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We had a humidity issue in our rental flat last winter - every morning all the windows were wet, and we had mold in the corners and behind the couch. (Despite venting 3+ times a day for 10+ minutes - which was really uncomfortable because of the cold.) The apartment has 55m2, is floor-heated, family consists of 2 adults and a toddler. We had to hang our clothes inside to dry, because outside they only would get damp. The humidity sensor I installed showed up to 80%RH, with 10+ minutes of venting I could barely get it under 60%RH.

This winter we'll try to remove all the houseplants from the flat and buy a tumble dryer for the clothes. Questions are:

  1. what kind of tumble dryer do we need?

    Vented dryers are not an option (unless it stands outside in the cold) because the apartment is not ours and I'm not allowed to make modifications for the vent. So I guess I'm left with condensation dryers and heat pump dryers. Efficiency is less of an issue, but I'd like to avoid damaging the clothes. Also don't know what kind of air circulation they need - if I have to vent the whole apartment to keep them working, then they are a no-go. Can any of them be installed in a bathroom with no direct ventillation (no windows, only some kind of an inefficient active ventillation)? Can the condensation dryer get hot enough to injur a toddler?

  2. will it reduce the humidity at all?

    I'm not sure how humid the exhaust air will be. I guess it should contain less water, than if we dry the clothes in the living room. But not sure if it will work at all, if the living-room humidity is constantly (hopefully) between 60-70%RH.

isherwood
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G. B.
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    Go with a dehumidifer (one with a compressor not the fake ones) as one answer says. Leaving the dehumidifier overnight in a room with drying clothes will dry them till morning. It consumes roughly 1kwh/night. More efficient than a tumble dryer. – Beni Bogosel Oct 17 '23 at 14:21
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    Sounds like you mainly have a ventilation and insulation issue. Too little throughput of air and too much throughput of temperature causes a lot of issues in combination. – Stian Oct 17 '23 at 15:58
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    Would putting a vented drier next to a window and running the vent hose out of it be a possibility? To minimize heat loss while doing so you'd want to have a blocking panel of plywood or equivalent covering the remainder of the window opening. – Dan Is Fiddling By Firelight Oct 17 '23 at 19:24
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    Not the question asked, but you might consider centrifuging your clothes before hanging them if an unvented dryer does not work out. In a lot of asian countries where dryers are rare people use centrifuges before hanging their clothes. They spin significantly faster than the spin cycle on a washer and get clothes significantly dryer than a spin cycle does. – Chuu Oct 18 '23 at 17:25
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    @Chuu in an old-fashioned UK laudromat the attendant required you to centrifuge your clothes before putting them in the dryer. You would receive quite a tongue lashing if you disobeyed this rule. – D Duck Oct 18 '23 at 17:59
  • That sort of centrifuge is better known in the UK as a spin dryer. They're good, better than the spin in a washing machine, but not much better when compared to modern washing machines in which 2000rpm+ is common. I touch on that in my answer, and FreeMan expands on the idea in a comment (@chuu) – Chris H Oct 18 '23 at 19:45

2 Answers2

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A more compact alternative worth a mention is a dehumidifer. I dry my washing indoors in UK winters, without a tumble drier. For efficient drying, shutting the damp washing and dehumidifer in a room works well; at other times, allowing air to flow between rooms drops the humidity in all of them.

Unlike a tumble drier it will also deal with cooking or shower steam if you don't have a good extractor fan.

Another space-saving option I should mention for completeness, though I haven't used one myself, is a washer/drier in place of your washing machine. They're probably better for occasional drying rather than being your main method.

Whatever you use, you can help the process along by making sure your washing is spun as hard as the care instructions and your washing machine allow. Really wet things that can't be spun benefit from a couple of hours to start with outside unless it's raining or freezing.

Chris H
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    This is by far the best way to go. One or more dehumidifiers will control your humidity better than anything in winter and will speed up your indoor clothes drying time without a big investment in a condensing dryer. – MTA Oct 16 '23 at 16:51
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    A second run through the spin cycle will help with the drying, too. – FreeMan Oct 16 '23 at 17:23
  • I wasn't impressed with the condenser drier I had, but we're probably talking about a 15-year-old design. It out a lot of heat and some humidity into the room. – Chris H Oct 16 '23 at 17:52
  • Humidity is Relative. It works where winter means +/- 4C. It is a poor solution where winter means -15C. – DelphicOracle Oct 16 '23 at 17:59
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    @DelphicOracle are you referring to my minor tip about starting really wet stuff outside (when I said "unless...freezing")? Because clearly everything else would be used indoors, at room temperature. – Chris H Oct 16 '23 at 18:38
  • If you don't mind the clothes becoming frozen stiff, drying outside in freezing weather actually does get things drier (never left them long enough to get all the way dry, but it made a significant difference in how much more drying they needed, in a place where winter means -20°F sometimes.) Sublimation happens. – Ecnerwal Oct 16 '23 at 19:24
  • @Ecnerwal I've never had it cold enough for long enough, but I have left things out over an unexpectedly cold night then had to get them dry. Condensation onto the frozen things didn't help that process. – Chris H Oct 16 '23 at 19:28
  • This. I've owned an electric tumble dryer for 40 years, and for the last 20 its sat in the garage holding up a toolbox and hiding christmas presents. A closed-off room with a dehumidifier running inside works wonders - I use one to keep an ensuite/shower room dry and sort my wet riding clothes for the next day. – Criggie Oct 17 '23 at 00:07
  • Washer/dryers IME are neither good washers nor good dryers. – Jack Aidley Oct 17 '23 at 08:08
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    @JackAidley The one or two I've used for washing have done that OK. My drying use case would be to occasionally dry a few things in a hurry, so one might be useful (I might think about it when my washing machine breaks beyond repair). For the OP they're probably less suitable, but in a small apartment the calculation can be different, and I've known people who wouldn't be without. I really do mention them more for completeness though – Chris H Oct 17 '23 at 08:29
  • In freezing weather the air - indoor and outdoor becomes very dry as the moisture is frozen out. The indoor air is dry as the minimal humidity in the outdoor air is reduced further as it is heated and thus can support more moisture. – D Duck Oct 18 '23 at 18:01
  • @DDuck but a modern home doesn't draw in much outside air, so the humidity goes up from many sources indoors. And don't forget that winter doesn't always mean freezing everywhere. It can mean wet weather with high (outdoor) RH but still quite cold. Pulling in lots of damp 5°C air, for example, won't drop the humidity of a 20°C home very much before the indoor temperature gets unpleasantly low – Chris H Oct 18 '23 at 19:42
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Heat Pump or Condensing Dryers will not add meaningful moisture to your apartment.

Both Heat Pump and Condensing Dryers are closed loop systems, recirculating air inside the unit. Both use a refrigerating system to create the cold surfaces for condensing.

  • Condensing Dryers use a heating element to increase the temperature inside the drum to release moisture to the air. The moist air is passed through a condenser which turns the water vapor into droplets that are either collected in a pan or drained.
  • Heat Pump Dryers use the ambient air temperature as the heat source. It collects the heat from the room to create the heat source to dry the clothes. It removes the moisture in the same way as the condensing dryer.

Heat Pump Dryers take a little longer to dry clothes because they do not add extra heat to the drying process. They will be cheaper to run because they do not use resistance heaters.

Both will do the job.

If you use the machine's pan and forget to drain it, you will be adding moisture to your apartment.

I used a Heat Pump Dryer on a recent trip and found the dry times acceptable. Your experience may vary.

FreeMan
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DelphicOracle
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  • The collection pans are normally all but sealed, so won't add meaningful amounts of water to the air, but it's as well to empty them after each load anyway – Chris H Oct 16 '23 at 16:38
  • Note that a Heat Pump drier will extract heat from the house that will need to be made up for by the home heating system. The Condensing Dryer won't tax the home HVAC system, but will still uses energy to create heat. – FreeMan Oct 16 '23 at 17:25
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    @FreeMan the heat, along with that from the pump itself, will end up back in the house, at the latest when you take clothes out. They don't (in the general case or to be suitable here) vent warm air outside. Any water going down the drain will only take a little heat, as it has to be condensed on a cold surface, and if collected in a tank, even that heat escapes into the room. – Chris H Oct 16 '23 at 17:55
  • @ChrisH: If a machine removes 1kg of water from some clothes, and the water is never drained, it will either go back into the air or stay inside the machine forever, and I doubt machines have an infinite capacity to hold water. – supercat Oct 17 '23 at 16:07
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    @supercat obviously you have to empty a tank, or the machine will switch itself off (there's a sensor). Typically they need emptying every 1-2 loads. If you empty the tank immediately, the water might be a little warm; if you do it before the next load, it will be room temperature. Or connect it to a drain, if the machine has that option, then the water will drain away slightly warm – Chris H Oct 17 '23 at 18:59
  • @ChrisH: It sounded as though you were responding to the "If you use it and forget to drain it, it will add moisture to the apartment", and your comment made it sound as though forgetting to drain them would neither add moisture to the apartment or have other consequence. – supercat Oct 17 '23 at 19:05
  • @supercat, OK, my first comment, not the more significant one. It's preferable not to let the tank fill up part way through a load, because the hot damp clothes will sit in a heap in the machine. Some tanks get a bit awkward when full as well. – Chris H Oct 17 '23 at 19:10
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    @FreeMan and DelphicOracle seem to have no idea how heat pump dryers work. A heat pump drier doesn't "take" any heat from ambient. Both a heat pump and condenser dryer work by an internal cycle of heating air, passing it through the clothes, and condensing it in a cooled condenser. The condenser drier uses a resistive heater and cools against ambient air. The heat pump drier uses a heat pump to both heat the air and cool the condenser, increasing efficiency. In either case, all the power put into the system will end up as heat in your room. (1/2) – Sanchises Oct 18 '23 at 09:25
  • Only a vented dryer will tax your HVAC in winter because it draws in ambient air and expels it out the vent, which will need to be replaced with cold outside air. All dryers will release some moist air into the room because they need to vent some air from the condenser and replace it with ambient air, or the temperature inside the dryer would keep increasing indefinitely. The condensation efficiency is posted on the label (at least in the EU) (2/2) – Sanchises Oct 18 '23 at 09:31
  • @Sanchises Some heat pump dryers, I believe, don't vent any moist air at all. Instead, they can use ambient air to cool the hot air inside. (FWIW, I have such a dryer. It has no vent, but does have an intake at the front (and presumably an exhaust somewhere else), with a fan, to suck in ambient air for cooling purposes.) Also, I presume that if there's any danger of overheating, the dryer can turn off the heat pump for a bit. – Steve Melnikoff Oct 18 '23 at 11:27
  • @SteveMelnikoff I just meant that if your heat pump uses 1000W, then this heat needs to go _somewhere_. Although to be honest I'm not entirely sure in which part of the thermodynamic cycle this heat is rejected from the system. I would guess it's air that's been run past the condenser (so fairly dry but not exactly bone dry), which has the added advantage of introducing some fresh air into the laundry to eliminate odours. – Sanchises Oct 18 '23 at 12:03
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    Aren't _heat pump_ or _condensing dryers_ essential just a _dehumidifier_ in a box with a revolving drum. Where your clothes are - in the room or in a box - is really the only difference. The heat pump & condensing types win because they force warm air thru your clothes to improve the moisture transfer. – D Duck Oct 18 '23 at 18:06
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    @d-duck And the clothes that come out are not as stiff as cardboard. – DelphicOracle Oct 20 '23 at 12:45