Many homes and buildings suffer from high humidity and the problems it causes; Damp patches, condensation on walls and windows, mould and increased dust mite populations. A good domestic or commercial dehumidifier will reduce the levels of moisture and help to alleviate these problems.

High humidity is a problem that affects many environments. From homes to building sites, wine cellars to swimming pools.

Newer homes are better sealed with double glazing and often have less ventilation; older homes may have solid walls that allow damp to enter into the home. Common causes of excess moisture are drying clothes inside and poor ventilation

A domestic or commercial dehumidifier from Kroll is an ideal solution for so many applications;-

  • Drying out water or flood damaged buildings, eliminating the need to replace and reconstruct
  • Developing stable environments for exposed metal to prevent corrosion
  • Reducing drying times at construction sites for concrete, insulation, and fireproofing
  • Preparing surfaces and vessels for painting and coating applications
  • Blanketing equipment to protect from humid air
  • Maintaining correct ambient conditions for laying of flooring
  • Prevention of mould and fungus growth

Domestic or Commercial Dehumidifier

So, what is 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.


Performance of dehumidifiers? How are they calculated?

Most dehumidifier manufacturers quote the capacities of their dehumidifiers based on a temperature of 30°C and 100 % relative humidity i.e the temperatures and humidity levels that you would find in Florida, in the summer. The capacity the units will extract is given in litres per 24 hours. If the temperature is lower, as we often find in the UK, then the performance of the unit is lower. Here is an example;-

                                                                                                          Kroll unit                                                       Kroll unit

Temperature & Relative Humidity                        T20D dual voltage  model                       T40D dual voltage model

At 10°C / 60% Relative Humidity                                                       4.2 litres                                                                 8 litres

At 25°C / 60% Relative Humidity                                                       9.5 litres                                                                 20 litres

At 30°C / 60% Relative Humidity                                                       20 litres                                                                  36 litres

As you can see from the above, the colder the temperature, the less water is extracted. At a temperature of 5°C refrigerant dehumidifiers will stop extracting all together


Domestic or Commercial Dehumidifier

What can I do about this, to get my extraction rate up ?

Quite simple, add a heat source to the area to be dried. The best option is an electrical heater or an indirect ( this means the products of combustion do not enter the area being heated ) oil or gas heater. The hotter the area is, the better the extraction rate you will achieve

Airflow is important – You need to ensure that you are using the right size dehumidifier for the area you want to extract the vapour from. The general rule is –

To keep the room dry, multiply the air volume the unit will do by 2

So, for the Kroll T20D it is 160 M³/h thus a room with a volume of 320 M³

To dry a room, multiply the air volume the unit will do by 1

So,  for the Kroll T20D it is 160 M³/h thus a room with a volume of 160 M³

Here’s a quick reference chart for all our models




Room Volume for

Keeping Dry  / m³

Room Volume for Drying  / m³


What can happen if I put 2 smaller dehumidifiers in one room, for example I want to keep dry a 640 M³ building, with two Kroll T20D dehumidifiers?

This isn’t a problem, although you need to evenly place the units within the area, for even extraction to take place. If one side of the room is wetter than the other, expect to see the closest dehumidifier to have extracted more than the other unit.


I’ve just had a phone call from a customer and he says the unit isn’t working, nothing or very little is water is coming out?

We test every domestic or commercial dehumidifier prior to dispatch – the unit is working, if the green light is on – simple as that

It’s probably one of these reasons, why the the performance is poor

  1. Our Domestic or Commercial Dehumidifier units only work down to 30% Relative humidity – the ideal relative humidity is around 50% or less within a living environment –  check what relative humidity you have with a hydrostat. If it’s under 30% the unit won’t work
  2. What’s the temperature within the room? Is there heating within that area? Please bear in mind night time temperatures, where heating systems have be turned off, a room can easily get down to 5°C in the winter – the unit won’t work at 5°C or below , and the performance drops off dramatically with lower temperatures, as stated previously
  3. Do you have windows / doors etc open that is allowing fresh damp air into the area?
  4. Are you using a direct fired oil or gas heater? if so , then this adds water content, that is given off in the combustion process
  5. Is the unit the correct size for the room – please see the above sizing chart
  6. Do you have more than one domestic or commercial d dehumidifier in the room – are they evenly placed? Is one in the in the wetter area?

Domestic or Commercial Dehumidifier


For more information on our domestic and commercial dehumidifier range, please click on our main products page here .  Alternatively, please give us a call on 01202 822222 and our dedicated sales team will be happy to offer advice and assistance or just contact us by mail by clicking here