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During the winter, I often get high humidity in the home. Especially with multiple people living here, and cooking, or having showers etc.

This leads to condensation on the windows, and moisture on other surfaces, and maybe mould growing.

So how to decrease the humidity? Obvious answer is a dehumidifier, but how much electricity would that use? Or open the windows, but that lets cold air in, and often the outside humidity is nearly as high anyway. Any other options?

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    In the winter, I wouldn't discount using a dehumidifier - the by-products are water (which you can use for flushing toilets and/or watering plants) and heat (which will off-set need to use other heating sources). – LShaver Nov 14 '16 at 16:53
  • Weigh the costs of a humidifier vs property damage. An extra hundred bucks for electricity a year will be far more affordable than a thousand dollar renovation to get rid of molding drywall and water damage. – pheidlauf Nov 15 '16 at 18:00
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The outside relative humidity may be almost as high but the absolute amount of water held in the air is lower. So removing the most humid air is effective. That's the principle behind shower extractor fans and cooker hoods. Replacing a lot of lower humidity air with outside air lets a lot of heat out.

A dehumidifier uses a couple of hundred Watts when it's actually doing something (i.e. when it's making a noise), but this all contributes to heating the house, as does the latent heat recovered from the condensed water. This is a small domestic model that can remove a few litres a day; bigger ones are of course available but they're noisy.

So we use a dehumidifier for slightly more of the year than the heating is on; in summer opening the windows in preferable. In winter ours doesn't run flat out (almost all have humidistats) unless we've got washing drying. Cooking steam and shower steam are at least partly removed by fans as well.

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    That last thing (*removing cooking steam and shower steam with a fan) is what I would try first: you remove the moisture peak at the same time you generate heat - the period is limited - your (noticeable) heat loss is lowest. And a fan uses little power. – Jan Doggen Nov 14 '16 at 14:08
  • @JanDoggen IME that works well if adding/fixing an extractor fan is an option. I didn't want to assume that the OP could change the framework of the building (the houses I've come across with the worst humidity problems have all been rented). Opening windows seems less effective than a fan, but my main reason for not suggesting that is that if you open the window when you leave the shower, you tend to forget to shut it again, thus letting all the heat out and freezing the next person to use it. – Chris H Nov 14 '16 at 14:11
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I agree that at least a couple extractor fans or vents are a good idea, in both the kitchen and bathroom. (And does the clothes dryer vent outside?) Look into Heat Recovery Ventilators (HRV) and Energy Recovery Ventilators (ERV) if you're worried about heat loss. I also agree that just opening the windows once a day would be pretty effective.

It could also be that you really have a condensation problem, more than a humidity problem, from insufficient insulation. Condensation happens on items that are cooler than the room's air. When there's noticeable condensation on your windows, walls, and ceilings, it's worth checking out what your insulation is like, and maybe improving it. When the condensation is on windows, there could be air leaking through, or the window could be not built for winter (purely aluminum frames, for example, conduct heat very well, so in the winter the internal window pane/frame will be much cooler than other things in your room). The windows should be at least double-pane.

If you don't mind burning stuff indoors & have some extra money, a lot of people say wood stoves dehumidify the house.

  • Welcome to Sustainable Living! Nice first answer! – THelper Nov 17 '16 at 7:45
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    I second the suggestion for HRVs. My bathroom was absolutely plagued with mould when I moved into my current house, opening the window didn't help and just made the room freezing cold. Installing one of these has drastically reduced the humidity and keeps the room warm. – John M Dec 8 '16 at 19:51
  • Would second HRV - it is standard for new builds where I came from and ought to be included in building regulations for anywhere cold and/or damp. You can also get wall mounted units that do not require a ducting system, but of course they will only cover a limited area. – nsandersen Jan 23 '17 at 16:31
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Your best bet is to thoroughly ventilate the house by opening all windows at the same time. The resulting draft will quickly result in a complete exchange of air within a few minutes, so the "moist" air from your house or apartment will be replaced by the drier outside air (as pointed out by Chris H). The house itself won't lose heat. This is the way we ventilate in winter. The windows are kept closed except for the 5 minutes or so of thorough ventilation. I regard this step as a necessity at least once a day, otherwise the air gets rather pongy.

  • How will this not lose heat?! – Flyto Nov 15 '16 at 7:46
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    I think the idea is that only the air will lose heat, the actual building materials won't have time to give up their heat to the air. That's not to say I agree with the idea, but if you're going to be out long enough with the heating off that the house would cool down, it might be worth doing this just before you go out. @SimonW – Chris H Nov 15 '16 at 8:12
  • Ah, I see. Hmm. – Flyto Nov 15 '16 at 8:19
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For a sustainable solution, place dried bamboo in areas with the highest humidity. Bamboo naturally absorbs moisture, odors, bacteria, pollutants and allergens. If you can't grow bamboo in your climate, try Moso Natural for product ideas. And you recharge the bamboo by placing it in the sun for a couple hours.

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