Tag Archives: Damp Prevention

When Ventilation alone will NOT dry the air

Having written an article explaining when just opening a window is enough to dry the air in your home I need to balance that out and explain why just opening a window will not work in unheated spaces.

How to dry your garage properly

Unheated spaces like garages do not benefit from ventilation in the same ways as our homes.

Opening the window to bring in fresh air will work fine if you are heating the room up because by increasing the air temperature you will decrease the relative humidity of that air.  For example if you pull air in from outside at 10°C and 80%rh and then heat it up to 20°C, the relative humidity of that air will fall to around 52%rh.

But what if you need to look after a space that is not heated and contains something that is sensitive to changes in moisture?  This is often the case when you look at garages, archive storage, motor homes, caravans, boats or even your garden shed.  Often these spaces will contain classic cars, bedding, papers, family photo albums, leather upholstery in the cars, veneer, wooden objects, fabrics and expensive electronics.  Lots of things that need protecting from excess moisture and could be damaged beyond repair if they absorb and hold the excess moisture in the air.

If you are not heating the space and air is allowed to come in at our 10°c and 80%rh then it will stay at 80%rh.  It could well be that the internal temperature is slightly higher than the outside the conditions thanks to insulation but unless it is (in this example) 5°C warmer, you will not dry the incoming air below 60%rh to get it into what would be seen as the upper end of a ‘safe’ relative humidity zone by conservation experts.

So although a lot of these spaces are ventilated when they are built this only helps to keep the air moving and to stop the air from becoming stale, it will not help to keep the space dry or to protect the artefacts from moisture damage.

This is where a dehumidifier comes in and why we sell so many dehumidifiers to customers to help look after unheated spaces.  More details on the correct dehumidifier to use in an unheated space can be found here.

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When Ventilation alone will Dry the Air – but not for everyone

We are often told that if you live in a damp home that all you have to do is open the windows to solve the problem, I have lost count of the number of times that I have seen articles about tenants complaining about damp accommodation only for people to comment ‘why don’t they open the windows?’ as a solution to the problems.

So what is the truth about this, is it as simple as just opening the window?

Excess moisture in the home can lead to damp forming around the windows

Will opening the window solve damp problems?

During our normal daily lives we create moisture in our homes by bathing, showering, washing, breathing(!), drying laundry, cooking, arriving home wet etc.  It really is remarkable how much moisture we produce each day.

The problem comes in the winter months when we keep the windows closed and the surfaces of the walls and windows become colder because the outside air temperature is lower.  The moisture becomes trapped within the house and when it comes into contact with the colder surfaces it starts to condense.  This is when we see the problem and when mould is likely to start to grow.  The increase of moisture in the air will also mean that it becomes harder to heat the air, heating bills will go up and the home will feel colder.  If clothes are being dried on a clothes horse then they will take longer to dry because the air around them is damp and the high relative humidity might also result in health issues.

The answer is to get rid of the damp air in order to reduce the relative humidity in the house.

Opening the window will certainly introduce fresh air to the room which could help to dry the air.  The air coming into the space will more than likely be damp, it could well be damper than the air that it is replacing.  This page from BBC weather shows that the average relative humidity in London varies between around 58%rh and 88%rh throughout the year.  Mould grows at 68%rh and condensation can easy form on a cold surface from any relative humidity within that range.

So how will opening the window help if the air coming in is damp already?

  • If you bring fresh air into the house then the same amount of air will leave the house so some of your damp air will be forced out to outside.
  • If the air coming in is colder than the temperature of the house then it will be heated up.
  • If you heat air then the relative humidity of the air falls.

Today in Guildford the BBC tells me that the outside air is 6°C and 74%rh.  If I heat that air up to 20°C then the relative humidity will fall to 30%rh, this is how fresh air can help to dry a space.

But there are other implications that have to be taken into account when looking at the method, the science works but it does not tell the full story on its own.

  • Do I want a cold draught running through my house constantly?
  • How much will my heating bill go up because I am constantly heating this air up from circa 6°C to 20°C and then pushing it to outside once again?
  • Can I trust my children to open the windows after they have had a shower (no!)?

Customers have also expressed other objections to this method

  • Leaving windows open is a security risk for them.
  • They live close to a main road so opening windows brings in both noise and air pollution.
  • Their heating system is not powerful enough to heat the air up quickly enough.
  • They don’t heat all of the rooms in their house.

So the science behind the comment ‘just open the windows’ could work but for many people the reality is quite different and this is why so many people rely on a dehumidifier to remove the damp from the air.

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Bedroom Dehumidifier: The Guide

Customer’s asking for a dehumidifier for their bedroom is a common request, but how do you know if you need a bedroom dehumidifier?

The top 5 problems

1. Condensation forming on windows overnight especially during the winter months.  This condensation might need to be moped up each morning, can create puddles on the window sill and will damage any wooden parts of the window.

2. If you have condensation then mould is likely to form around the edge of the window, the black spots of mould can be difficult to remove once it has established itself.  In extreme cases mould will also form on the walls bordering the windows and if you are really unlucky on north facing outside walls.

3. Dust Mites live in our beds and for many trigger an allergic reaction that causes us to sneeze when we are in the bedroom or if we are really unlikely have an asthma attack or other serious reaction.  This happens when we inhale their droppings.  You can have a similar reaction to mould spores as well.

4. The bedroom has a cold chill about it and is hard to heat in the winter.

5. Built in wardrobes carry a musty smell and clothes become mouldy.

Why do we get these damp problems in our bedrooms?

1. Condensation forms when moisture in the air hits a cold surface.  In the winter our bedrooms will be centrally heated to around 20°C/22°C but the surface of the windows will be cooled overnight as the outside temperature drops.  Warm damp air hitting a colder surface creates condensation.

2. Mould forms when water gets into a surface, i.e. condensation getting into the gaps around a window or moisture in the air getting into the fabric of the walls.

3. Dust Mites reproduce faster when the relative humidity is above 60%rh.  Mould grows and creates mould spores when the relative humidity goes above 68%rh.

4. The higher the relative humidity in your bedroom the harder and more costly it will be to heat because the more water molecules there are in the air that have to be heated up before you can start to feel warm.

5. Built in wardrobes, especially those on north facing outside walls, suffer because the damp air from the bedroom enters the wardrobes, hits the cold surface at the back of the wardrobe and then mould forms.  The musty smell comes from the mould.

Is this damp damaging to our health?

Dust Mites and mould spores can create serious allergic reactions when we breathe them in, whether that is asthma, other respiratory reactions or eczema.

I did have one customer who rang up once and said that water dribbled out of her bed when she got in (it was not a water bed) and another who had a mushroom growing on her mattress!  You don’t need to be a doctor to work out that this is not good.

Is this damaging for our wealth?

Having a high humidity in your home pushes up your heating bill because you need to use more energy to achieve your desired room temperature.

Treating mould means buying mould remover, dealing with dust mites might mean buying an expensive vacuum cleaner or cleaning your sheets on a more regular basis at high temperatures.

Musty wardrobes and mould growing on clothes results in clothes and shoes being thrown away or washed on a more regular basis.

So what is the solution?

You could open your windows more but you have no way of knowing if the air outside is damper or dryer than the air inside and in the winter the air will be cold, which is not pleasant, and it will need to be heated up – which costs more money (and then this cycles repeats itself all day long).

Turning up your heating will just cost you more on your energy bills and will not remove any moisture from the air.

Buying and using a dehumidifier will solve all of these issues.

Why will a dehumidifier make my bedroom better?

1. A dehumidifier removes the excess moisture from the air which reduces the relative humidity.  If the relative humidity is lower then condensation should not form on the windows.

2. Mould spores will not be created and you should get less mould around the windows and on the walls.

3. The dust mites will slow down their reproduction rate so there will be less droppings in the air for you to breathe in.

4.  The air will be easier to heat because their will be less water molecules in the air and your heating bills will drop.

5. Built in wardrobes will dry out so mould will not grow and the musty smell will go.  Your clothes should become mould free.

Where do I put the dehumidifier, do I have to sleep with it?!

To dry your bedroom you do not need a dehumidifier in your bedroom.  We put ours onto the landing and leave the bedroom doors open during the day.

To start off with it might be a good idea to put it into the bedroom during the day and to leave the wardrobe open to let the dry air circulate.

Which dehumidifier should I buy?

Base the dehumidifier on the size of house, our guide will walk you through the selection process.

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Does your door jam in spring?

I noticed the bathroom door was sticking this morning, not something that has troubled us over the winter, so why now in March is it suddenly sticking?

Because I am no different to everyone else and sometimes I don’t follow my own rules (and I get lazy!).

In winter it is easy to see the effects of excess moisture as it condenses on our windows and this drives us to use a dehumidifier.  As the weather warms up in Spring we get less condensation on the windows and we are more likely to open the windows to clear any condensation because the draught from the open window will not be as cold as it is in winter.  With less troublesome condensation to deal with we see less of a need to run a dehumidifier and it spends more time turned off.

But just because we cannot see the moisture on the windows does not mean that it is not there and with the windows that bit warmer we no longer have a reliable indicator as to whether the relative humidity is too high.

Well actually we do – the dehumidifier. 

If the dehumidifier had been left on then it would have turned itself off when the relative humidity was acceptable and then turned itself back on when the air needed drying.  In my case the tank filled up with water, the dehumidifier turned off and for reason I did not get round to emptying the dehumidifier for three or four days.  These three or four days were long enough for the bathroom door to start jamming.

Meaco Platinum Range dehumidifier

The Meaco Platinum Range has a display to show you the current relative humidity. If I had looked at mine then I would of realised that it needed to be turned on!

So why did the door start to jam just because the dehumidifier was turned off?

The door is made from wood and wood likes to be in equilibrium, with its surroundings.  This means that as the relative humidity increases the door ‘breathes’ in more of this moisture so that its own internal relative humidity is the same as the air around it.  If the door takes on more moisture then this makes it bigger and of course if the door swells up then it starts to jam.

So the solution is for me to run the dehumidifier and to leave it turned on because even if there is no condensation on the windows other things still need looking after because the door is symbolic of all of the other organic materials in the house that will be taking on the Spring moisture – books, pictures, clothes, tools, furniture etc., none of which I want to start showing signs of mould growth.

So I will try and follow my own advice and leave the dehumidifier on and for those who are new to dehumidifiers and damp try listening to your door, it could be telling you that you have humidity problem this spring.

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Dehumidifier review – reading between the lines

I was reading an online dehumidifier review recently whereby an Ebac customer returned his dehumidifier because he had no condensation for the first week or so of using it and then the next morning he had condensation.  The dehumidifier was blamed and returned for a full refund and the customer posted a bad review of the dehumidifier. 

Ebac have been hard done by here and if the customer knew a little bit more about dehumidifiers and condensation then he would not have returned the dehumidifier or posted the review.

So what happened?

The dehumidifier was collecting water and achieving a relative humidity in the mid 50’s which was sufficiently dry enough to prevent condensation from forming on the windows.  The next night the temperature dropped outside and the windows became colder and when the homeowner woke up there was condensation on the windows.  The relative humidity in the house was still in the mid 50s so nothing had changed in the air, all that had changed was that the windows were colder.

So who should we blame?

We could blame Mother Nature for the temperature dropping outside, we could blame the quality of the double glazing for allowing the temperature of the inside pane of glass to fall but we shouldn’t blame the dehumidifier because it had remained constant and held the relative humidity exactly where it had been asked to.

But why the condensation, it is a dehumidifiers job to prevent condensation?

All a dehumidifier does is to reduce the relative humidity of the air by removing moisture from the air.  Whether or not you get condensation on the window in the morning is a relationship between three factors;

  • Room air temperature
  • The surface temperature of the glass
  • The room relative humidity

The dehumidifier can only directly affect one of those (it might affect the air temperature a bit depending on room size).

So let’s say in our example that the room temperature is 20°C and the relative humidity is 55%rh.  As long as the window temperature remains above 12°C then condensation will not form.  But if the surface temperature of the glass falls below 12°C you will have condensation.  It is simple as that, the dehumidifier may well keep the room humidity stable but the winter weather makes the glass colder at night and hey presto you have condensation. 

Who gets blamed – the dehumidifier.

So what should the reviewer of done to prevent the condensation? 

Well installing new windows is obviously not practical (at least overnight!) so he could have set the dehumidifier to achieve a lower relative humidity, leaving the heating on a bit overnight will stop the room temperature from dropping too low (as temperature drops relative humidity increases) and leaving the curtains open would of allowed the air to circulate around the window more (especially useful if the room door is left open and the dehumidifier is running at night).

All of this tells us that dehumidifiers/condensation/damp can be confusing.  If you are stuck and struggling to get the best out of your dehumidifier then feel free to email me via askaquestion@meaco.com or just call the office on 01483 234900 and we would be delighted to help you.

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