Whole House Dehumidifier



In some ways a whole house dehumidifier is exactly the same as any other dehumidifier. It does the same job and it works the same way to control the moisture content of the air.


The big differences are the scale and construction of the area, the whole house, in which you wish to control humidity.


Let's be clear from the outset, if your problem is located in one area of the house, one storey of the building, a single room or two adjoining rooms for example, you almost certainly do not need a whole house dehumidifier. If your home is very compact you may not need one either.


We stress this point because whole house dehumidifiers have a large capacity, cost more to run and, usually, more to buy than less powerful machines designed for smaller areas.


Manufacturers' specifications will indicate the size of the area which each model should dehumidify. While we consistently recommend that you should aim to buy "one size bigger" than you need to allow a safety margin; we do not encourage "over-kill" which will cost you more than is necessary.


So, if your room area is 600 square feet a machine rated for 1000 square feet will be fine. If it's 900 square feet a model rated for 1500 will usually be the wiser choice, but you do not need a whole house dehumidifier rated for 5,000 square feet!




So, you have a family sized home and you have a problem with humidity, possibly damp, throughout the house. What kind of problem is it?

High Ambient Humidity


In certain areas the climate is very warm, with high relative humidity, in some or all seasons. This can make everyday living uncomfortable. The air temperature alone can cause discomfort but the high humidity makes it feel even warmer. This is because water cannot evaporate quickly into air with a high relative humidity.
In warm conditions we sweat, the liquid water evaporates from our skin and takes heat with it, thus cooling our bodies. If the sweat cannot evaporate as quickly as it should we cool more slowly; we not only feel hotter, we are hotter.


If we have air conditioning this not only cools the air but also dehumidifies it, lowers the amount of water vapour in it. There are two limitations in this process. First, the air conditioning switches off when it reaches our chosen temperature, not our preferred humidity level; second, the relative humidity of the air does not fall as much as the temperature because cooler air "holds" less water than warmer air. In fact if the air conditioning did not remove water the relative humidity would actually rise.


In addition, if the temperature is low enough for the air conditioning to be switched off there is no dehumidifying effect at all, even when relative humidity is uncomfortably high.


For this reason a separate, whole house dehumidifier is frequently installed to complement the air conditioning, controlling relative humidity independently of the air temperature.


For this purpose many people with air conditioning choose a whole house dehumidifier which makes use of the ducting installed for the air conditioning system. The advantages are that the unit can be placed out of sight, in the least inconvenient place, and where the noise of the compressor will not be a nuisance, a basement for example.


While it is possible for a competent house-holder to undertake the installation we recommend that a qualified HVAC (Heating, Ventilation and Air-Conditioning) engineer is employed to do the work.


For those who do not have the appropriate ducting in place the least expensive solution is use a high capacity, free-standing dehumidifier, powerful enough to cope with the total floor area of the house.


This brings into focus the other difference we referred to, the construction of the house. Most houses are divided into rooms, enclosed by walls, with doors. For a free-standing whole house dehumidifier to work effectively all doors must be open and a free flow of air enabled to move about the building. It goes without saying that in conditions of high ambient relative humidity all windows must remain closed.


Regrettably this is a second best solution. The bigger the house the less effective it is likely to be, particularly where the architecture of the building, number of storeys, width and height of corridors and stairways etc., does not make the free flow of air easy.


In a larger home, or one with unhelpful design features, two or more dehumidifiers may be the preferred solution. The disadvantages are the inconvenience of free-standing units in living areas and the energy costs; usually a single dehumidifier designed for whole house use will use less electricity than several smaller ones. The advantage is that high capacity free- standing units can cost considerably less to buy than the integrated machines, even where more than one is purchased.


A Temporary Damp Problem


Sometimes we are unlucky enough to have a sudden flood in the house, burst pipes for example, and need to dry it out. Once the mops and buckets have been put away there will still be large amounts of water locked in the fabric of the house that would take far to long to dry out naturally.


If your house insurance covers you against the accident your insurance provider will usually take care of the restoration expenses, including the rental costs of one or more high capacity dehumidifiers. If this is not the case you may consider hiring these machines at your own expense.


If you do decide to hire one or more dehumidifiers it is important to select those which will deal with the largest amount of water in the shortest period of time. Rental charges can be relatively high and the shorter time you use the dehumidifier(s) the better. In some circumstances it may be less expensive to buy rather than rent if you select a high capacity machine at a modest price. If you do not have a long term need for the machine you will not need the most durable, and therefore most expensive brand.


It is impossible to recommend a course of action as individual circumstances differ. We can only suggest you do the math before you make your choice.


Permanent Damp Problem


If your home suffers from chronic damp, especially in the colder and wetter seasons, a whole house dehumidifier may be for you.


Please ensure, before making the investment, that you have eliminated every curable reason for the damp. A leaking roof is fairly obvious but other causes are not always so easy to spot.


Once you have eliminated the possible faults and corrected them you have either solved the problem or you have one of two problems remaining. Either, you have a problem to correct which is so expensive it would not be worth the cost, such as re-building the house, or you have a genuine problem of chronic damp and don't wish, or can't afford to abandon your home.


In these cases a whole house dehumidifier would be advisable. The options are the same, therefore, as for the person whose problem is high ambient humidity, an integrated dehumidifier or one or more free-standing ones.




General Points


Whatever solution you choose, whatever your reasons for choosing, there are some points to consider when selecting your dehumidifier.


  • It is a high capacity device, it must have a continuous drain facility or you will be emptying the bucket a dozen times a day.

  • It uses a higher amount of power than a smaller dehumidifier so, for the sake of economy, it should have a humidistat so that it does not operate once the desired level of relative humidity has been reached.

  • If it has to operate in a low temperature environment, say a basement, it must function at the lowest temperature it is likely to encounter. If it is a refrigerant dehumidifier it needs, therefore, hot gas defrost. A dehumidifier using desiccant technology will not be affected by temperature but will use more electric power.

  • If you are likely to be away from home for periods of days or weeks, or the dehumidifier is not readily accessible, it needs automatic restart so that it will resume operation, at your chosen settings following any interruption to your power supply.


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