6 ms·

The CDC has some recommendations on it (yes you can have mold tested to see if it's dangerous): https://www.cdc.gov/mold/stachy.htm https://www.cdc.gov/mold/st

by fyfy18 8y ago

The CDC has some recommendations on it (yes you can have mold tested to see if it's dangerous): https://www.cdc.gov/mold/stachy.htm https://www.cdc.gov/mold/stachy.htm I'm not really sure about keeping the humidity below 50% though. The UK and most of Northern Europe has rather high humidity in the winter. It commonly reaches 80-90 RH outside, so you'd have to heat your house to 25c/77F to bring the humidity below 50%.

toxik 8y ago
Northern Europe gets really cold, so while RH may be high, it’s not moist at all. People get dry skin in the winter.
- chupasaurus 8y ago
  Northern Scandinavia and west of Urals (I live here) have moist winters (70+% RH most of the time). Skin would dry anyway because water evaporation rate is proportional to a pressure (hence temperature) difference and convection makes a constant supply of fresh unsaturated air.
  - zaarn 8y ago
    Relative Humidity is relative to temperature. Cold air can simply hold less water overall, at 20C it can easily hold double as much water as it can at 0C. There being a pressure difference is nonsense, you can get the same air pressure in the winter as in summer (though it tends to go on the Low side more often). What you probably mean is the vapor pressure, ie the natural pressure the liquid wants to be at in a closed container, though while it is largely depdenent on temperature, it does so in a linear/positive way, so at lower temperature, water will evaporate less (otherwise ice would more easily sublimate). Once you go below zero a water content of a few grams can easily hit 100% RH which would barely manage 5% or less at 30C.
    - logfromblammo 8y ago
      I think the relevant pressures are the vapor pressure of liquid water, the atmospheric pressure, and the partial pressure of gaseous H2O at the gas-liquid interface. If you can blow dry air over its surface, you can evaporate liquid water (or sublimate water ice) even when the relative humidity is 100%. You can think of air as a gaseous solution, and its water vapor content like table salt in aqueous solution. Temperature affects the solubility, and if the solution is saturated, no more can dissolve. You can still dissolve salt crystals sitting in a saturated cold saltwater solution by squirting warm freshwater onto the bottom of the container. If that then mixes with the rest of the solution, and everything cools down again, that dissolved salt can then precipitate out somewhere else (like rain), or form a suspension of tiny crystals (like fog or clouds). The solubility of H2O vapor in atmospheric gas increases with temperature. But you can also do something with a gaseous solvent that you can't easily do with a liquid solvent, which is to change the pressure. Higher pressure lowers the solubility of water in air, but to a far lesser extent than a decrease in temperature. Even though the vapor pressure is dependent only on temperature, evaporation occurs whenever the vapor pressure exceeds the partial pressure of H2O at the interface. Increasing the overall air pressure also increases the partial pressure of H2O vapor by a proportional amount, so inhibits further evaporation. But water vapor is also less dense than N2, O2, and most other atmospheric gases, so the means of measuring pressures gets complicated. When you involve wind, and stratified airflows, it gets even more complicated. The air blowing across water or water ice could have been previously warmed by the ground just enough to evaporate more water, then get pushed higher by an angled snowbank into colder, saturated air, and it will then dump the excess water as small ice crystals. A solid block of ice can then become "rotten" as a snowdrift forms downwind of it. The overall average temperature may say that ice should stay frozen, but the wind can still carry a tiny bit of water vapor at a time, thanks to local fluctuations, and with enough volume of air to move it, that ice will drift.
roel_v 8y ago
"The UK and most of Northern Europe has rather high humidity in the winter." Indoors? No, not at all. In the winter the temperature in my house/office is 21-22C and 17 at the lowest at night, and I have to run a humidifier 24/7 to keep the humidity over 30% (otherwise the wooding floors shrink too much).
- zimpenfish 8y ago
  (anecdata but...) Currently in the bedroom (thanks Netatmo) it's 17.8° and 69% humidity (with one of the three windows open about 0.5"). That compares to 14.0° and 78% on the balcony. Looking at the graphs, 50% is the lowest indoor humidity over the last month.
  - roel_v 8y ago
    Yes, bedrooms have the windows open more often, and usually less/no heating. How many hours a day do you have the windows open? Is there a heating source on or nearby? If you close the window, you'll see RH drop quite fast (in most houses). I'm going to try this same experiment tomorrow, I'm quite interested to know. Still - mold in houses is not a problem in houses in Western/Northern Europe, except for the most pathological cases (for example, mold scores you iirc 2 points in Belgium on the 'uninhabitable property' test, where 9 gets your building declared unfit for living in. Having small holes in the roof or small cracks in the walls (still structural defects) gets you 3. That's how unusual mold is around here. OTOH when I lived in New Zealand, mold was met with 'eh, there's bleach in isle 5 at Countdown, just wipe it down.'. I was like 'wut?'.
    - zimpenfish 8y ago
      > If you close the window, you'll see RH drop quite fast (in most houses). Alas, it does not, but that's possibly because other windows are open around the place and there's relatively good airflow. > I'm going to try this same experiment tomorrow, I'm quite interested to know. I'll see how it goes tomorrow with the window closed and various doors closed to minimise the effect of the other windows.
- deleted 8y ago
adrianN 8y ago
Heating your home to like 25 degrees and opening the windows every six hours is actually required in some tenancy agreements.
- Tharkun 8y ago
  What? That's an insanely uncomfortable indoor temperature. Anything over 20 and I'm uncomfortable.
  - Foobar8568 8y ago
    In Switzerland, they have a tendancy to overheat, now I am used to a constant 25°C over the year. It's actually quiet comfortable.
  - adrianN 8y ago
    I believe the idea is that the landlord is never responsible for mold problems since no sane tenant could comply with those rules.
  - zaarn 8y ago
    It's a matter of getting used to it, really. Once you've been at a temperature for a while, it gets easier.
  - Raphmedia 8y ago
    What is the humidity level in your house? 25ºC should be comfortable for an healthy individuals if the hair is not heavy with humidity.
    - Raphmedia 8y ago
      Bwahahahahaha... air
Moru 8y ago
We do have cold winters but that does not mean we have high humidity indoors. Relative humidity means the water contents of the air at 0 degrees is very very low. The higher temperature, the more moisture the air can hold. So when you heat up the air the same amount of water shares a much lower percentage of what the air can hold. In winter the hygrometer is showing 100% moisture outdoors (because ours can't measure below zero degrees C). When that air is heated up indoors, it holds about 20% of what it can hold [0], most likely thanks to warm water taps, us breathing and other moisture sources. This is why many people run their humidifiers so they can at least have 30-40% in winter. Less dry, cracked skin and nose bleed. [0] https://en.wikipedia.org/wiki/File:Relative_Humidity.png https://en.wikipedia.org/wiki/File:Relative_Humidity.png
- fyfy18 8y ago
  Yes, but that's my point. Where I'm currently living (UK, south coast) it's 15C at 77% RH outside, so to get below 50% RH inside the temperature needs to be at least 22C (which it isn't). It's not uncommon for the humidity to get up to 80-90% RH when it rains, and the temperature doesn't drop much. When it gets to the cold part of winter it's obviously easier, but this time of year it's hard to get it below 50% RH inside just by controlling the temperature.

by fyfy18 8y ago

toxik 8y ago

Northern Europe gets really cold, so while RH may be high, it’s not moist at all. People get dry skin in the winter.

chupasaurus 8y ago
Northern Scandinavia and west of Urals (I live here) have moist winters (70+% RH most of the time). Skin would dry anyway because water evaporation rate is proportional to a pressure (hence temperature) difference and convection makes a constant supply of fresh unsaturated air.
- zaarn 8y ago
  Relative Humidity is relative to temperature. Cold air can simply hold less water overall, at 20C it can easily hold double as much water as it can at 0C. There being a pressure difference is nonsense, you can get the same air pressure in the winter as in summer (though it tends to go on the Low side more often). What you probably mean is the vapor pressure, ie the natural pressure the liquid wants to be at in a closed container, though while it is largely depdenent on temperature, it does so in a linear/positive way, so at lower temperature, water will evaporate less (otherwise ice would more easily sublimate). Once you go below zero a water content of a few grams can easily hit 100% RH which would barely manage 5% or less at 30C.
  - logfromblammo 8y ago
    I think the relevant pressures are the vapor pressure of liquid water, the atmospheric pressure, and the partial pressure of gaseous H2O at the gas-liquid interface. If you can blow dry air over its surface, you can evaporate liquid water (or sublimate water ice) even when the relative humidity is 100%. You can think of air as a gaseous solution, and its water vapor content like table salt in aqueous solution. Temperature affects the solubility, and if the solution is saturated, no more can dissolve. You can still dissolve salt crystals sitting in a saturated cold saltwater solution by squirting warm freshwater onto the bottom of the container. If that then mixes with the rest of the solution, and everything cools down again, that dissolved salt can then precipitate out somewhere else (like rain), or form a suspension of tiny crystals (like fog or clouds). The solubility of H2O vapor in atmospheric gas increases with temperature. But you can also do something with a gaseous solvent that you can't easily do with a liquid solvent, which is to change the pressure. Higher pressure lowers the solubility of water in air, but to a far lesser extent than a decrease in temperature. Even though the vapor pressure is dependent only on temperature, evaporation occurs whenever the vapor pressure exceeds the partial pressure of H2O at the interface. Increasing the overall air pressure also increases the partial pressure of H2O vapor by a proportional amount, so inhibits further evaporation. But water vapor is also less dense than N2, O2, and most other atmospheric gases, so the means of measuring pressures gets complicated. When you involve wind, and stratified airflows, it gets even more complicated. The air blowing across water or water ice could have been previously warmed by the ground just enough to evaporate more water, then get pushed higher by an angled snowbank into colder, saturated air, and it will then dump the excess water as small ice crystals. A solid block of ice can then become "rotten" as a snowdrift forms downwind of it. The overall average temperature may say that ice should stay frozen, but the wind can still carry a tiny bit of water vapor at a time, thanks to local fluctuations, and with enough volume of air to move it, that ice will drift.

roel_v 8y ago

"The UK and most of Northern Europe has rather high humidity in the winter." Indoors? No, not at all. In the winter the temperature in my house/office is 21-22C and 17 at the lowest at night, and I have to run a humidifier 24/7 to keep the humidity over 30% (otherwise the wooding floors shrink too much).

zimpenfish 8y ago
(anecdata but...) Currently in the bedroom (thanks Netatmo) it's 17.8° and 69% humidity (with one of the three windows open about 0.5"). That compares to 14.0° and 78% on the balcony. Looking at the graphs, 50% is the lowest indoor humidity over the last month.
- roel_v 8y ago
  Yes, bedrooms have the windows open more often, and usually less/no heating. How many hours a day do you have the windows open? Is there a heating source on or nearby? If you close the window, you'll see RH drop quite fast (in most houses). I'm going to try this same experiment tomorrow, I'm quite interested to know. Still - mold in houses is not a problem in houses in Western/Northern Europe, except for the most pathological cases (for example, mold scores you iirc 2 points in Belgium on the 'uninhabitable property' test, where 9 gets your building declared unfit for living in. Having small holes in the roof or small cracks in the walls (still structural defects) gets you 3. That's how unusual mold is around here. OTOH when I lived in New Zealand, mold was met with 'eh, there's bleach in isle 5 at Countdown, just wipe it down.'. I was like 'wut?'.
  - zimpenfish 8y ago
    > If you close the window, you'll see RH drop quite fast (in most houses). Alas, it does not, but that's possibly because other windows are open around the place and there's relatively good airflow. > I'm going to try this same experiment tomorrow, I'm quite interested to know. I'll see how it goes tomorrow with the window closed and various doors closed to minimise the effect of the other windows.
deleted 8y ago

adrianN 8y ago

Heating your home to like 25 degrees and opening the windows every six hours is actually required in some tenancy agreements.

Tharkun 8y ago
What? That's an insanely uncomfortable indoor temperature. Anything over 20 and I'm uncomfortable.
- Foobar8568 8y ago
  In Switzerland, they have a tendancy to overheat, now I am used to a constant 25°C over the year. It's actually quiet comfortable.
- adrianN 8y ago
  I believe the idea is that the landlord is never responsible for mold problems since no sane tenant could comply with those rules.
- zaarn 8y ago
  It's a matter of getting used to it, really. Once you've been at a temperature for a while, it gets easier.
- Raphmedia 8y ago
  What is the humidity level in your house? 25ºC should be comfortable for an healthy individuals if the hair is not heavy with humidity.
  - Raphmedia 8y ago
    Bwahahahahaha... air

Moru 8y ago

We do have cold winters but that does not mean we have high humidity indoors. Relative humidity means the water contents of the air at 0 degrees is very very low. The higher temperature, the more moisture the air can hold. So when you heat up the air the same amount of water shares a much lower percentage of what the air can hold. In winter the hygrometer is showing 100% moisture outdoors (because ours can't measure below zero degrees C). When that air is heated up indoors, it holds about 20% of what it can hold [0], most likely thanks to warm water taps, us breathing and other moisture sources. This is why many people run their humidifiers so they can at least have 30-40% in winter. Less dry, cracked skin and nose bleed. [0] https://en.wikipedia.org/wiki/File:Relative_Humidity.png https://en.wikipedia.org/wiki/File:Relative_Humidity.png

fyfy18 8y ago
Yes, but that's my point. Where I'm currently living (UK, south coast) it's 15C at 77% RH outside, so to get below 50% RH inside the temperature needs to be at least 22C (which it isn't). It's not uncommon for the humidity to get up to 80-90% RH when it rains, and the temperature doesn't drop much. When it gets to the cold part of winter it's obviously easier, but this time of year it's hard to get it below 50% RH inside just by controlling the temperature.