As I write this the temperature in Guildford is dropping down to -5°C or worse and the skies are clear and blue. When I touch my car there is a spark of blue as a static shock is generated, and then of course, there’s the condensation. This is one of the biggest problems homeowners face. So, can you cure condensation?
Opening Windows To Deal With Condensation
The two main approaches to ‘curing’ condensation are either to open the windows or use a dehumidifier. You would probably expect me to recommend that you buy a dehumidifier. I am a dehumidifier manufacturer after all. But let’s look at the benefits of opening windows first.
When people worry about condensation or mould problems, the advice will often be to open the window. This is to improve ventilation – and in some older properties that are often quite ‘leaky’, we can see that condensation is rarely an issue. So why does ventilation help?
Opening windows can cure condensation – but do you want to let the cold in?
First, what is condensation?
Condensation occurs when air hits a surface that is cold enough for condensation to occur. It doesn’t matter how little moisture there is in the air – if the surface is cold enough you will get condensation. This is why when my windows at home have been condensation free for months, I am now suddenly getting condensation when it’s very cold. I doubt that the amount of moisture in the air in my bedroom has increased. It is just that the surface temperature of the window is lower during a cold spell.
Condensation forming on cold surfaces happens because of the inverse relationship between temperature and relative humidity. As temperature falls, relative humidity increases and as temperatures rises, relative humidity falls. So if you heat air up the relative humidity will decrease. This is the key to the reason why ventilation can help cure condensation.
What happens when you open the windows?
The air in your home is full of moisture from cooking, bathing, showering, drying washing and even breathing. The air outside in winter will probably have a lower relative humidity or even if its relative humidity is higher it will be colder. So when you open the windows, warm, damp air goes out and cold air comes in.
So, your room is now a lot colder, which may seem good. But you don’t know whether the relative humidity of the air has changed. If we have no control over the relative humidity of the air coming in, and if the relative humidity of this new air is higher, have we helped the situation?
The answer is still yes. That’s because we are not going to let the air stay cold: we will heat it up to a temperature that we are comfortable with. If the air outside is below freezing and I want it to be about 20°C in my house, I will warm it up. Even if the air coming in is full of moisture and was to have a relative humidity of 90%rh, warming it up will reduce that relative humidity right down to something like 25%rh.
So, all is good! We have got rid of our warm damp air, replaced it with cold damp air and changed it to warm dry air. That is a cure for condensation.
Opening the windows works and is an effective solution to condensation control.
But
Think about what we have just done. We have heated the air, costing us money, and then we have thrown that heated air out of the window. It might have been easier to throw fivers into the street!
To replace it, we have introduced freezing cold air into our home and made ourselves feel very uncomfortable.
Now we have to heat the new cold air to make ourselves feel comfortable again and to reduce the relative humidity. This costs more money in energy, and later in the day, we’ll probably have to do it all over again. In fact, ideally you will have to do this in every room in the house. You will certainly need to do it in the bathroom, kitchen and bedrooms at the very least.
Opening the windows does work but I am not a fan because it makes people feel uncomfortable and has this huge hidden cost in terms of money spent on heating the air up and then reheating the fresh air coming in from outside. With energy bills sky rocketing it seems a real waste of money to keep on throwing the energy outside.
Is a dehumidifier a better cure for condensation?
Running a dehumidifier does of course have a cost to it. There is an initial outlay to buy the unit, and then you need to run it. But there is a fundamental difference between the money spent on running the dehumidifier in the home and the money spent of heating air that is then allowed to escape out of the window.
We use our dehumidifiers mainly in the winter when condensation is at its worst. In the winter it is cold and we need to heat our homes. The energy used by the dehumidifier is returned to the room that it is standing. And that energy is in the form of warmer air. So the cost of running a dehumidifier is retained within your home. If you have a radiator within the same space as the dehumidifier, you can turn it off – helping to keep your energy bills down. So where is the cost of running the dehumidifier if you are benefiting from and enjoying the heat that it generates?
A dehumidifier is a fast, effective and cost-efficient way to cure condensation. Opening the windows may seem to be the easy – and free – solution, but it’s not quite as cheap as it looks.
180 Responses
Hi Chris,
We have the usual problem of finding windows heavily misted up and dripping water in the morning when we get up. But it’s not a problem every morning. Sometimes there’s nothing at all, which makes me wonder if climate or living near the coast is the problem. We also have suspended flooring in our 2 bed bungalow with a 1m void under the floorboards/joists where the air would presumably be similar to that outside. My obvious question is will a dehumidifier solve the problem. Our total floor area is approx 70m2, so would the Arete 20L be the best choice?
Hi Bill,
Thanks for your message. The condensation build up on your windows in the morning consist of a few factors, please see below:
1: If it’s been a cold night and the surface temperature of your windows are therefore colder, you are more likely to get condensation.
2: On the days whereby there are more of you in the house, doing things which generate more moisture in the house such as, cooking, exercising, bath/showering, kettle use and drying laundry etc. The more this happens, the more likely you will get condensation.
3: On cold days if you leave windows open, combined with having heating on in the house then you are less likely to get condensation.
When the indoor humidity levels are high, when this humid air comes into contact with the cold surface of the windows overnight, then you’ll then develop the condensation in the morning on your windows.
Whether the Arete 20L is right for you depends on the number of people in your house and the activity levels as mentioned above. Feel free to reply to this and I can establish if the Arete 20L is right for you.
Kind regards,
Omar
Hi Bill, we moved into our new build last year (small 3 bed with 2 adults and 2 children) and last winter the condensation on the windows in the mornings were terrible and I had to wipe every widow down with a towel and mould spores formed around the windows. We do not need our heating on much at all because the house is so well insulated. I would only need a dehumidifier on over night to combat this issue and also for drying laundry. Would the dehumidifier get rid of the condensation in the bedrooms if the bedroom doors are closed? Would I need to position this on the upstairs landing or could this be left on downstairs in the hallway near the stairs to do it’s job? Also, could you recommend which Meaco dehumidifier would be best for this purpose. I have researched a lot and Meaco is definitely the brand I want to buy.
Thank you! 🙂
Thank you for your enquiry,
I’d recommend using at least a 12L capacity dehumidifier.
Doors should be open in order for the air to flow and for your machine to be able to extract the moisture from the room.
Positioning the unit in the hallway is generally a good idea, it allows the machine to be in a fair reach for the rest of the home, permitting internal room doors be left open.
Have a look at our AreteOne 12L for this purpose: https://www.meaco.com/products/meacodryarete1-12l
Omar@Meaco
Hi Chris, thank you for this article. We live in a 3 bedroom 2 story house 70 m2 and we usually had 60+ humidity in the house + condensation around 2 cm at the bottom of each window. We have bought arete 20l and humidity is now around 50 – thats really great, but still there is some condensation on windows. What would you suggest we can do to get rid of it? Should I make humidity less? Thanks
This is telling you that the window is very cold and it still condenses at this low humidity (probably an older window, so less energy efficient). The problem will probably disappear when the overnight temperatures warm up later in the week. You could reduce the humidity to 40%, or just live with it until the weather improves.