What causes that draft? OK, you know you could deal with the problem for now by grabbing a sweater or a roll of duct tape. But what about the long term solution and the other windows and doors? Do you have 10 minutes and a couple of matches? OK, lets figure out how to fix all the drafty windows so they stay fixed, don’t disturb your comfort or heating bill again, and get the answer now. Obviously there is a hole, or crack or slightly open window or door, but that isn’t the cause, it is a path for one draft. If we block that path, another will pop up – like whack-a-mole. The driving force is air pressure difference between the outside and the inside. So what is the ultimate fix for drafty windows if it’s not simply plugging the hole?
Of course you can caulk the crack, or fill the hole, replace the loose window or install storm windows, and that might block the draft you felt, or it may not be the path that caused that draft. If you want to truly fix the draft, you must get to the root cause. When you see how to find and fix that root cause, your drafty window days are over.
How to find the ROOT CAUSE
Actually, finding the root cause is a surprisingly easy bit of detective work. If the driving force is pressure in the house different from pressure outside, then the root cause is whatever caused that pressure difference. Fortunately there are only 3 possible drivers for this house pressure problem:
- something is pumping air out of the house,
- something is pumping air into the house or
- wind creates pressure differences at each window, pumping air in or out.
You must find which of these three is the cause of the pressure difference that creates your draft. That’s easy if you have a candle or a match.
You must use the smoke to see where your draft is blowing. Is it blowing toward the window? If so, the pressure is higher in the house, at least it’s higher close to the window. Do this test by other windows including at least one on the other side of the house. Do all the drafty windows have drafts blowing toward them? The answer to this question tells what type of “pump” is the root cause:
- All drafts blow toward a window, door or wall – then air was Pumped IN
- All drafts blow from a window, door or wall – then air was Pumped OUT
- If drafts blow in different directions – then air was Pumped by the wind
The negative pressure building
In most cases this test will show that the house pressure is lower, and air is being pumped out. The reason why building pressure can be negative (lower than outside), is that things like exhaust fans in the bathroom or kitchen and dryer vents, chimneys or flue pipes from gas hot water heaters or fireplaces pump air out of the building. If something else doesn’t pump air back into the house, then the pressure in the house becomes negative. Many homes and other buildings have negative air pressure inside because of devices exhausting air out without bringing fresh air in.
If the problem varies in direction, window to window, then the average house pressure is not negative, it is just a local problem due to wind against a wall or a window.
If all drafty windows and doors have air flowing toward them, then there is a strange and possibly dangerous situation. This can be caused by open fires without a functioning flue or exhaust, or a gas leak into the building. Such situations can cause toxic or explosive gas buildup in the building, so they should be treated as emergencies.
Determining the ultimate fix
If you have a positive pressure house, please get people out until the furnace repair, gas company or chimney sweep can assess and correct the problem. The potential for carbon monoxide poisoning or fire is too much risk to be worth taking chances. This could kill off brain cells or even end a life!
If the problem is the wind, then adding or improving barriers blocking the wind deals with the root cause and solves the problem. Wind can be blocked by caulking and sealing, storm windows or a stand of trees to shelter the drafty wall, depending on the details of your situation.
But often the problem is a negative pressure house, and it requires a way to pump air in so that it doesn’t leak-in driven by higher pressure outside. There are special furnace and fireplace vent systems designed to do this, but they might not move enough air to make up for dryer vents, range hoods and other exhaust systems. A more comprehensive solution is a vent fan that brings air into the home, either unconditioned or filtered and temperature controlled. You could consider a *Heat Recovery Ventilator (HRV) like this one available through Amazon, or a similar system sized specifically for your building.
You could try a DIY approach combining changes to your exhaust devices, fans, filters and heat-exchangers you assemble in a custom scheme for your situation. Whether you buy a package unit or use a custom approach, it is probably good practice to do some caulking and sealing as well, as this will also improve the heating and cooling efficiency while helping avoid drafts that could arise in windy conditions.
*NOTE- Some items in this post are provided by sponsors who support this website – see our sponsorship page for details.
Share your drafty window story
Please tell us about what you found in your drafty house or with your drafty window situation, or if you get stuck, ask for help. If you had a problem with our “Ultimate fix” or with the root cause diagnosis, let us know, so we can try to offer alternatives. In any case, please share your experience and join in the conversation so we all get smarter about drafty windows and homes, and how to fix them completely.