FAQ's: Choosing the right dehumidifier Frequently Asked Questions regarding choosing the right dehumidifier. General   1/ How do I stop mould from growing or mildew from forming?   Mould will not grown in humidity below 60% RH (Relative Humidity). By running a dehumidifier set to maintain humidity at 55% or lower, mould will not grow.   2/ Why am I only getting a lot of condensation / damp appearing in certain rooms?   Moisture condenses on the coldest surfaces: therefore although the humidity level may be high throughout your property, it will tend to condense on cold surfaces, typically windows, or on the walls in rooms that are either north facing, east facing, rarely used unheated rooms, or rooms that are the only ones to have external walls.   3/ How long do I need to leave my dehumidifier running?   If your dehumidifier has a humidistat on it (most of them do) ideally set the humidity level and leave the unit running – it will cut in and cut out as it needs to in order to maintain the desired humidity. Alternatively, through a little bit of trial and error, you may prefer to switch your machine on and off as required or run it on the timer if it has one.   4/ Are dehumidifiers expensive to run?   Most domestic dehumidifiers will consume between 180 watts and 660 watts per hour – this equates to between 2 pence and 7 pence per hour at 2012 domestic energy prices. Bear in mind that the drier the air, the quicker the air will warm up when your heating is on. Therefore during the winter months the running cost of your dehumidifier will tend to be more than offset by the saving on your heating bill.   Used correctly, dehumidifiers can be a much more economical option for clothes drying than a tumble dryer. Even the latest energy efficient tumble dryers use at least 2500 watts per 120 minute cycle compared to an average of 880 watts for a desiccant dehumidifier for the same amount of time. Consider that a desiccant dehumidifier positioned next to or below a clothes maiden will not only draw the moisture from the clothes but also blow warm, dry air over your clothes, drying them quickly – and there is no chance of your clothes being damaged in the process!     5/ Where is the best place to position my dehumidifier?   Although a build up of moisture, condensation or damp (due to high humidity) may be more apparent in certain rooms (see Point 2 above), the cause of the humidity will normally be routed in other rooms: eg drying washing, running showers and baths, boiling kettles and pans of water when cooking etc. Therefore it is best to try and position your dehumidifier at a mid point in your property for the most part. Some people like to move their unit as and when required – eg if drying laundry in one room or if there is one room that is suffering the worst from condensation / damp.   6/ What are the pros and cons of a desiccant dehumidifier over a compressor dehumidifier?   Desiccant units are smaller, lighter, quieter, more robust and, in a real world scenario, much more effective and efficient at extracting moisture. Therefore in real terms desiccant units tend to be cheaper to run. We tested a 7 litre desiccant against a 20 litre compressor in a domestic environment around 19 degrees centigrade temperature and the desiccant removed almost five times the amount of moisture in the same period of time. We would only really recommend you use a compressor unit in temperatures of 20 degrees centigrade or higher.   7/ Does the desiccant material in desiccant dehumidifiers need to be topped up / replaced?   No – the desiccant material does not expire and does not need to be topped up or replaced: 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 which holds desiccant which dries the air. The moisture is extracted from the desiccant by heating a portion of the wheel not being used to dry the air. At this point the moisture immediately drips out of the Zeolite and the process starts again.   Domestic: General Flat / House   1/ What size unit do I need for my two bed flat / apartment?   Answer: 7 litre desiccant / 10 – 12 litre compressor   2/ What size unit do I need for my 2-3 bed house?   Answer: 7 litre desiccant / 12 litre compressor   3/ What size unit do I need for my 4-5 bed house?   Answer: 7 - 10 litre desiccant / 20 litre compressor   4/ What size unit do I need for my 5(+) bed house?   Answer: 10 litre desiccant / 20 litre compressor   5/ What size unit do I need for my 2-3 bed bungalow?   Answer: 7 litre desiccant / 12 litre compressor   6/ What size unit do I need for my 4-5 bed bungalow?   Answer: 10 litre desiccant / 20 litre compressor   Domestic: Laundry Drying   Q: What is the best unit for drying laundry?   Answer: If you dry your laundry in a very warm room then a powerful 20 litre compressor unit will be suitable. If you dry laundry in your kitchen, living room or spare bedroom then a desiccant unit will be a much better choice. Some desiccant units have a laundry function on them and remember that a desiccant unit will be blowing warm, dry air over your laundry as well as sucking the moisture out of your laundry.   Domestic: Cellar   Q: What is the best unit for a cellar?   Answer: Cellars tend to be quite cold therefore a desiccant unit is best as they extract moisture at a constant irrespective of temperature whereas compressor dehumidifiers only work well in warm (20+ degrees centigrade) temperatures. Desiccant units are designed to run unattended for long periods of time in remote areas. They are supplied with a continuous drain option, as well as being able to collect in the tank, and are fitted with auto restart which means they do not need to be reset after a power cut, and can be left running on a plug timer if desired.   Domestic: Garage   Q: What is the best unit for a garage?   Answer: Garages tend to be unheated therefore a desiccant unit is best as they extract moisture at a constant irrespective of temperature whereas compressor dehumidifiers only work well in warm (20+ degrees centigrade) temperatures. Furthermore, a desiccant can reduce humidity to as low as 40% which is below the rusting point of metal – making them ideal for storing machinery or tools. Desiccant units are designed to run unattended for long periods of time in remote areas. They are supplied with a continuous drain option, as well as being able to collect in the tank, and are fitted with auto restart which means they do not need to be reset after a power cut, and can be left running on a plug timer if desired.   Leisure   Q: What is the best unit for use in a motorhome / caravan?   Answer: desiccant unit rated at around 7 litres per day will be best as is it will work as well in cool conditions as well as warm. Desiccant units are designed to run unattended for long periods of time in remote areas. They are supplied with a continuous drain option, as well as being able to collect in the tank, and are fitted with auto restart which means they do not need to be reset after a power cut, and can be left running on a plug timer if desired.   Q: What is the best unit for use on a boat?   Answer: desiccant unit rated at around 7 litres per day will be best as is it will work as well in cool conditions as well as warm. Desiccant units are designed to run unattended for long periods of time in remote areas. They are supplied with a continuous drain option, as well as being able to collect in the tank, and are fitted with auto restart which means they do not need to be reset after a power cut, and can be left running on a plug timer if desired.