Dehumidifiers & laundry... how to cut both drying times AND costs
Dehumidifiers can be a cost-effective way to dry laundry indoors, but only if used in the right way.
They are expensive to run, if not used in the right way.
Costs, and especially drying times, can be reduced SIGNIFICANTLY by following the tips in this article.
The tips here are based on research and geeky tests I have recently carried out using a compressor type dehumidifier (the most common type).
I reduced the drying time from 7 hours to 4 1/2 for a medium-sized mixed load (including some towels). At the same time the energy costs reduced from 68p to 44p.
The tips here are all aimed at helping the dehumidifier do its job more quickly, so that it can be turned off sooner.
A wash load can hold anywhere from 0.7 litres to 3 litres of water (I've actually measured this), so having the right-sized dehumidifier is important. If it's too small, it won't do very much at all, except cost you money, and not deal with damp properly.
If you are thinking of getting a dehumidifier, the section further down has some buying tips.
The testing I did was with a 360-Watt dehumidifier that costs around 10p an hour to run and officially extract 11 litres of water a day. It was a little oversized for the job and from research I think a dehumidifier of even half that power would actually do the same job for a lower cost.
Conclusions and tips
Tips that have the most effect
Use a dehumidifier in the smallest room you can. I found drying laundry in a 6' x 8' room was much cheaper and quicker than in a 10' x 12' room. The smaller room concentrates the warm, dry air around the laundry and the room gets a LOT warmer. Some dehumidifiers to state they shouldn't be used in a room smaller than 4 square metres so do check the owners manual for your machine.
When doing laundry in a room with a dehumidifier, it is essential to keep the door and windows shut, to concentrate the dry air. The above tests were ALL in a room with the door and window shut. Drying times and costs would have been much poorer than the figures above if I'd left the door or window open.
A draughty room will make it much harder for the dehumidifier to do its job so even close the window trickle vents if they have them.
Sidenote: If you use a dehumidifier to deal with general damp and condensation issues, windows and trickle vents should be shut in the areas where you use it.
Room temperature is very important for a compressor dehumidifier to operate efficiently - ideally, 20C or above. Warming a room up specially to dry your laundry, though, isn't sensible. If the room isn't quite warm enough, don't worry: the dehumidifier will warm it up a little once it gets going.
Avoid using smaller (10-12 litres per day) compressor type dehumidifier in a room that is under 15C because it simply won't be efficient: drying time will be slow and the energy costs much higher. A cold conservatory is definitely the WRONG place to use it.
Much larger (20-25 litres per day) dehumidifiers will work reasonably well down to 10C but these are probably much bigger than is needed for helping with laundry.
Rarer desiccant type dehumidifiers work fairly efficiently at normal room temperatures but are generally better than compressor types in really cold conditions (down to 5C). They are better suited for helping with general damp issues in a home rather but are also good at laundry, and users like the fact that they do blow warmer air than compressor types.
Using a dehumidifier to help dry laundry in a room with open stairs will not work well. The warm dry air created by the dehumidifier will rise and vamoose upstairs away from your laundry.
Similarly using a dehumidifier in a room with high ceilings will not work well at all.
Here are a few suggestions for ways of speeding the drying process further.
Pointing a desk fan at the laundry improves drying time significantly. Although the fan uses energy, it is quite a small amount, compared to the dehumidifier, and because the laundry dries faster, you can turn the dehumidifier off sooner. Since originally posting this I have seen many comments that agree that this makes a very useful difference to drying times and overall costs.
Other tips that will also help
Read your dehumidifier instruction manual (although some are awful..)! If it has any smart features to help minimise energy use, try to get to know them. Contact the manufacturer with any questions if the manual isn't clear. It is also important to read the manual to understand what safety precautions you need to take when using one as these might vary from one manufacturer to another. Meaco for example state in their owners manual that their products should not be used in a room less than 4 square metres. This will be a requirement for any dehumidifier using R290 refrigerant, which affects most dehumidifiers sold from Jan 1st 2020. Others may have other specific requirements that need to be observed.
Some dehumidifiers have a 'laundry' mode. This uses very little more energy than the auto mode. I found it DEFINITELY dries the clothes faster overall in this mode. I got my quickest results by far using this mode, but again you need to keep the door and windows shut.
Stand the dehumidifier as near to the laundry as you can (though check what the manual for your specific machine says on this). If it has a fan blowing warm air, point it at the laundry, if you can. If it blows air out the top, see whether you can hang the washing on a rail or ceiling rack above it, though don't ever hang dripping washing over a dehumidifier as this would be a safety risk.
Don't be alarmed if the dehumidifier doesn't actually blow warm air all the time. It is designed to dry the air rather than warm the room so just let it do its job. Most compressor type dehumidifiers will only warm the air passing through them up by 1 or 2C above the room temperature. (Desiccant dehumidifiers are different - they do blow out much warmer air).
A dehumidifier will find it harder to do its job in a poorly insulated room.
If you have curtains draw them. If the radiator is on, tuck them behind to help the heat from the radiator help the heat from the radiator flow into the room and help the dehumidifier.
If you have full length curtains like those in the photo below. If the heating is ON leave the curtains OPEN to keep the heat from the radiator in the room and help the laundry. If the heating is OFF, then draw the curtains to reduce heat loss from the room which will help the dehumidifier a little.
Stand the laundry in the sunshine, if you can.
If you can feel a draught under the door, put a sausage dog (or even something as simple as a rolled-up jumper) at the bottom of the door. This will help the dehumidifier do its job.
If an item of laundry feels heavy when it comes out of the washing machine, it is because it is holding lots of water, which means it will take longer to dry. If you can dry heavy items outside, or in other ways (e.g. simply air drying in a room with a window open for ventilation), you will save money.
Doing an extra spin cycle doesn't actually remove much extra water. I have a 1400 spin speed machine and have done several tests weighing the laundry dry, then at the end of the wash, and then again after a second spin cycle. The amount of water a second spin removes is small. The best result was with fluffy cotton dressing gowns. Our adult gowns each held around 700ml of water after a wash, and re-spinning removed only another 50ml which is around 3 tablespoons of water. So, given that a spin cycle is the harshest thing a washing machine does to itself personally I really wouldn't bother - it's just not worth shortening the life of the machine. A machine that can spin at 1600 might get more out but I doubt it would be much. For info, if you DO want to do a second spin, the energy cost is under 2p.
Put heavier, wetter items at the top and on the outsides of the drying rack, especially if it helps them get better air flow from the dehumidifier. Rotate items around part way through or rotate the whole rack round if some areas are drying quicker than others. Turning harder to dry items inside out will help too.
From the experiments I've done, I don't think it makes sense to run the dehumidifier until the laundry is bone-dry. In a small, closed room the air gets really warm and dry, so switch off the dehumidifier a little before the end, keep the door shut and let the laundry finish air drying for an hour or two.
If you use a heated airer at the same time as a dehumidifier this will speed up drying further, but the costs per hour will be higher so keeping an eye on the laundry is really important to avoid unnecessary costs. In this situation it is REALLY important to have a dehumidifier that is powerful enough for this job. If you use what are described as "low power/eco" dehumidifiers (often around 40 Watts, using a technology called "Peltier") you will find the dehumidifier simply won't cope and you will find you have to open a window to get rid of the moist air. If you have to do that then you might as well unplug your dehumidifier and just use the heated airer, as dehumidifiers only work efficiently when you can keep the window shut.
If you have had a dehumidifier for a while, check that the inlet filter doesn't contain any fluff. It is usually easy to get to, behind a plastic grill.
If a dehumidifier doesn't have smart shut-off features or timers. Do NOT use plugin timers with compressor dehumidifiers as turning them on and off remotely does actual affect their long term reliability.
Dehumidifiers can be quite energy-hungry, so to keep track of costs, why not use an energy-monitoring smart plug like these? They are incredibly easy to set up and use. If you have a smartphone, you can monitor your use and even control your dehumidifier remotely.
My tests were with a 360W dehumidifier, but all the tips above should work with any model. See the buying tips section below for my views of dehumidifier sizes.
What I have written won't cover everything. Please get in touch with your ideas about what does and doesn't work, so that I can update this article.
Towels in particular are very slow to dry, so why not consider using smaller towels as this also reduces the amount of moisture in the air when drying and the chances of damp issues. Also question whether you are washing towels too often? I know someone who washes towels after just one use. The laundry industry recommends every 3-4 uses (though in our house we probably use towels 7-8 days before washing).
Dehumidifier buying tips
A wet laundry load can hold anywhere from 0.7 litres of water to 3 litres, but typically between 1 and 2 litres. Get a dehumidifier with a collection tank of 2 litres or more.
Different makes of dehumidifiers have their outlet air vents in different positions. Ideally, you want the vent to point AT your laundry, so choose one that suits the position of your drying rack, or where you hang clothes.
A dehumidifier that switches off after as set number of hours is a really good way to keep control of costs.
As mentioned above there are small 'low energy' dehumidifiers on the market that use as little as 40 Watts. I've not tested one but I have done enough research to know they simply will cope with the amount of water evaporating from laundry and just are not worth using to help with laundry. Using one of these would mean you'd still have condensation and damp issues, or you would find that you would need to open a window to help it do its job. They have very small collection tanks on them, which is also a sign that they are unable to remove much water.
If you are thinking of buying a dehumidifier, it is important to know that there are two main technology types. It will always be clear in marketing literature and in instruction manuals which type they are:
Compressor dehumidifiers - these are the most common. They are not so efficient at cooler room temperatures. The ideal is above 20C. They start to become pretty costly and slow to do their job below 15C, and will be virtually useless when it is 5C or colder. They are REALLY efficient the warmer the room above 20C, (much more efficient than desiccant dehumidifiers).
Desiccant dehumidifiers - these are rarer. Although these work better at much cooler temperatures (below 10C) than compressor types, the opposite is also true: compressor ones are more efficient over 20C. If you prefer a cooler temperature in your home or want to use a dehumidifier in a cold area with damp issues you are trying to deal with, then this type are probably best for you. I have not tested this type and cannot comment on how much energy they use.
I normally avoid making specific product recommendations, but I'll make an exception in this case. There is a Meaco compressor dehumidifiers do look very impressive on paper. I have seen detailed technical information on Meaco products and have to say I am very impressed and they certainly look as though they should be even cheaper to run than the dehumidifier I tested.
The geek zone: information about my experiments
The dehumidifier was a 360-Watt Silverline compressor type model (no longer in production), with a stated performance of 11 litres/day dehumidification capacity at 27C 60% RH). It uses the established and common R134a refrigerant. For info, the Meaco unit mentioned above uses R290 refrigerant.
Over ten days I carried out experiments in two rooms: one was an average-sized bedroom, the other a small utility room, in a 1950s fairly well-insulated house with good double glazing and 8-feet-high ceilings.
For each test I used an identical 3kg mixed wash load of cotton towels, cotton shirts and clothes made of man-made fibres. Each wash load held around 1.7 litres of water.
Before and after each test, I recorded the energy used by the dehumidifier, humidity (RH), and temperature in the room. I also recorded the weight of laundry, before and after, to work out how much water was in it, and weighed the water collected in the dehumidifier tank. Based on the weight of water in the collection tank in each test, the water capture rate was between 200 and 230 ml per hour.
The weather and room conditions were very similar each day. There was no heating on, and there was a stable background temperature of around 20C in the room over the 10-day period.
Where appropriate, the same physical layout of laundry items on the drying rack was used.
When I considered the clothes were 'dry enough', I stopped the dehumidifier and weighed them. To my surprise, I found that this subjective judgement was remarkably consistent: the washing was always around 92%-93% dried (i.e. holding just 7-8% of the original water content).
One key thing I learnt: the dehumidifier I used consistently cost 10p an hour to run, regardless of how dry the laundry actually was. So, the key to reducing costs is to help it do its job more quickly and reduce its running time. I wasn't able to try all the tips above in one experiment, but believe drying time could be brought down to 4 hours if they were all combined.
The unit I used may have been a little oversized for what I was doing. A lower power unit (say in the 200-250W range) might give a similar performance while using less power. This is just a hunch and I have no way of proving this without testing one.
Using a dehumidifier does warm the room up (sometimes by several degrees). If the central heating is on, then this will mean the heating won't need to work as hard, which will save on heating costs a little, partially offsetting the energy costs for the dehumidifier itself. For the sake of simplicity in the information above, I have left this saving out of the maths.
All costs assume an energy cost of 27p/kWh (the standard rate tariff from Oct 2023)
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