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I know there are a few questions which are similar to this, but I'm asking for facts, about which is definitely better.

We have only one clothes rack but we have a lot of laundry to get through.

Each load needs washing and drying separately because only load fits on the rack (obviously heavy duty items go straight on the radiator).

My question is this: When the weather is cold which is better, putting the clothes rack out on the balcony or in the front room?

Some assumptions:

  • It's around 13 degrees Celsius outside
  • It's around 19/20 degrees Celsius inside
  • There is a light breeze outside, but it's not sunny
  • I don't have a dehumidifier
  • By "better" I mean quicker

There is a partial answer on this question: How can I get damp clothes to hang-dry faster in the home? but I am looking for hard facts.

  • Hi Bee, Welcome to Lifehacks. – Stan Nov 1 at 14:07
  • My only suggestion is what I ended up using. A mini washer/spin dryer that runs on AC power that I can convert to solar for use off-grid. Works great. Small loads but whatever I spin comes out nearly dry and takes about an hour to dry completely inside, on a drying rack in 68 F small cottage. – M.Mat Nov 3 at 9:57
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    @Michael the OP is in the UK where wet central heating is commonplace - radiators are full of water at about 60°C, and unless the coating is chipped corrosion shouldn't be an issue – Chris H Nov 4 at 9:37
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    More of a comment than a hard fact, but you really want a dehumidifier. I've got two small ones which are about the size of 3 shoe-boxes stacked on top of each other, and they are more than adequate for a 3-bedroom bungalow. And dehumidifiers plural are generally better - you can remove damp from the house more effectively with smaller ones in high-humidity areas than one big one somewhere central. Don't buy one which has a wall-wart power supply though, because they won't do anything. You want a proper mains-powered one with a proper compressor. Mine were £70 each, so not too pricey. – Graham Nov 4 at 10:37
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    Are you sure you want only the quickest way, not minding e.g. mold developing into your house because of the moisture? I always hang laundry outside because of that (not that it's the only source of moisture that can cause damage of course). – FunnyJava Nov 4 at 12:26
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The best hard facts are the ones you establish for yourself under your specific conditions.

One experiment is worth a thousand good opinions. — Bill Nye, the science guy.

Determine which location will be more efficient (easier, better, faster, etc.) by taking two identical cake pans filled with the same amount of water and placing each in the locations you want to compare.

After you wait a bit, compare the two water levels by weight or by refilling to a known level (volume).

You will now have the hard facts you need regarding which location will serve your purposes "better."

Have fun. Good luck.

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    @Bee Note: experimenting with two identical pieces of cloth (e.g. two identical towels; two undershirts; etc) which have been wetted with identical amounts of water is probably a better experiment than a couple of cake pans. Using cloth will allow you to place them in nearly the same location (including height) as tehy will be in on your drying rack. Given that one is outside in the wind, the effect of the wind will probably be quite significant, but it will vary significantly based on the positioning of the items, which really can't be duplicated by a bowl or cake pan of water. – Makyen Nov 1 at 21:19
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    @Makyen, You seem to have missed the detail that the OP has only one clothes rack for the experiment which must be either inside or outside. This makes "identical" difficult to reproduce in your "improved" experiment. – Stan Nov 2 at 4:22
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    @Makyen and Stan: the OP only has one full rack, but I'd suggest rigging up a make-shift equivalent to hang one shirt inside for one or a couple experiments. It's more effort than you'd want to do regularly for your full laundry, especially for multiple items, but one coathanger on a string indoors as a comparison for the rack outside should give you good data and isn't a lot of effort for one shift for a few experiments. I'd suggest doing the make-shift rigging inside because without wind it's probably less sensitive to the fine details of the rack. – Peter Cordes Nov 2 at 7:29
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    I don't thing this experiment will tell you anything about drying cloth, because cake pans are very different from clothes – njzk2 Nov 3 at 0:07
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    @Stan the similarities between the physics of an evaporation pan and a section of arable land aren't perfect, but they're a whole lot better than the similarities with drying clothes. At least arable land still has a single sky-facing evaporation interface on one side of a comparatively deep source of moisture, and farmers are probably mainly interested in a finite percentage of that moisture evaporating away. Your clothes have an evaporation interface either side of a comparatively tiny "depth" of water and you are interested in that water's evaporation as its mass approaches zero. – Will Nov 4 at 12:39
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Assuming that it’s dry outside, windy and cool is always better than stagnant air.

The rate of evaporation depends on two factors:

  1. The absolute amount of water the air can hold and
  2. The difference in humidity between the laundry and the air around it.

While cooler air can hold less water than warmer, the relative humidity inside is very often way higher than outside, typically because we humans produce moisture in our daily activities, from simple exhalation to cooking and bathing. And hanging laundry will add more water, which can bring the air to quite high levels quickly.

Outside, the absolute amount of air is so much, that combined with the movement due to the wind, the laundry will dry quicker - if drying indoors, you’ll find yourself opening the windows regularly, to bring the humidity down again, so you can as well put the rack outside.

  • One caveat is that if the temperature is low enough to freeze the water then evaporation basically stops. – barbecue Nov 2 at 16:18
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    @GoodbyeMsChipps that’s actually wrong - frosty winter air is very dry and laundry dries exceptionally well. Yes, it freezes, but it dries. The underlying principle is called sublimation. – Stephie Nov 2 at 16:21
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    Sublimation is much slower than evaporation. – barbecue Nov 2 at 16:29
  • "[T]he relative humidity inside is very often way higher than outside." Citation needed. Not true where I live, and if to be believed, several (1,2) sources show more than half the United States having higher than typical RH maintenance level by HVAC (40-50%). – bishop Nov 4 at 7:41
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    @bishop Yeah, that part of the answer is very location-dependent. In Arizona, it will almost always be true. In South/Central Florida, it will almost always be false. Definitely false during most of the year where I live in TN. The HVAC systems condense the extra water and dump it outside in order to keep the indoor RH at a much more pleasant level than the 80-90% that can often be found outdoors in the spring and summer. – reirab Nov 4 at 17:15
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The criterion I would use is the outside relative humidity. If it's very humid, then clothes will probably dry just as well indoors, and there may even be a risk of rain. If the humidity is below about 75%, outside drying is probably more effective even if it's somewhat cooler.

The exception I would make to this is if the outside temperature is near or below freezing. The maximum density of fresh water is near 4°C, which I think is a reasonable cutoff point. Frozen moisture is much harder to get out of clothes than when it's liquid, so in this case it's always better to keep them indoors. (Sublimation, mentioned in another answer, only occurs at useful rates at pressures far below normal atmospheric.)

  • Hi Chromafix, Welcome to Lifehacks. – Stan Nov 2 at 22:58
  • Erm... “no” to the sublimation being not useful statement. Generations of housewives can attest to the fact that sublimation works perfectly fine for laundry at frost and unfortunately also for frozen food, aka freezer burn (or at least as one contributing factor). – Stephie Nov 3 at 21:12
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    @Stephie Still not useful over the timescale the OP wants though. They probably wouldn't find it acceptable that their clothes take weeks to dry. – Graham Nov 4 at 7:53
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    @Graham erm, from my own experience: bedsheets at -10C: two to three hours on a windy day with intermittent sun and clouds, jeans perhaps four to five hours? I feel that’s a reasonable drying time. – Stephie Nov 4 at 7:56
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    @Stephie Interesting. In England it certainly doesn't work that way on a cold day, but we're not so often sub-zero during the day unless you go somewhere higher-altitude. There can be ice or snow on the ground, but the air temperature is generally above zero and correspondingly damp. With your experience, Chromatix's answer would probably be more accurate then to say that the daytime outside temperature temperature needs to be below freezing, because temperature and humidity are closely linked that way. – Graham Nov 4 at 10:32
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Simple solution: compare the relative humidity

The relative humidity is the major determining factor here! To be more precise, the lower the RH, the more quickly water will evaporate into the air, so you want the environment with the lower RH (as a percentage).

Complicating factors

There are several factors that can affect your decision, however:

Interestingly, RH is temperature dependent-- hence the term relative humidity. RH is a measurement of how much moisture is in the air vs. how much it could have. The warmer it is, the greater the absolute moisture content can be in the air. Therefore, if you start off with a house where the temperature and humidity are the same throughout, you could reduce the RH in one room by raising the temperature with a space heater, stove, or fire. Outdoors, barring weather fronts, you are more likely to encounter changes in temperature and RH that follow the time of day. (Make sure you don't leave clothes out overnight or water can condense back on them if it gets colder than the dewpoint, which is when the RH hits 100%.)

Air movement also makes a big difference. If there is no air current the air containing the water vapor will remain close to its source, with the result that the wet clothes will be surrounded by a zone of high RH and therefore cannot continue to dry at the same rate. Usually there is much more air movement and therefore air exchange outdoors.

Air conditioners prevent spikes in RH inside your house by collecting condensed water from the air as it is cooled down, which means that it is constantly drying out the air in your house-- but it usually just keeps the RH constant because the temperature is dropping.

Clothes spread out for maximum surface area and air flow should dry eventually in either environment, but not so well, e.g., in an indoor swimming area or locker room with tons of showers in constant use-- the evaporation of those water sources will keep the RH elevated. A minor consideration: mold growth happens at high RH, but things need to be constantly damp for about 48 hours before it becomes a problem. If it's really humid indoors and out, consider setting up a heat source to dry out (lower the RH of) the air.

If you want to dry your clothes inside, you'll have the most success if you hang clothes in bigger, warmer rooms, leave doors open between rooms, and set up fans (or dehumidifiers, if you want to invest).

Experiment: which is best for your situation?

This changes with the weather, so you'll have to make a new assessment each time.

If you want to figure out precisely which is better for you via quantitative experiment, you can buy a cheap thermohygrometer to measure the RH in your house. (Here's one for $5 on Amazon, though I encourage shopping locally if you can!)

You can place it in the space where you would dry your clothes and compare that reading to the published weather stats for the general outdoor RH that day and time-- or you can take your handy new hygrometer outside and get a new reading for comparison (give it a minute to adjust). If they're not wildly different, you'll probably get faster drying (not to mention a little bit of natural fabric softening) where there is more of a breeze.

You can also try a practical experiment of drying clothes inside and checking the RH next to them as they start to dry-- the space they are in will probably increase in RH a bit unless you have good air movement; if your indoor drying space gets much too humid you might set up fans for circulation, or just plan to dry clothes outdoors.

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    Hi wordsworth, Welcome to Lifehacks. – Stan Nov 3 at 4:27
  • I didn't realise they were that cheap. Big fan of experiments might have to try it out! – Bee Nov 4 at 12:36
  • @Bee, they're great if you need a ballpark figure! There are much better ones available for both precision and accuracy, but that's not necessary for this project. – wordsworth Nov 5 at 4:01
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A technique used in some parts of Europe to prevent wintertime development of indoor mould is to ventilate the dwelling once or twice daily and to keep all windows and doors closed at other times. For example, Germans call this Stoßlüften or "shock-ventilation". This also replenishes the home with oxygenated air owing to the windows normally being closed in winter.

The process relies on periodically displacing as much as possible of the interior air -- which is comparatively warm and moisture-bearing -- with fresh air from outside. The new air is allowed to then warm up and absorb water vapour from indoor activities like cooking and laundry. And warm air can hold more moisture, and thus appears drier to clothing, than the same air when cold.

Recommendations are to open all windows and doors on opposite sides of the dwelling for 5 minutes or more so as to cause a draught that carries the interior air away, but windy conditions could reduce this time. It won't work well in misty conditions.

I have used this technique to dry laundry, however, if the temperature and RH differences between inside and outdoors are not significant then the effort can be in vain, and outdoor drying might be more effective. Your local conditions could be borderline. To reduce the burden, perhaps place the laundry in a room with a radiator and shut all doors and windows to the room, then experiment with briefly ventilating the room every 2 hours.

If the technique works for one rack of clothes then it will scale to multiple racks.

Advice from a German government department about ventilation (in German):

Shock-ventilation

Translations of the text:

Proper ventilation - like so:

  • Shock-ventilation several times a day with windows wide open.
  • Best by opening opposite windows ("draught").
  • Ventilate with the radiator turned off. (I ignore this step for brief occurrences.)

Source: https://www.bmu.de/themen/gesundheit-chemikalien/gesundheit-und-umwelt/innenraumluft/richtiges-lueften-und-heizen/

  • Hi crw, Welcome to Lifehacks. – Stan Nov 4 at 23:07

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