Door and Window Sealing: Keeping Cool Air In and Hot Air Out

Know the most common areas to check

If you suspect your home has a leak, your windows and doors are the most likely culprits. Mail slots, door jams, weatherstripping, and other weak points could create small openings for outside air to slip through. 

While you’re checking your windows and doors, don’t forget some of the other most common leak points. That includes: 

• Outdoor water faucets
• Electrical and gas service entrances
• Fireplace dampers
• Attic hatches
• Wall- or window-mounted air conditioners
• Cable TV and phone line access points
• Where dryer vents pass through walls
• Vents and fans

Look for gaps

Visual gaps are a clear sign of a leak, and they’re especially common around mail slots, pipes, and wires entering the home. 

Check your current caulking and weatherstripping

Caulking and weatherstripping can wear out over time, so visually inspect them at all potential problem points. Gaps and cracks are signs of a potential leak, and signify that your home could be a good candidate for window sealing.

Look for light

Here’s a test that’ll involve a partner: Once the sun has gone down, turn off the lights in the house and grab a flashlight. Move to each potential leak point and aim your flashlight through the wall at the potential leak point. Have a partner inside the house look for your light. If they can see your flashlight through the wall, you have a leak. 

Try to rattle them

Grab both sides of a door frame or window frame, and try to rattle it in place. If there’s any sort of movement, it generally indicates some sort of gap that could potentially allow air to pass through.

Try the dollar bill test

This is an easy way to check your windows: Place a dollar bill on the ledge of an open window, then close the window on top of it. If you can slip the dollar bill out of place, your window doesn’t close tight enough for a strong, reliable seal. 

Try the pressurization test

A pressurization test is a clever DIY strategy that uses physics to find your leak. Here’s how it works: Pick a cool, windy day and turn off all combustion appliances (like gas burning furnaces and water heaters). 

Next, shut all your windows, exterior doors, and fireplace flues, then turn on all exhaust fans that blow air outside. 

After that, light some incense and move it around the edges of common leak sites outside of your home. If you spot the smoke being sucked into your home, you have a leak!

Remove the trim

Use a pry bar to separate the trim from the wall. Set this aside; you can reattach it once you seal the windows.

Remove old caulk

Use a putty knife to pick and pry away old caulk. 

Apply spray foam to large gaps 

If you have large gaps (anything over ¼ inch), use low-expansion foam. 

Add weatherstripping

For further protection, apply weatherstripping to give your home an extra barrier from outside air. 

Apply caulk to small cracks

For cracks ¼ inch or smaller, apply caulk and smooth with your finger. Be sure to wear gloves!

Reapply the trim

Once your caulk is in place, reattach your trim.