Essential Background Information on Dehumidifiers

Optimum humidity for human health and comfort

Humidity is the amount of water vapour in the air, and is measured in terms of Relative Humidity (RH), which is the amount of water vapour actually present compared to the moisture-carrying capacity of the air. The optimum RH for human health and comfort is approximately 50%, since higher levels promote mould, mildew, and dust mites, and lower levels can cause respiratory problems and encourage bacterial and viral growth.
Why not use air conditioners instead?

Air conditioners are primarily designed for temperature control rather than humidity control. They usually operate by means of a thermostat only (which senses room temperature) that allows the unit to maintain the desired temperature, and switches the unit off once it is achieved. The humidity may still be too high at this temperature, but the air conditioner is off and no longer extracting moisture. Furthermore, an air conditioner typically consumes significantly more energy than a dehumidifier for the same size space.
A dehumidifier with a higher power rating does not necessarily imply higher running costs

Regardless of the power consumption of a dehumidifier, its built-in humidistat will ensure that the dehumidifier is switched off once the desired level of humidity has been reached in a room. Larger, more powerful dehumidifiers will extract moisture from the air more quickly and operate for shorter periods. In fact, higher capacity dehumidifiers can often be more energy efficient. Since household humidity can vary greatly, it is advisable to purchase one or maybe two dehumidifiers that have a slightly higher capacity than required.
Keep doors and windows closed

One of the most important hints about dehumidification is to keep your windows and doors (especially external doors) closed, thereby reducing moisture ingress from the outside. A sealed room allows one to control the environment properly without interference from external factors.
Optimal placement of dehumidifiers

Dehumidifiers should ideally be placed such that the dry air discharge blows to the opposite end of the room. Since warm air rises, it is also better to place the unit closer to the ground. Most dehumidifiers can be wall-mounted, provided the recommended manufacturer clearances are adhered to, in order to ensure that there is sufficient air circulation around the unit. Observe all the manufacturer warnings regarding electrical safety – in particular do not set up water drainage near electrical circuits or devices.
Selection of dehumidifier based on climate

If you are using a dehumidifier in a warmer, more humid climate (typically above 20ºC) then a refrigeration type dehumidifier would normally work best, and for colder, drier environments (typically below 20ºC), a desiccant type dehumidifier is more effective (particularly if your damp problems occur mainly during winter).

Key features of dehumidifiers

  • Tank size / Continuous drainage
    The tank size is how much water the dehumidifier can store before it switches off. Dehumidifiers generally indicate this with a full tank warning light. To avoid emptying the tank too frequently, purchase a unit with a larger tank or use continuous drainage. Most dehumidifiers also provide the facility for continuous drainage by means of a pipe connection, sometimes including a condensate pump to extract the collected water to a convenient drainage point (e.g. it can pump upwards from a basement or wine cellar).
  • Moisture extraction rate
    This is the rate at which humidity is extracted from the air at a given relative humidity and temperature, typically expressed in terms of litres per 24 hours. Your requirements will depend on the room / house size and relative humidity levels. The manufacturer will often recommend room sizes along with their units. Also, consider Table 1 below for recommended extraction requirements sorted by space size and dampness conditions.
  • Humidistat
    Allows setting of comfortable humidity levels, saving energy by ensuring the dehumidifier only comes on when needed.
  • Efficiency
    The efficiency of a dehumidifier is typically measured in moisture extracted (litres) per unit of electricity used (kilowatt-hour). Also look for energy efficient features such as smart control, hydrophilic coated coils, intelligent defrost systems and rotary compressors.
  • Quiet operation
    There are dehumidifiers that are very quiet and suitable for use in bedrooms (e.g. the Delonghi DNC 65 at only 34 dBA).
  • Wall-mountable
    This allows one to place a dehumidifier out of the way against the wall. Almost all dehumidifiers can be wall-mounted with a suitable bracket, provided adequate clearances are adhered to as per the manufacturer specifications.
  • Portability
    Most domestic dehumidifiers are reasonably light and easy to move around. Desiccant dehumidifiers are usually lighter than their refrigerative counterparts. Units may have wheels or carry handles for easy mobility. Some larger units may require fixed installation. Continuous drainage will require a drainage pipe.
  • Additional features
    There are numerous additional features to look out for when purchasing a dehumidifier. The units we offer typically include many or all of these features. Built-in air purifiers & ionisers, Anti-frost, Auto-shut-off on full tank, Operational timer, Auto-start after power failure, Multispeed fan, Laundry mode for clothes drying, Drainage pump.


A Rough Guide to Required Moisture Extraction based on Area and Dampness

AreaMoisture Accumulation in litres per 24 hour day
Sq. MetersMild DampModerate DampDampWetVery Wet


*Mild Damp – Space feels mildly damp, increased risk for mould & dust mites, isolated damp problems, condensation droplets may appear.
*Moderately Damp – Space feels damp, condensation droplets may appear, has a musty odour only in humid weather.
*Damp – Space feels very damp and has a musty odour, especially in humid weather. Damp spots may appear on walls and floor.
*Wet – Space feels and smells wet. Walls or floor sweat, or seepage is present
*Very Wet – Walls sweat and floor is almost always wet.