4 ms·

There is also a problem of comfortable humidity levels. If you just have open windows, it seems like you will have very dry air. There are modern solutions fo

There is also a problem of comfortable humidity levels. If you just have open windows, it seems like you will have very dry air. There are modern solutions for air exchanges that do retain some of the heat and moisture while allowing for fresh air to ventilate the indoor space. https://www.explainthatstuff.com/heat-recovery-ventilation.html https://www.explainthatstuff.com/heat-recovery-ventilation.h...

Madmallard 5y ago
? If your windows are open you will trend toward outside weather. If you’re in a dry climate then yeah it’ll be dryer but the reverse is also true. Outside air is far better than inside nearly everywhere in the world
- newaccount74 5y ago
  Cold air can hold a lot less water vapor than warm air. If you open the window when it's cold outside, then the air will become very dry as it heats up. So even if you have 80% humidity outside on a cold winters day, once that air gets inside and heats up to room temperature it's going to be like 20% humidity.
  - nitrogen 5y ago
    Indeed, even in San Francisco I measured indoor humidity as low as 18% before I got a humidifier, and dryer+colder places (e.g. Salt Lake City) could be even lower inside. Humidity below 40-50% at indoor temperatures has noticeable negative effects for me. As other comments have mentioned, in the long run for maximum health and maximum energy efficiency we really need to design our buildings to be air tight, with energy-recovering ventilation systems and humidity control.
  - Izkata 5y ago
    That happens even if you don't open your windows, since buildings aren't perfectly sealed.
    - dredmorbius 5y ago
      It also depends greatly on how well your structure is insulated and where (or whether) vapour barriers exist. Vapour condenses against cold surfaces. This is why in winter poorly-glazed (e.g., single-glazed) windows "steam" up (really: condense), or frost over. Similarly water will condense against exterior walls, and may lead to degraded sheetrock (newer construction) or plaster (in older buildings), or rot. Where walls are insulated, a vapour barrier _before_ the insulation can lead to condensation inside the wall, again, against the exterior (cold) surface. The result is that even if the interior is humidified, moisture is "sucked out" by the exterior cold. (More accurately: vapour condenses against cold surfaces.) In summer, the problem is reversed, with warm humid exterior air condensing on surfaces cooled by interior air conditioning --- the outside of windows, or again, inside walls. Interiors can see higher relative humidity than the outside, and dehumidifiers may be needed.
- PeterisP 5y ago
  For humidity, the key issue is that relative humidity matters for us and that is temperature dependent. For example, if outside air has 100% humidity, then it effectively can't absorb more (e.g. evaporation of sweat) and would make things moist, but at -5 degrees Celsius, which I have now outside my window, that's only 2.46 g of water per kg of air - and if that exact air flows inside and gets heated to room temperature then it would suddenly have only ~17% humidity and would gladly absorb moisture from wherever possible e.g. my throat or skin; and any air going outside would remove more water vapor than the incoming air can possibly replace. There are ways around that (ventilation systems that exchange temperature and also retain moisture), but they need to be installed at some expense, you won't get that by opening a window.
  - chillwaves 5y ago
    I appreciate your detailed rundown. This kind of stuff is not intuitive to me.
GhettoComputers 5y ago
Dry air is a problem with any heating, but for those who are interested in a solution that currently exists (it’s a bit wasteful), is curious why they get too hot, or wants an easy solution without a new HVAC installation it’s very simple. Our radiator had a pan for water over the heater to keep humidity comfortable we’d refill.

Madmallard 5y ago

? If your windows are open you will trend toward outside weather. If you’re in a dry climate then yeah it’ll be dryer but the reverse is also true. Outside air is far better than inside nearly everywhere in the world

newaccount74 5y ago
Cold air can hold a lot less water vapor than warm air. If you open the window when it's cold outside, then the air will become very dry as it heats up. So even if you have 80% humidity outside on a cold winters day, once that air gets inside and heats up to room temperature it's going to be like 20% humidity.
- nitrogen 5y ago
  Indeed, even in San Francisco I measured indoor humidity as low as 18% before I got a humidifier, and dryer+colder places (e.g. Salt Lake City) could be even lower inside. Humidity below 40-50% at indoor temperatures has noticeable negative effects for me. As other comments have mentioned, in the long run for maximum health and maximum energy efficiency we really need to design our buildings to be air tight, with energy-recovering ventilation systems and humidity control.
- Izkata 5y ago
  That happens even if you don't open your windows, since buildings aren't perfectly sealed.
  - dredmorbius 5y ago
    It also depends greatly on how well your structure is insulated and where (or whether) vapour barriers exist. Vapour condenses against cold surfaces. This is why in winter poorly-glazed (e.g., single-glazed) windows "steam" up (really: condense), or frost over. Similarly water will condense against exterior walls, and may lead to degraded sheetrock (newer construction) or plaster (in older buildings), or rot. Where walls are insulated, a vapour barrier _before_ the insulation can lead to condensation inside the wall, again, against the exterior (cold) surface. The result is that even if the interior is humidified, moisture is "sucked out" by the exterior cold. (More accurately: vapour condenses against cold surfaces.) In summer, the problem is reversed, with warm humid exterior air condensing on surfaces cooled by interior air conditioning --- the outside of windows, or again, inside walls. Interiors can see higher relative humidity than the outside, and dehumidifiers may be needed.
PeterisP 5y ago
For humidity, the key issue is that relative humidity matters for us and that is temperature dependent. For example, if outside air has 100% humidity, then it effectively can't absorb more (e.g. evaporation of sweat) and would make things moist, but at -5 degrees Celsius, which I have now outside my window, that's only 2.46 g of water per kg of air - and if that exact air flows inside and gets heated to room temperature then it would suddenly have only ~17% humidity and would gladly absorb moisture from wherever possible e.g. my throat or skin; and any air going outside would remove more water vapor than the incoming air can possibly replace. There are ways around that (ventilation systems that exchange temperature and also retain moisture), but they need to be installed at some expense, you won't get that by opening a window.
- chillwaves 5y ago
  I appreciate your detailed rundown. This kind of stuff is not intuitive to me.

GhettoComputers 5y ago

Dry air is a problem with any heating, but for those who are interested in a solution that currently exists (it’s a bit wasteful), is curious why they get too hot, or wants an easy solution without a new HVAC installation it’s very simple. Our radiator had a pan for water over the heater to keep humidity comfortable we’d refill.