Quote:
Originally Posted by ehonour
Ton80 has it mostly right. His definition of dewpoint is correct.
However, a dewpoint number makes no sense at all unless you also know the actual temperature, because what matters is the difference between temperature and dew point. If the difference is zero, as in his example (i.e temp=60 deg and dp=60 deg), then you have water condensing on surfaces. In that condition, the relative humidity is 100%; the air is holding all the water it can possibly hold.
You can have temperature of 105 deg and dewpoint of 80 deg and still feel very dry, with the sweat rapidly evaporating from your skin. (RH of 46%) Or temp of 40 deg and dewpoint of 40 deg and feel oppressively humid. (RH of 100%)
What matters for comfort is relative humidity, not dewpoint.
Concerning the OP question, an indoor RH of over 70% is pretty high. It's not yet mold territory, but something's not right.
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This is not correct per the National Weather Service, but what would they know?
"Dew Point vs. Humidity
The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point the air cannot hold more water in the gas form. If the air were to be cooled even more, water vapor would have to come out of the atmosphere in the liquid form, usually as fog or precipitation.
The higher the dew point rises, the greater the amount of moisture in the air. This directly affects how "comfortable" it will feel outside. Many times, relative humidity can be misleading. For example, a temperature of 30 and a dew point of 30 will give you a relative humidity of 100%, but a temperature of 80 and a dew point of 60 produces a relative humidity of 50%. It would feel much more "humid" on the 80 degree day with 50% relative humidity than on the 30 degree day with a 100% relative humidity. This is because of the higher dew point.
So if you want a real judge of just how "dry" or "humid" it will feel outside, look at the dew point instead of the RH. The higher the dew point, the muggier it will feel.
General comfort levels USING DEW POINT that can be expected during the summer months:
less than or equal to 55: dry and comfortable
between 55 and 65: becoming "sticky" with muggy evenings
greater than or equal to 65: lots of moisture in the air, becoming oppressive"
Dew Point vs Humidity.