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How to Choose a Dehumidifier

Using a dehumidifier can make a dramatic difference to your indoor environment and for anyone with allergies, eczema or asthma, controlling the relative humidity of the home or office has important health benefits. Anyone with arthritis or rheumatism can benefit from a drier home too. This is a guide to help you choose the right dehumidifier for your home or premises.

Types of dehumidifier

Compressor (refrigeration) dehumidifiers

A Compressor Dehumidifier works by drawing in air that passes over a filter and then over cold coils, much like those on a refrigerator. As the coils cool, the water condenses and drips into a collection bucket within the unit. The air is then reheated to room temperature and blown back out of the dehumidifier.

Compressor dehumidifiers have been around the longest and are still the most popular because they are reliable and energy efficient except at very low temperatures. They won’t work at all below 3˚C (38˚F) and perform poorly when the temperature is below 10˚C (50˚F) and humidity is also low. This only occurs in unheated properties. It is rare for a home with only partial heating to have a temperature as low as 10˚ C (50˚F).

Desiccant dehumidifiers

Desiccant Dehumidifiers tend to be smaller, lighter and can be quieter than compressor units. They are often used in premises where temperatures are less than 10˚C (50˚F ) or when a very low RH is required. Desiccants will extract moisture down to a humidity level as low as 10% whereas compressor dehumidifiers can’t get much below 40% RH, depending on temperature.

In an occcupied domestic environment Relative Humidity below 40% is not advisable for health reasons.

Desiccant dehumidifiers use a desiccant material, typically Zeolite, which absorbs water vapour from the air in a similar way to silica gel. A fan draws air into the dehumidifier and passes it through a section of a slowly rotating wheel holding the desiccant which dries the air.The moisture is extracted from the desiccant by heating a section of the wheel not being used to dry the air. All desiccant units are rated in test conditions of 60% humidity (as opposed to 80% for compressor units) and 30 degrees centigrade temperature.

They will extract the same amount of moisture irrespective of the temperature in which they are working and In a typical UK home a desiccant dehumidifier will use twice as much electricity to extract the same amount of water as a good compressor dehumidifier. Few desiccant dehumidifiers have humidistat settings, so they may take out more water than necessary and prove expensive. However there are no consumables on a desiccant unit - the desiccant material does not expire and will not need to be replaced / topped up.

The lifespan of a desiccant unit will tend to be longer than a compressor unit as it is a simpler process with fewer moving parts, no compressor and no refrigerant gas held under high pressure that can potentially fail

Thermo-electric and absorption

Compact, thermo-electric Peltier effect dehumidifiers are ideal for small spaces and usually remove up to 500ml moisture a day. They are quiet and lightweight so easdily portable as there is no compressor. They are often described as "Mini Dehumidifiers". Non-electric moisture absorbers are silent in use and work with a desiccant such as a layer of crystals that absorb the humidity through the top of the device and then filter it into a collection tub at the base.

The right choice

If you have an unoccupied property, boat or caravan or your property has a below average level of heating at all times, then a desiccant dehumidifier would be the right choice. They are good for:

  • Cellar drying
  • Document storage / archiving
  • Car / vehicle storage
  • Boat
  • Caravan
  • Motorhome

If you live in a home which has normal levels of heating throughout the day, then a compressor dehumidifier is by far the better choice. It will perform better, cost you significantly less to run and if you choose a large capacity model with automatic controls it will save you even more money and last much longer. They are good for:

  • Mould / damp prevention at home
  • Condensation reduction
  • Laundry / clothes drying

No moisture absorber or mini dehumidifier will ever be as powerful as an electric dehumidifier but they are popular and good in places where running a powered dehumidifier is impractical:

  • small spaces
  • cars
  • cupboards
  • wardrobes

Low purchase price or low running cost?

When choosing the best dehumidifier to protect your home from condensation and dampness you need to consider the total long term cost not just the purchase price.

The cost of electricity consumed is an important consideration. Dehumidifiers with ordinary humidistats are inefficient and costly to run. A large capacity dehumidifier with an ordinary humidistat will need to adjusted several times a day or it will run unnecessarily wasting electricity.

Dehumidifiers with intelligent control technology are up to 50% more efficient saving between £30 and £55 every year. The compressor Dehumidifiers from Ebac have this feature, known as ‘Smart Control’, as has the Banamite Dehumidifier with its ‘Set & Forget’ automatic controls. Choosing a dehumidifier with a larger capacity than you need will also save money in the longer term because it will need to run less often than a lower capacity dehumidifier. This means it’ll last longer too.

How warm and busy is your home?

Another important factor is how you heat your home. For example if you heat every room in your home 24 hours every day, you probably won’t need a dehumidifier at all. However this is a very expensive solution and most people only heat their homes for part of the day and some rooms are never heated at all.

Another factor is the amount of moisture you put in to the air. As we breathe, we add moisture to the air and very day activities such as having a bath/shower, boiling water for cooking, and even drying our laundry also adds moisture to the air. The humidity level in your home is also therefore affected by the number of people in it.

For example, 2 people in a 5 bedroom house will need to remove less moisture than 2 people in a 2 bedroom house, because the bigger house has more capacity to hold the moisture.

How much water do you need to remove?

The amount of water you need to remove is determined by several factors. How many people live in the house, your daily routines and the type of house you live in. Bungalows, for instance, are more prone to condensation and dampness than 2 storey houses.

Homes where there are unheated rooms or the heating isn’t on for 24 hours each day are also more prone to condensation and dampness.

Summary

Because it doesn't make economic sense to heat every room in your home for every hour of every day and because there are so many other variables, the best advice is to buy a dehumidifier with a high capacity and make sure it has an intelligent automatic control system such as Ebac’s patented Smart Control or Banamite’s Set & Forget.

For tackling damp and mould in cupboaards and small spaces or for clearing condensation and musty smells from unoccupied and unheated boats, caravans and holiday homes, a desiccant dehumidifier or a granular adsorption block will do the trick. Mini dehumidifiers that use Peltier thermo-electric technology are particularly effective here too.

Guide to recommended models:

up to 500ml extraction.Small spaces, cupboards:

12 litre Extraction, Empty premises, 1-2 person homes

18 litres Extraction, 1-5 people:

21-25 litres Extraction, any number of people:

 
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