During cold spells in winter, it is obviously sensible to keep windows in the home tightly closed. However, modern houses and flats are far better insulated and sealed than in the past so, with no air conditioning, this results in a gradual build up of moisture inside the home.
Common signs of this problem are that the insides of your windows, even if double glazed, are wet and mould will start appearing around windows or ceilings, particularly in bathrooms.
This moisture comes from washing machines, showers, cleaning and even the breathing of occupants of the house. Yes even your sleeping cat and the guinea pig are contributing to the moisture build up.
If you don’t have air conditioning then the humidity (moisture in the air) in winter will often increase to levels well above 50% and the house will become damp and black mould and mildew will start to grow.
Ideally, for maximum comfort, humidity in the home should be from 30% to 50%. Anything over 50% also encourages pests such as clothes moths, dust mites, fleas, cockroaches and woodlice. Humid conditions may also lead to a musty smell and cause damage to furniture and carpets.
In addition, drier air feels warmer and less energy is needed to heat the home than when the air is too moist. On the other hand, if the air is too dry, with a humidity of less than 30%, then static electricity becomes a problem and dry air can lead to a dry cough or respiratory problems.
So what is the solution to excess domestic humidity?
Simple. Buy a domestic dehumidifier. There are plenty of models available to suit every size of home. The easiest way is to buy online. Most suppliers in the UK deliver free of charge.
A smaller, bottom of the range machine can be bought on Amazon for around £100 ($150). Something suitable for a 4 bedroom house would start from around £150 ($220).
There are 2 broad types of dehumidifier based on different technologies:
- Refrigeration Dehumidifier
- Desiccant Dehumidifier
Don’t get confused between a humidifier that adds moisture to the air and a dehumidifier that removes moisture.
Refrigeration dehumidifiers, the most common type, typically draw moist air over a refrigerated coil using a small fan. As a result some of the water in the air condenses on the evaporator coils, and drips into a collecting bucket. The dried air is then reheated to the ambient temperature of the room.
This process works most effectively with higher ambient temperatures and with a higher humidity. The process is less effective in a colder location. These machines work best at over 45 percent relative humidity, but this figure increases if the air is colder. In other words, refrigeration machines are ineffective in an unheated location in a cold climate.
This dehumidification process uses a humidity-absorbing material called a desiccant, which is exposed to the air to be conditioned. The humidity-saturated material is then moved to a different location in the machine where it is "recharged" by removing the water absorbed from the air, typically by heating it. The desiccant is usually mounted on a belt or a rotating arm in order to move it within the machine.
Desiccant dehumidifiers are especially suited to lowering humidity at low temperatures. They are therefore effective for unheated locations in winter such as caravans, garages and outhouses or empty properties. These machines use more electrical power than the refrigeration type but do emit some heat as a by product of the process so raising the ambient temperature of the space being ‘dried’.
Features of Domestic Dehumidifiers
The advantage of a small portable model is you don’t need to have it fixed in one place. If a particular part of the house becomes too humid then you can move the dehumidifier to where the problem is.
Dehumidifiers have a tank to collect the water. The bigger the tank the less often you need to empty them. These tanks typically have a minimum capacity of 2 litres. They also normally have a warning light that indicates when the tank needs emptying and automatically switches the machine off once the tank is full.
Some machines have an alternative drain tube that enables the water to drain away rather than collecting in a tank. Remember that with a portable device it will not always be practical for it to drain externally, for example if temporarily located in the living room, hall or landing.
The drain tube works well, for example in a utility room, where you can insert the drain tube into the waste pipe used by the washing machine.
It is worth comparing how much electrical power each machine uses and estimating the relative running costs. Generally the desiccant machines use more power than the refrigeration machines.
Weight and Size
Weight and size is worth considering. Is there room for the machine and will you be able to manage to move it to other locations? A decent carrying handle is obviously another consideration when evaluating machines.
Also make sure there are electrical sockets available where you want to temporarily locate the machine. A smaller machine will typically weigh around 6 kg (13lb).
Find out how many litres of water a day the machine can extract. Typically, domestic machines will extract from 5 to 10 litres per day. Make sure the machine is suitable. Smaller models will handle a small flat and bigger machines can comfortably tackle a 4/5 bedroomed house.
Dehumidifiers are great for drying clothes. Some machines have a laundry mode designed specifically for clothes drying. This continually extracts moisture regardless of the relative humidity of the room.
If you want to run your dehumidifier using a time switch than make sure the model you use will auto start. In other words, as soon as power is applied it begins to extract moisture
Machines typically have more than one fan speed. Slower speeds are more economical and quieter but obviously the higher speeds will result in more rapid extraction taking place.