Window Sealing

There is nothing better than standing by your window looking at a winter storm raging outside and feeling warm and snug in your comfortable home, except when your windows are leaky and drafty and you feel cold drafts in winter, or hot moist air in summer.


  • Cold air finds its way through small and large gaps and cracks in the window frame and window surround and infiltrates directly into your warm space.
  • Even double or triple-paned glass windows insulate less well than the average wall…so the interior surface of your window tends to be cold, and heat from your body radiates towards that cold area.
  • The colder interior glass surface of the window cools down the air in your room adjacent to the window, and as a result that body of air tends to fall to the ground and create a draft.
The Right Window Sealing Options for Your Home

There are many different approaches to reducing leaks and loss of heated or cooled air around windows. Here are some of our favorites, running from the cheapest to the more expensive:

  1. Caulking gaps and cracks in the window frame and surround.
  2. Applying plastic film to the interior of the window with double sided tape.
  3. Weatherstripping.
  4. Installing interior window treatments: blinds and curtains.
  5. Installing exterior or interior storm windows.
  6. Removing the window framing to upgrade insulation around the window.
Which Options are Right for You?

Here are ways to figure out how to improve your windows:

  1. Do your own diagnosis:
    • Make sure the basics are good: take out window air conditioning units for the winter and systematically make sure all the windows are closed and locked and, if you have storm windows, make sure they are also down and locked.
    • Use an incense stick or just a wet finger and move it around the window frame on a cold windy day to find out where the leaks are: identify where there are gaps that can be caulked.
    • Check whether your windows are single-pane or double pane: if they are single pane, and there are no storm windows, you need to take action to increase the low insulation effectiveness of single pane glass: plastic film at a minimum, storm windows and window treatments if you can afford it.
    • If your windows open, check whether there is weather stripping or an integrated design to minimize air movement between the window and the window frame; if not, check out our guide to weather stripping and get to work or get a friend to help out.
  2. Get Advice:
    • Find a local expert on windows who can take a look and give you advice; there may be someone who is prepared to help you at no cost because they are so committed to helping people save energy.
    • Don’t get advice from a salesman for a window company! Their agenda is to sell you windows, not to tell you how to make your current windows more efficient.
Caulking Gaps and Cracks in the Window Frame and Surround

One of the best methods for sealing your windows against chilly winter drafts is to apply silicone or latex caulking. Place a tube of caulk in a caulking gun, run a bead of caulk wherever you detect a gap that is allowing air to flow and smooth the caulking with a wet rag, your finger or a smoothing tool. This option is inexpensive; quality caulking can last for several years and generally pays for itself in energy saving within one year.

More on Caulking

Applying Plastic Film to the Interior of the Window with Double Sided Tape

3M and others manufacture inexpensive window insulation kits. You use double-sided tape to position a sheet of plastic film to the inside of your window and then shrink the plastic and eliminate any wrinkles with hot air from a regular hair dryer. This has the advantage of being one of the least expensive and simplest options, but it can be visible on the indoor frame of your window and will only last for one season, or until you choose to open your windows again. Even if it only lasts one season, you will more than make back your money!

Weatherstripping the Window

Most modern windows have overlapping strips and connectors to automatically seal gaps between sections of the window and between the window sections and the frame. For older windows there are many types of weather stripping that you can apply which will reduce leaks substantially. The process to install weather stripping depends on the type of product you choose, but most weather stripping can be easily applied by pressing pre-measured, adhesive strips against the inner and outer sashes of clean, dry windows. Like caulking, high quality weather stripping can last for many years.

See more on weatherstripping options here.

Installing interior window treatments: blinds and curtains

Curtains and blinds are the old-fashioned way to cut down drafts and warm up a room. And today there are high performance insulated shutters and shades that really make a difference. For instance there are Hunter Douglas shades, which qualify for the recent federal energy efficiency tax break.

Installing Exterior or Interior Storm Windows

If you are able to spend a little more on your project to increase energy efficiency in your home, you may want to install storm windows. The cost is higher than the other fixes we have discussed so far, but if you install a quality storm window on an existing single pane window, you can expect to get your money back in energy savings in 4 to 6 years. Storm windows are available for most types of windows and they can be installed on the interior or the exterior.

Removing the Window Framing to Upgrade Insulation around the Window

The performance of your windows depends not just on the quality of the windows themselves, but also on how well they were installed. In particular, if your installer did not really understand the importance of insulation or had not been fully trained in how to ensure that the areas around the window are well-insulated, then you may have windows where there are highways for cold air to travel and find cracks and gaps to enter your home. A qualified local energy enthusiast or professional with access to a thermal camera can use it to examine your windows and diagnose if this is an issue you need to address.

Behind the Walls
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Cambridge, MA 02142