This is a very common question, when working out the actual cost of running a dehumidifier a lot of people start to look at other benefits from the running cost, such as the heat produced by the dehumidifier, and what, if any, effect it will have on the room temperature.
First of all, there are two types of dehumidifier technology, one is referred to as a rotary design and uses a compressor similar to a fridge, the other is a type which uses desiccant gel particles (similar to the little packets you get in packaging), the desiccant removes the moisture from the air, and water is then extracted by heating the desiccant over a small heating element.
A damp room will always feel colder due to the high humidity level, and its effect on skin temperature, and so removing the moisture with either of the dehumidifier types will, effectively, make the room ‘feel’ warmer and more pleasant without actually raising the room temperature itself. However if you are looking for a dehumidifier which not only removes moisture but will justify a percentage of its own running costs, through raising the actual room temperature, then only one of the two available dehumidifier types will be suitable.
If room heating is a requirement of your choice of dehumidifier then you shouldn’t consider the rotary compressor type, as these do not heat the air, they work simply by removing moisture by passing the air over cooled coils, so that it condenses back to water and although they will still make the room more comfortable by lowering the humidity level, they will not return any warmed air into the room, and so although this design is still effective at reducing damp, the heating effect will be non existent.
The best choice for removing damp and also increasing the room temperature, will be the Desiccant Dehumidifier. Because these have a built in heating element to regenerate the desiccant gel, the heat produced through normal operation is not lost or entirely absorbed into the gel, and so all of the heat is blown into the room by the powerful fan, so not only does it remove moisture from the air, it heats it as well before sending it back into the room. I have personally tested several of the dehumidifiers on the market, and the temperature of the air being blown from the dehumidifier ranges from 7c to 12c higher than the ambient temperature of the room air that is being sucked in, which over several hours of normal use, is effective at raising the room temperature by a similar margin.
It is worth pointing out however, that during very cold periods, a dehumidifier alone, may not be enough to make the room warm enough to sit in for long periods of time, and therefore a dehumidifier shouldn’t be considered to be a primary or sole source of heating for a given room. However what the dehumidifier will do, in addition to removing damp problems and lowering humidity is to create a very good and effective source of background heating, warming the room by several degrees and therefore reducing the amount of heat required from other forms of heating, therefore reducing heating costs.
Because they use a small heating element, desiccant dehumidifiers do consume more Electricity than their rotary counterparts, making them slightly more expensive per hour to run (The average running cost of a Desiccant Dehumidifier in the UK is around 4p per hour). However since they return heat to the room, raising the room temperature and so reducing the energy input required from other forms of heating, those running costs are mostly recouped and shouldn’t be a cause for concern.
The other advantage of desiccant dehumidifiers, is that they are quiet running and so ideal for a bedroom or other living area, as they produce no more noise than a small desk fan, compared to a rotary type which can be very noisy in operation.
When comparing running costs, also note that many modern dehumidifiers now have a ‘humidistat’ control. This works much like a thermostat on a conventional heater, and senses the humidity level in the room, and so switches on the dehumidifier on only when its required, saving additional energy.
My own experience with a desiccant dehumidifier are that they will initially run at full power for between several hours and a full day and remove around 5 litres of water whilst the humidity level is initially reduced down to the level selected on the ‘humidistat’, after which the dehumidifier will only operate when the humidity levels increase above the comfort level selected on the control panel. I set my dehumidifier to keep the room at no higher than 50% rh and although my dehumidifier was left on for 24 hours a day, after the initial running period to reach the desired 50%, it was only actually physically running for around 2 hours, making it very cheap to run.
I have tried several desiccant dehumidifiers on the market, and the two which I highly recommend personally, and of which I found to be the most effective at not only removing moisture but also heating the room are the Ecoair DD122FW Dehumidifier and the one which I am currently using, the Meaco DD8L Junior