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Dehumidifier Frequently Asked Questions

1. What does a dehumidifier do?
A dehumidifier removes water from the air in your home until relative humidity is reduced to the level you choose. Once it has reached this level a good dehumidifier should  automatically maintain that comfortable level with no interference from you!

2. What is relative humidity?
Relative humidity is a measure of how much water is in the air relative to the amount that air could hold if it was saturated. Relative humidity is expressed as a percentage. When relative humidity reaches 100% it is at the "dew point". In other words the air is "full" of water and that water will start to condense onto any surface. Warm air holds more water than cool air so as air cools relative humidity rises even though the physical quantity remains constant.
For every fall in temperature of 20°F/10°C the capacity of the air to hold water is halved. For example air at 80°F with a relative humidity of 50% will reach the dew point, 100% RH when it has cooled to 60°F.

3. Where does the water come from?
Water is always in the air, inside and outside the home. The amount inside the home varies and is increased by many routine daily life activities such as cooking, washing, showering, making tea and breathing. If you have uncovered water containers in the home like fish tanks etc, then these will also add to the amount of water in the air.

4. What is the ideal humidity level for my home?
Generally a relative humidity of 50% is comfortable for your home. This will protect your home and belongings, prevent mold growth and control the dust mite population. There is no real need to reduce humidity below the 45-50% mark. To do so will simply cost more in energy while serving no useful purpose.

5. How does a dehumidifier work?
Most dehumidifiers work by drawing air from the room over a coil cooled to a very low temperature by a refrigeration system. These are commonly known as refrigeration dehumidifiers . The water vapor condenses on the cold surface and the liquid water drips into the water collection bucket underneath.  More and more dehumidifiers are now using an alternative method known as desiccant dehumidifiers. The desiccant dehumidifiers pass the air over a wheel coated with a water absorbing material ( called desiccant).  The water is removed from the desiccant by passing a stream of warm air through it whereby it is dried and re-generated to collect more moisture on its next pass. The collected water is collected in the units water collection tank.

6. How long will it take to get the moisture under control?
As long as the dehumidifier you choose is large enough for the area it is working in, and there are no specific damp problems,  then a dehumidifier will normally reduce the humidity to the chosen level within a few days to a week. This timescale does not apply if the room has been flooded, in which case one or more dehumidifiers will be needed and possibly supplemented by air movers and other specialist equipment. This work is usually undertaken by specialised water damage specialists.

7. How much water does a dehumidifier remove?
The answer to this depends on three specific factors. The power of the dehumidifier, the room temperature and also the relative humidity of the air in that room. A 12 litre dehumidifier will rarely,  if ever,  remove 12 litres in a single 24 hour period. Once relative humidity has been reduced to your chosen level the dehumidifier should only be operating intermittently to maintain that level so the amount of water collected in the bucket will be lower still.

As a general rule of thumb you may need to empty your dehumidifiers  bucket at intervals ranging from once every two days to twice a day, depending on the conditions. It is only in exceptional circumstamces that a properly sized dehumidifier will need emptying more frequently than this, unless of course you have placed it in a very damp room for the first time.

8. Can I use the water that collects in the bucket?
The water collected in the dehumidifiers tank is called condensate, you can use this in your iron or to water the plants! However, it should not be drunk by humans or animals as it may contain traces of substances that could make you, your pets ill.

9. How do I know how big a dehumidifier I need?
This is basically down to the size of the room and how wet it is. But in general you will find most dehumidifiers on our site are classed by house size to make the job easier for you to choose. For instance our smallest dehumidifiers are ideal for anything up to a 3 bedroom house. Our larger units are ideal for homes with up to 5 bedrooms. In general terms we would always recommend that you err on the side of caution and if in any doubt buy a dehumidifier a size larger than you may appear to need. Larger dehumidifiers remove more water per energy pound spent and run for fewer hours in a given space than smaller ones. The energy saving will almost certainly be greater than the difference in purchase price.

10. How does a dehumidifier prevent mold and mildew?
A dehumidifier prevents mould and mildew growth in two ways. First it dries out the room, drawing damp from the contents and fabric of the room on which mould and mildew will inevitably form and prevents that damp from recurring. Secondly, providing the dehumidifier is set to maintain relative humidity at 50% or slightly below, the air is too dry for mold and mildew spores to develop. Fungi need airborne water as well as surface water to grow!

11. Where is the best place to site my dehumidifier?
In an ideal world a dehumidifier would be silent and invisible. The next best thing is to be out of sight and earshot. Unfortunately the first is impossible and the second, while achievable in some cases, be more expensive in cost and effort. If you need to lower humidity throughout your house a whole-house dehumidifier is the best option. It is easy to fit, virtually silent and is the cheapest solution for whole house control. If you are using a portable dehumidifier in a small to medium sized room, a laundry room or a bedroom for example, it is not particularly important where you position it.

12. What is Continuous Drainage?
All portable dehumidifiers have a water collection container, often called a tank or a bucket,  to collect the water extracted from the air. These buckets are quite small, to keep the overall size of the dehumidifier down, and need to be emptied at least once a day. Because it may not be convenient, or possible, to empty the bucket daily almost all portable dehumidifiers for home use are designed to allow the water to be drained directly as it is collected. This is known as continuous drainage.  In the casing of the dehumidifier a small hole has been cut to allow a small hose ( most of our units come with this hose in the box ) to be attached to the dehumidifier through which the water can be drained. The water is drained by gravity alone so for effective continuous drainage the dehumidifier needs to be raised a foot or two above the floor and the hose run to a floor level drain.

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