If you wake up to condensation on your windows – despite having one of the best dehumidifiers – you might be feeling a little confused. After all, isn't that one of the things they're designed to remove?
However, while these damp-busting machines work wonders for removing excess moisture from the air, they're not a magic fix for every condensation problem – with things like their placement, capacity and filters affecting the results.
To find out why your windows are still wet while using a dehumidifier, our air quality experts have shared five potential reasons below.
1. You have a significant moisture problem
Dehumidifiers do a fantastic job of removing excess moisture from the air, but they shouldn't be treated as the only fix. You'll also need to find out whether (and why) you have a ongoing moisture problem.
“If the problem persists, look for a hidden source of moisture," says Simon Trenerry CSDV, Technical Manager at Safeguard Europe. "That could be a leak, penetrating damp coming through a wall, new plaster or screed that’s still drying out which can sometimes take months in new homes, or rising damp.”
Have a look around your home for visual signs, such as mould and mildew, as well as any accompanying musty smells, lifted flooring or peeling wallpaper. If you're struggling to work out where it's all coming from, it's worth getting a professional survey.
This pocket-friendly moisture meter will help you identify damp and condensation issues in wood and building materials.
Simon is a Certified Specialist in Dwelling Ventilation (CSDV) and since joining Safeguard in 2022, he has built a strong reputation among building and renovation contractors for his expertise in diagnosing damp and mould issues and advising both professionals and homeowners on effective solutions to create safer, healthier homes.
2. The type of windows you have
If your type of window has single glazing, older double glazing or aluminium frames without a thermal break, Simon Trenerry says they could be the reason behind your condensation.
"[They can] get so cold on a winter night that they attract condensation even when the room’s humidity is reasonable," he explains. "A dehumidifier lowers the moisture in the air, but it can’t warm up the glass, so upgrading to modern, thermally efficient glazing is the long-term fix."
3. You're using your dehumidifier incorrectly
If you're using your dehumidifier incorrectly, it's going to impact how effectively and efficiently it runs, which could lead to condensation forming more than it should.
Here are some of the most common dehumidifier mistakes:
It's the wrong capacity for the room: Before investing in a unit, you'll need to check that its the correct size for your room – many brands will state the recommended capacity to make this easier. "A smaller model might not be powerful enough for the job," says Chris Michael, founder of Meaco.
It's in the wrong position: This might sound obvious, but make sure your dehumidifier is in the best place, such as the same room as the problem – or leave internal doors open to allow air to circulate, recommends Simon Trenerry.
It's not been running long enough: The condensation might be forming because you're not leaving your dehumidifier to run long enough each day, says Chris.
The filter is blocked: If your filter is blocked or dirty, Chris says it won't be able to do its job properly. Always ensure you turn off the device before checking or changing it though.
Your dehumidifier isn't running when the moisture builds up: "A lot of people run their dehumidifier for a couple of hours in the evening and then switch it off," says Martyn Fowler, founder of Elite Renewables. "But if you've got two people sleeping in a bedroom with the door shut, they're still adding moisture to the air throughout the night. So really you want to check the humidity levels first thing in the morning as well."
Our favourite dehumidifier for tackling damp and condensation, this 20L unit is energy-efficient, easy to use and doubles as an air purifier.
Founder of Elite Renewables, Martyn Fowler is one of the UK's leading renewable technology experts, working with heat pumps for the last 2 decades. His passion for decarbonisation matched with a deep technical experience of the technology make him one of the industry's go-to experts for all things renewable.
Chris and his partner Michelle started Meaco in 1991. Meaco is now regarded internationally as a major player in the dehumidifier industry selling to 20+ countries throughout Europe, North America and South Africa. Meaco sets the benchmark for quality and development in its sector, leading by example and reducing the energy consumption of its appliances.
4. Your curtains and blinds are shut
“Curtains and blinds can make things worse. Heavy curtains or closed blinds trap a pocket of cold air against the glass, which is why window condensation is often at its worst first thing in the morning," explains Simon Trenerry.
With this in mind, he recommends opening them as soon as you wake up and, if you can, leaving a gap at the bottom overnight. It's also worth aiming for a low, steady temperature in your bedroom to prevent it from getting too cold, as well as keeping trickle vents open and airing the room each morning.
5. Your window has a cold spot
If your window condensation is appearing at the bottom or around the edges of the glass, Martyn Fowler says this can give you a clue to the cause.
"The edges of double-glazed units are often colder than the centre. That's why you sometimes get a wet strip around the frame even when the middle of the glass is dry," he says.
While a dehumidifier will help to reduce the moisture in the air, Martyn explains that it's not going to be able to remove the cold spot – and you'll need to investigate the glazing and window seals if it's an ongoing issue.
The underlying advice is that a dehumidifier can only do so much if you haven't addressed the root cause of the condensation.
Found this helpful? You may also want to read our guide on how dehumidifiers work or discover the best type of dehumidifier for cold rooms.
