Clera Windows + Doors Blog

How To Check And Fix Drafty Windows

With the cooler months approaching, having drafty windows and doors can be an annoyance that drives up your heating bills even when using an energy-efficient HVAC system.

Studies suggest that a single drafty window can reduce your heating efficiency by up to 25 per cent. Now imagine the damage to your energy costs if you have multiple windows allowing cold air in from outside.

Sealing air leaks in your windows is a simple chore that can help eliminate cold spots in your rooms, which translates to better insulation and savings in your utility bills. Improving your home’s insulation also makes the rooms more comfortable as you have better control of your heating and cooling system.

Checking for drafty windows

There are several ways to check for leaky windows, though it is best to perform these tests on a windy day or when there is a substantial difference between the indoor and outdoor temperature. Here are a few ideas:

  1. Visual inspectionStart with a thorough inspection of your windows from outside your home, looking for areas where the caulking appears to have failed, revealing the space between the window frame and house siding. If you have single-paned windows, also assess the individual panes of glass for damaged glazing at the edges.From inside your house, inspect the weather-stripping around the windows for signs of damage so you can replace it. Check for cracks in the glass, frame, and sash.
  2. Check for loose windowsTo check if your windows are closing tightly, place a piece of paper on the windowsill and then close it. Try to pull the paper out. If it comes out easily without tearing or folding, it is likely that air can pass through as well, and you should install weather stripping or a new threshold.
  3. Smoke testFor air leaks that are not easily visible, you can conduct a “smoke test”. To prepare for the test, close all doors and windows in your home, and then turn off all combustion appliances, such as the water heater or furnace. Next, turn on the bathroom and kitchen exhaust vents to create an internal negative pressure that sucks outside air into your house through any opening.Now, place your hand in areas that are likely to have gaps to see if you feel the draft on your hand. You can try putting some water on your hand to make the test more effective.

    Alternatively, you can tape a small piece of plastic wrap in a pen and then hold it next to your windows. Make sure that the plastic can move freely. It will be easy to detect any draft from your windows.

    For a more dramatic test, you can use smoke from a lit incense stick. Pass the stick close to the edges of your windows, looking for any noticeable change in the way the smoke rises. If there is a draft, the smoke should waiver and get blown inwards from the outside air leaking inside.

    You can also use a lit candle in place of the incense stick with the same test. If the smoke or flame is undisturbed, you can assume that there are no leaks in that area.

  4. Technical testIf you have the resources, you can try using an infrared thermometer to detect air leaks. This non-contact thermometer can measure ambient air temperatures around your window frames. Leaky areas letting cold air into the house should register a colder temperature than the rest of the room.

Fixing drafty windows

When checking for drafty windows, make sure to go over each window and mark any problem areas so you can go back and seal them later. There are several easy fixes for leaky windows, including:

  • Rope caulk: This soft and sticky substance can be molded to fit the gap. It is also easy to remove at the end of the season
  • V-seal weather stripping: This plastic weather-stripping is added along the sides of sashes. It is very effective, and doesn’t hinder you from opening and shutting your windows.
  • Shrink film: This is a clear plastic sheeting that, when applied with double-sided tape and heated with a hair dryer, shrinks to form a tight seal that prevents drafts. To release the tape in spring, simply use rubbing alcohol.
  • Nail polish: This is a great option for DIYers. Clear polish can fill any cracks to form an invisible seal when carefully applied. Once it hardens, the polish will stabilise the glass enough to make it through the cold months. You can also seal cracks by applying clear weather seal tape.
  • Replace loose or missing glazing: If you notice cracks or signs of wear in the glazing putty that seals your windowpanes, you can replace it. First you will need to remove the old putty so you can detach the pane to add fresh putty. Then press the glass gently into the putty and add glazing points.


Note that these solutions will only work if the window itself is not severely damaged. Replacing the glazing can work for older windows, but if they are worn, rusted or rattling persistently, you should consider replacing them. At this point, you should call the pros.

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