We care about the temperature of the air in the room, while forgetting about the humidity, but heaters dry the air, which entails not the most pleasant effects is dryness of mucous membranes, respiratory and allergic diseases.
Normal is relative humidity in the interval 40-60 %. Basically, you may not feel that the humidity becomes smaller than the lower limit of normal in the first place to get a feel for the cut flowers and potted plants – they dry quickly, the leaves turn yellow and fall off.
Humidity may be measured by the hygrometer. It's not very expensive and easy to use device. But in order to establish normal if the humidity in the room you can do without it, with it in several ways.
Take an ordinary room thermometer, lock his testimony in this room. Wrap the tip of the thermometer with a damp cloth and leave it in the same room for 5-10 minutes. Calculate the relative humidity according to the formula derived from the proportion. It will be equal to the result of dividing the works of the second measurement temperature and 100% at the temperature of the first measurement.
There is one rather simple way to determine the humidity in the room. You need to fill a small glass with water and put in some time, e.g. overnight, in the refrigerator. In the morning remove and leave for 5 minutes in a room away from heaters and humidifiers.
Watch as the misted surface of the glass. If after 5 minutes the glass had time to dry, it means that the humidity in the room low. Uniform fogging of the glasses indicate normal humidity. But if it flowed a trickle of condensation, the humidity is high.
To combat the dry air by special devices-humidifiers, or just place it away from heat sources water containers.