Dehumidifier FAQs

Dehumidifier FAQs

What is a Dehumidifier?

A dehumidifier is a product designed to manage room or process humidity levels to prevent signs of damp occurring.

How does a dehumidifier work?

A dehumidifier extracts excess moisture out of the air. Dehumidifiers are designed to prevent condensation, and dampness in a wide variety of applications such as clothes, houses, classic car storage, furniture storage, hair salons, cafes, restaurants, caravans or boats, cellars or even production processes or machinery. There are two different types of dehumidifiers available, the more popular type is the compressor-driven refrigerant dehumidifier. This style of unit functions by drawing air across two sets of coils containing refrigerant one being cold and the other being hot stripping out all the moisture before draining water into a storage tank, container or pumping to a suitable drainage point. The Desiccant is the less common version available and this style of system uses a special material that absorbs moisture out of the air before releasing captured water into a container or exhaust damp vapour to a suitable outdoor area.

Can I leave the dehumidifier running at night?

Yes, we recommend using a dehumidifier 24hrs, however, be aware that there will always be a noise generated from the machine when it is operating. We suggest selecting one of our smaller and quieter Woods dehumidifiers for example the MRD10, MRD14, or Woods 36 if they are to be used near bedrooms. Otherwise, we suggest using the dehumidifier from early morning until late evening and then turning the machine off. If the machine is in a hall and bedrooms are upstairs then you may not even hear the machine.

Do I need to leave the heating on when operating my dehumidifier?

The warmer the air the easier it is to extract moisture.

Do I have to leave the dehumidifier running constantly?

All dehumidifiers are fitted with a humidistat that controls the operation of the machine. When the humidity level is satisfied, the dehumidifier will switch off though some machines allow the circulation fan to continue after the dehumidification process has stopped. Sometimes the fan running function can be beneficial to maintain circulation.

What are the running costs of a dehumidifier?

It costs around thirty-four (34) pence per hour for 1kW of electricity. (Energy rates based on UK average costings in October 2022) On each product, we display the wattage so therefore a 300w machine will cost around eleven to twelve (11-12) pence per hour depending on what you pay for your electricity. With an average dehumidifier, it will cost around eleven to twelve (11-12) pence per hour if running continuously. Desiccant adsorption machines will have a higher running cost starting around twenty-seven (27) pence per hour for DD200 model rising with larger models due to inbuilt heater to assist moisture extraction performance operation at lower temperatures. However, the adsorption machines such as DD200, DD300 & DD400 will do the job quicker at temperatures below 20 deg C and therefore overall costs may be less than with a conventional refrigeration dehumidifier. Running costs can increase significantly on the larger desiccant dehumidifier range.

Once the house is brought under control the actual running costs will reduce significantly, as the dehumidifier will need to operate less.

Do all CAS-Hire dehumidifier hire ranges have a humidity control?

Not all of our CAS-Hire dehumidifier hire fleet offers variable humidity control. A large percentage of the industrial heavy-duty models simply have an on / off setting however the smaller units have inbuilt humidistat’s.

Is room size important when choosing a dehumidifier?

Yes and no. What is most important is the amount of water you need to take out of the air. The more water in the air, the larger the capacity you will need. A small room with a lot of moisture may need as much dehumidification as a large room with average moisture content. When in doubt, it’s always better to oversize a dehumidifier. Dehumidifiers extract moisture out of the whole volumetric area of the room and not simply the specific patch.

Where should I position the dehumidifier?

Position the dehumidifier centrally in the affected area.

Do dehumidifiers raise the heat in my house?

Yes, but this can be either good or bad. The warmer the room, the easier and more efficiently you can remove moisture so the machine will have to work less. Depending on the size of the room, you could raise the temperature by 5-10 degrees.

Are dehumidifiers portable?

Generally yes all of our dehumidifier hire ranges have either carrying handle castors or rear wheels.

The specifications indicate that a dehumidifier can extract 20 litres per day yet the water container only holds 4 litres?

Maximum extraction rates are based on temperatures of either 32 deg C & 90% RH or 30 deg C & 80% RH (Relative humidity). It would say within the UK it’s reasonable to expect a maximum of around 10 or 25 litres per day as the extract rates decrease with a drop in temperature.

Does it filter the air?

All machines have an air filter mainly to protect the machine. If you especially want clean air then please look at our air cleaner hire range on our website

I have a second home. What happens if we have a power failure, will the machine turn itself back on?

That depends on the brand and model that you hire. Most dehumidifiers with manual humidistat controls will turn themselves back on. With the electronic controls, it varies. Our Woods dehumidifiers will turn back on and will continue to remove moisture at the humidity level for which you had set the machine. Some of the Building dryer industrial dehumidifiers will not turn back on and require having the “power on” button pushed to restart.

The dehumidifier I hired runs all the time – why?

The dehumidifier that you hired is probably not capable of removing the amount of moisture in this area. If your area needs to have 50 litres of moisture removed from it daily and you have a 40-litre unit, you will never catch up and the machine will run continuously.

Can a dehumidifier cover multiple connected rooms?

That depends on the total area of all the rooms, the layout of the rooms, and the circulation space between the rooms. The more open the rooms are to each other (not 3ft doorways), the easier it is. Having fans in the rooms to move the air would certainly help move the air towards the main area where you have placed the dehumidifier.

How much noise do they make?

Each make and model may differ in sound levels that are measured in (dBA). The higher the (dBA) the higher the sound level. Noise levels, particularly in the larger dehumidifiers, can increase especially when considering use in domestic applications.

Can I have a permanent drain fitted?

Yes, permanent drain kits are available for both the Ebac and Woods dehumidifier range. The Woods 40 dehumidifiers come complete with a drain hose and inbuilt pump.

How does the permanent drain work?

The hose connects to a drain point on the dehumidifier and the hose outlet must be lower than the dehumidifier drain point as it is a gravity drain only. (The Woods 40 and a couple of the Ebac models have inbuilt water pumps and can pump water up to 2.5m above the height of the dehumidifier and up to 10m in distance)

What if the hose becomes blocked or kinked?

You should periodically ensure that the drain hose is clear to prevent water back up or pump burnout.

I still have condensation on windows though my dehumidifier has stopped – why?

Either you have the moisture extraction setting on the dehumidifier too low or the dehumidifier is undersized. While a relative humidity (RH) level of 50% may be ideal for domestic use, you may have to increase the setting levels in periods of colder weather and make your dehumidifier work harder. In larger premises, you may need more than one dehumidifier

How long will it take to get my condensation under control?

This depends on the level of the problem. Generally, you will see an improvement within a few days but do allow 1- 2 weeks to get the problem under control.

Does a dehumidifier tell me my exact humidity level?

Some models offer digital control however we recommend purchasing a Thermo-hygrometer so you can measure relative humidity and compare it with the setting on your dehumidifier.

What causes condensation?

In Britain, condensation in houses is mainly a winter problem particularly where warm moist air is generated in living areas and then penetrates to the colder parts of the building. The moisture in the air comes from a number of sources within the house. Water vapour is produced in relatively large quantities from normal day to day activities – a 5 person household puts about 10 kg of water into the air every day (without taking into account any heating) – i.e. – Breathing (asleep) 0.3 kg – breathing (awake) 0.85 kg – cooking 3 kg – personal washing 1.0 kg – washing and drying clothes 5.5 kg – heating – especially paraffin and flueless gas heaters. For every litre of paraffin burnt over one litre of moisture vaporizes into the air. Every carbon fuel produces some amount of water from combustion. (1 kg of water equates to about 1 litre) Moisture can also be drawn from the structure of the building into the internal air; from below the floor or through the walls/ceilings.

I have mould & mildew so will a dehumidifier get rid of this?

Yes, a dehumidifier will help prevent further problems but you must use a mould spore remover to actually kill the spores.

What is the difference between a dehumidifier with a compressor and one without?

Traditionally dehumidifiers worked on the refrigeration principle where air passed over a cold refrigerated coil and moisture condensed on the coil and drained into a container. The compressor less adsorbent desiccant dehumidifiers such as DD hire range work on the principle of moist air being drawn into an absorber that is a slowly rotating disc impregnated with silica. A heating element applies heat to the absorber that heats the moisture to a high-temperature vapour that is immediately released from the absorber and condenses into water that falls into the collection tank. An absorption dehumidifier is more efficient at colder internal temperatures and can often be quieter.

Do I need to change or replace the Silica on any of our desiccant dehumidifier hire ranges?

No, there is nothing to replace

Can I dry clothes with a dehumidifier?

Yes, you can. Ideally, place your clothes on a drying rack and place the dehumidifier in the same room and leave it in a continuous or laundry setting. Shut the door to that area and the dehumidifier will take in all moisture.

Will just one dehumidifier be sufficient for my home?

Normally one will be sufficient but in the case of large houses or where you may have several floors then more than one may be required.

Which dehumidifier do I need for my garage?

Garages are generally unheated so consider the desiccant dehumidifier hire range as they operate in low temperatures without losing extraction capacity. Large car garages may require more than one machine. Other large storage areas, warehouses etc should consider commercial dehumidifiers.

What is the ideal humidity level for my home?

Between 40 and 60% so the ideal would be 50%.

Why does my dehumidifier freeze up?

The coils of refrigerated dehumidifiers will ice up but a sensor or timer will stop the compressor and allow the ice to melt either by circulation ambient air or using a method called hot gas defrost that reverses the refrigerant flow to force hot refrigerant vapour through the coil and so the ice melts quickly and the machine starts again much quicker. Icing up to a certain extent is normal but severe icing up can be due to a shortage of refrigerant, insufficient airflow or a malfunction.

Do all dehumidifiers have a water container?

Yes, all domestic dehumidifiers have or require a container that ranges from 3.5 litres to 15 litres capacity.

Will the dehumidifier switch off when the tank is full?

No, only the Woods 36 have tanks are fitted with a float switch so once full they will shut off the compressor or in the case of Desiccant dehumidifier the heater element will shut off.

When will delivery be?

If you order prior to 3 pm on any working day you will receive the machine the following working day. However, deliveries to the Highland & Islands or to Northern Ireland may take 2/3 days. An AM or Saturday delivery is available at extra cost.

Saturday Delivery?

We can arrange delivery on a Saturday for an additional cost of however we do not offer a Saturday collection service.

Do I need to be in to receive the dehumidifier?

Preferably however it’s not essential, as long as you notify us of a neighbour or alternative suitable address where someone can sign for a unit on your behalf. We also recommend all goods be signed as unchecked just in case anything has been accidentally damaged in transit. We can also arrange delivery to your workplace if that is more convenient for you.