Felt or rubber strips – Easy to cut and apply in gaps
  

Tip: Clean surfaces before application to ensure good adhesion. Reapply annually if needed.

2. Apply Window Insulation Film

Window insulation kits are available at most home improvement stores and are a go-to solution in colder climates. These kits include a clear plastic film that you apply to the interior of the window frame and shrink tight with a hairdryer.

Why it works:

• Creates an invisible barrier against cold air
• Reduces frost buildup and condensation
• Can be removed in spring without damage
  

This is a great seasonal fix, especially for drafty windows in bedrooms or living areas.

3. Caulk Cracks and Gaps

Older windows often have tiny gaps where the frame meets the wall or glass. Over time, the original caulking may crack or deteriorate. Refreshing it helps stop air infiltration.

How to do it:

• Use exterior-grade silicone or latex caulk
• Scrape out any old, damaged caulk before applying new
• Caulk both the interior and exterior sides of the window if accessible
  

Tip: Choose paintable caulk if you plan to refresh your trim after sealing.

4. Install Thermal or Insulated Curtains

Heavy window treatments can act as an additional barrier against drafts. Insulated curtains or cellular (honeycomb) shades trap air and help regulate indoor temperatures.

Best practices:

• Choose floor-length curtains for maximum coverage
• Close curtains at night to retain warmth
• Open them during the day to let in free solar heat
  

Layering with blinds or shades can also improve performance.

5. Add Draft Snakes or Window Seals

Draft snakes—those long, fabric tubes you may have seen on door thresholds—can also be placed on window sills to block cold air. There are also modern silicone or foam seal alternatives that do the same job.

Use them on:

• Double-hung windows with gaps between sashes
• Windows with warped or uneven frames
• Basement or attic windows with poor sealing
  

You can even make your own draft stoppers with fabric and rice or use peel-and-stick options for convenience.

6. Use Rope Caulk for Temporary Sealing

Rope caulk is a pliable, putty-like substance that can be pressed into gaps around window panes or sashes. It’s easy to apply and remove and doesn’t require tools.

Advantages of rope caulk:

• Ideal for renters or temporary fixes
• No mess, no drying time
• Reusable season after season
  

It’s especially helpful for sealing older wooden windows with multiple small panes (divided lites).

7. Install Interior Storm Windows

If you want a more permanent solution without replacing original windows, interior storm windows are a fantastic option. They add an extra pane of glass or acrylic inside your existing window and offer excellent insulation.

Benefits include:

• Significant energy savings
• Noise reduction
• Preservation of historic windows
  

Though more expensive upfront, they offer a great balance between preservation and performance.

8. Use Foam Backer Rod for Large Gaps

For unusually wide gaps that can’t be sealed with weatherstripping or caulk, foam backer rod is a great solution. It’s a flexible, tubular foam that you press into the space before sealing over it with caulk.

Where to use it:

• Along the bottom of window sashes
• Between framing and the wall
• In wide, uneven gaps from shifting or settling
  

It acts as a filler and provides a base for better insulation and caulking.

9. Don’t Forget Window Locks and Latches

Believe it or not, properly locking your windows helps seal them more tightly. Many double-hung or sliding windows have locks that press the sashes together to reduce airflow.

Quick fix: Check that your windows are fully closed and locked—especially during cold snaps.

Final Tips for Best Results

• Test for drafts using a candle or incense stick near window edges on a windy day. Watch for flickering or smoke movement.
• Clean surfaces before applying any adhesive-based product for better grip and longevity.
• Combine methods for maximum efficiency—weatherstripping + curtains, or film + caulk.

Stay Warm with Support from Builders Surplus

Learning how to insulate old windows is a smart step toward better energy efficiency and year-round comfort. Whether you’re sealing gaps, adding weatherstripping, or exploring more permanent upgrades, a few simple improvements can make a big difference.

Need help finding materials or expert advice? Visit Builders Surplus at one of our convenient locations in Massachusetts, Rhode Island, or Connecticut—or call 866-739-1636 to speak with our knowledgeable team. We’re here to help you make the most of your home improvement budget.

Photo by Waldemar Brandt