RELATIVE HUMIDITY: Warm air can possess more water vapor (moisture) than cold air, so with the same amount of absolute/specific humidity, air will have a HIGHER relative humidity if the air is cooler, and a LOWER relative humidity if the air is warmer.
Because air can only hold a particular amount of water vapour at different air temperatures. For example, warmer air can hold more water vapour – so it's often more humid.
It is correct, air conditioners can achieve a small amount of dehumidification while operating in cooling mode. They will remove moisture from the room where the room temperature is more than 2°C above the cooling mode set point.
Warmer air has more capacity to hold water vapor without saturating than colder air. Simply heating up that colder air causes the relative humidity to drop, because the water vapor capacity increases. That's why indoor humidity drops so low in cold winter weather if you not add moisture to the air.
Set the thermostat to a consistent temperature, even at 78°F, to keep humidity levels in check. Invest in a dehumidifier. Dehumidifiers are designed to extract excess moisture from the air. Place one in areas like bathrooms, basements, or laundry rooms for best results.
High humidity can cause problems in your home if relative humidity regularly exceeds 60%.
You already know that air conditioners cool off your home, but you may not realize that it also reduces the humidity in your home as well.
While there's no set humidity threshold above which general comfort level begins to deteriorate, NOAA typically considers relative humidity (RH) levels of 50% or more, and dewpoints (a more direct measure of humidity) above 65 F (18 C) to be uncomfortably high.
In short, ideal humidity levels in the winter months are almost always between 30-50%. Maintaining this range will help prevent dry skin, respiratory problems and even damage to wood furniture.
Ideally, you want to keep your home's humidity between 40% and 60%.
RELATIVE HUMIDITY:
Warm air can possess more water vapor (moisture) than cold air, so with the same amount of absolute/specific humidity, air will have a HIGHER relative humidity if the air is cooler, and a LOWER relative humidity if the air is warmer.
Dry mode is a setting on some air conditioning units that can help you reduce the humidity levels in your home. You may see it listed on the thermostat near the settings you're more familiar with, like “cool,” “heat,” and “auto.”
Energy Efficiency: To enhance energy efficiency while maintaining comfort, consider using the dry setting during times when the temperature is tolerable but humidity is high. Then, when the temperature rises, switch to the cooling mode for short bursts to prevent the room from becoming excessively warm.
Best Humidity for Sleeping
The best relative humidity for sleeping and other indoor activities has been debated. According to the Environmental Protection Agency, the best indoor relative humidity falls between 30% and 50%, and it should never exceed 60%. Other studies suggest 40% to 60% is a better range.
Hot air expands, and rises; cooled air contracts – gets denser – and sinks; and the ability of the air to hold water depends on its temperature. A given volume of air at 20°C (68°F) can hold twice the amount of water vapor than at 10°C (50°F).
Mold needs 55% or higher humidity in order to grow. Also, remember that reducing humidity below 30% isn't a good idea, either. This can cause health problems, making your eyes nose and skin dry, and exasperate lung and skin conditions.
When the house humidity level rises above 60%, it's considered high. High indoor humidity levels are common during summer, particularly in regions like the South that experience high outdoor humidity. When the air in your home is too humid, it poses serious health risks for you and your family.
According to the Consumer Product Safety Commission, a humidity level between 30–50 percent is ideal. The Environmental Protection Agency (EPA) expands that just a bit and recommends 30–60 percent humidity levels.
Appropriate Ventilation
Ensure your house has enough airflow by opening doors and windows to allow a cross-breeze, installing ceiling fans, or employing exhaust fans in bathrooms and kitchens to reduce dampness. This maintains ideal humidity levels by letting damp air escape and allowing fresh air to flow.
If there is a reading of 100%, it means that the air is 100% saturated with water vapor. It is incapable of holding any more water vapor. To explain it even further, if the air is at 100% humidity, it is not going to allow for sweat to evaporate into the air. This makes it feel as though it is hotter than it really is.
Use dehumidifiers and air conditioners, especially in hot, humid climates, to reduce moisture in the air, but be sure that the appliances themselves don't become sources of biological pollutants. Raise the temperature of cold surfaces where moisture condenses. Use insulation or storm windows.
Ceiling fans can be extremely beneficial in reducing humidity in a home because they are able to keep air circulating across an entire room and from the top down. Even a fan spinning at a low speed can help drastically with air circulation and lowering humidity.
If you keep the fan set to ON, the moisture will continue to be blown back inside. Setting it to AUTO allows the AC to shut off between cooling cycles. The condensation on the coils can then drain properly, rather than contribute to the humidity level inside your home.
While air purifiers do not remove moisture from the air, the movement of air can increase evaporation from surfaces in a room–including your skin and mucous membranes. This increased evaporation can make the air feel drier than it is.