Do you have condensation on the outside of your windows? This simple rule of thumb determines if it's normal, or a sinister warning sign

Condensation forms on windows when there is a temperature difference, causing water droplets to gather on the surface. If you're wondering whether it's normal for condensation to appear on the outside, our HVAC pros have the answer.

As long as yours clears as the day goes on, it isn't an issue. If it sticks around, combating window condensation on the outside may be an indicator your insulation is failing.

Why does condensation form on the outside of windows?

Condensation most commonly forms on the outside of windows when air inside your home is significantly warmer than air outdoors. The difference in temperature results in condensation developing on the cooler side outdoors.

'When the air reaches its dew point – the temperature at which it can no longer hold moisture – water droplets form on the glass,' says Josh Mitchell, a HVAC Technician at Air Conditioner Lab. 'You’ll usually notice this in the early morning or late evening, especially in spring and fall. During the night, the temperature drops, and by morning, the air warms up again while the window surface is still cold.'

Window condensation usually forms during the winter, especially when you sleep. Whilst stopping indoor condensation on windows overnight can be tricky, outdoor condensation isn't anything to worry about unless the condensation doesn't clear.

If you live in a particularly humid area with frequent rainfall and little direct sunlight beaming onto your windows, condensation developing on the outside of your windows may be a more common occurrence, too.

Opening your windows regularly to improve ventilation in your home and sitting a small dehumidifier like this 95oz Quiet Dehumidifier with Reusable Filter from Amazon on your windowsill can help with this if the condensation is obscuring your view.

Josh Mitchell

Josh Mitchell is an experienced HVAC technician, and his detailed knowledge extends across AC and heating systems, air purifiers, dehumidifiers, and humidifiers. He helps people troubleshoot and fix their HVAC system problems.

Is outdoor window condensation problematic?

If condensation is forming on the outside of your windows occasionally and not the inside, it's not a problem. In fact, it's a sign that your heating and insulation is effective, keeping your home warm all day and successfully retaining heat indoors.

'Condensation forming on the outside of windows generally is harmless,' says Josh. 'Unlike condensation inside your home, increasing the risk of mold, water damage, and air quality issues, exterior condensation is just a temporary effect of temperature and humidity changes. It typically evaporates as the day warms up.'

But if the condensation on the outside of your windows is always there and doesn't naturally dissipate during the day as temperatures rise, it could be an indicator of an insulation issue and a warning sign of mold and rot problems down the line.

Ernie Cappello, CEO of WindowFix, says, 'While there’s no problem with condensation on the window glass itself except visibility being obscured, that moisture could seep into wood trim around the windows and lead to mold and rot if it doesn't naturally dissipate throughout the day. Even worse, it could be an indicator that condensation is also occurring within your walls, which can lead to unhealthy mold, or a sign that your windows are surrounded by poor airflow.'

Ernie Cappello

Ernie Cappello has been repairing and replacing windows since he started working with his father, company founder, John Cappello nearly 40 years ago. Since then, WindowFix have repaired or replaced over a million windows across New York City. Ernie has highly specialized training including: AAMA Certified Installer Residential & Commercial, BPI Energy Star Home Performance Contractor, Passive House Certified Tradesperson, Marvin Window and Door Certified Installer, Andersen Window and Door Certified Service Dealer, and is a Provia Certified Installer.

What can you do about outside window condensation?

If the condensation on the outside of your windows fluctuates, naturally disappearing as the day unfolds, you don't need to do anything. But if it lingers or remains constantly present outside, there are a few tricks you can use to banish it from your windows.

Firstly, if you use dehumidifiers in your home, check whether they're on the right setting and consider the best place to put yours.

As noted by Bob Zee, owner of New Panes Creations, 'If your house is warmer than the outside air and has high humidity it can cause condensation,' so it's important to do what you can to maintain good humidity levels in your home.

An affordable hygrometer such as the ThermoPro TP49 Digital Hygrometer from Amazon is a great idea, as its sleek display will monitor your home's temperature and humidity levels so you'll be alerted when you need to reduce your home's humidity.

Doing simple things to increase the airflow around your outdoor window as well will help condensation to disperse throughout the day on its own, including shock ventilation and creating moisture channels.

'If trees or shrubs are too close to the house, they might prevent moisture from evaporating quickly,' says Josh. Trimming these back out of the way will allow both air and sun to combat the condensation more effectively.

And lastly, if you're still struggling to curb the condensation on the outside of your windows, Josh recommends applying a water-repellent glass treatment such as the Rain-X Glass Treatment available on Amazon to the surface of any windows panes facing the problem.

'Rain-X Glass Treatment creates a thin, invisible coating that makes moisture slide off the glass instead of forming droplets,' says Josh. 'It’s commonly used for car windshields but works just as well for home windows.' This way, condensation won't even have a chance to form.

The easiest way to apply a glass treatment like this to your window panes is to rub small amounts at a time into the surface using a microfiber cloth like the MR.SIGA Microfiber Cleaning Cloths from Walmart, which won't scratch your windows in the process.

Bob Zee

Bob has been the owner of New Panes Creations for 10 years, taking the window and patio door company over from his father but has been in the industry for 35 years. New Panes began in 1975, and helps up to 3,500 customers per year.

FAQs

Why does the outside of my window have condensation but my neighbor's doesn't?

There are many reasons why the outside of your window may have condensation but your neighbor's doesn't, including differing home temperatures, different levels of home humidity, and different kinds of windows and insulation types.

Josh Mitchell, a HVAC Technician at Air Conditioner Lab, says, 'Some homeowners wonder why their windows have condensation while their neighbors don’t. The answer usually comes down to insulation. If your windows are newer and well-insulated, they trap more heat inside, making the exterior surface cooler. If your neighbor has older windows, more heat escapes, keeping their outer glass warm and reducing condensation.'

If you're looking to add some greenery into your home and have been battling with indoor condensation, these houseplants that help banish condensation are the perfect addition to your space and will help absorb surplus humidity.

Next, learn more about what the humidity level should be in your house in winter.