Eliminating the MoistureIn older homes with leaks in every window, door and fixture the humidity drops in the winter as the outside air temperature drops. Since the house is getting so many air changes from its many drafts, the cold air coming in, when warmed has a very low relative humidity. However in a new home, there is quite a different situation. New homes are sealed tight as a drum. This makes them much cheaper to heat and cool, but brings along the problem of higher humidity in winter. Breathing, cooking and bathing all add a significant amount of moisture to the air. Without those drafts carrying the moisture outside, the humidity in the house rises. This can cause problems in the walls and attic of the house as well as making it rain on even the best thermal windows. In the walls and attics, when the moist air makes its way through the insulation and reaches the cold, it condenses, reducing the insulation's effectiveness and can cause dry rot in the wood.
VentilateTo eliminate the moisture, use those bathroom and kitchen fans during times when you are adding a lot of moisture to the air (as we said before). If you burn a kerosene heater unvented in your home, you will be adding a significant amount of moisture to the air. These should be vented to the outside if you have a moisture problem in your house.
To lower the humidity level, an air to air heat exchanger can be added to vent the house's air outside and bring in fresh air. By using the outgoing air to raise the temperature of the incoming air, they are somewhat more efficient than merely cracking a window and running your bathroom fan. They will bring in fresh air which is a healthy thing in itself.
Seal out the moistureA significant source of humidity for many homes is a crawlspace with a dirt floor. These should always be covered from wall to wall with plastic. 6 mil poly plastic can be bought in very wide rolls and laid out on the dirt floor weight down around the edges. All the seams should be over lapped and even taped. Where the plasitc meets the wall, to make and even tighter seal, you can use roofing tar to seal the plastic to the wall. Just paint a strip all the way around the wall with the tar and stick the plastic to it. This vapor barrier will eliminate a great deal of moisture coming into the house.
DehumidifiersEven in a relatively dry house, often the basement can be damp and moisture can cause growth of mold and mildew.. and that dank smell it causes. If a basement is cooler than the rest of the house and the outside in the summer, than its relatively humidity will be much higher. Therefore a dehumidifier should be run in the basement at least until it is warmer in the basement than the air outside.
Use the chart below to determine what size dehumidifier you should use for your basement.
Just as an oh-by-the-way, a dehumidifier will add noticable heat to the room it is in. This is due to the fact that it is not dumping the heat from the compressor and the condensing coils outside like an air conditioner does. So, though the humidity is dropping the temperature will be rising.
Heating the roomThe warmer a room is, the lower its relatively humidity, so if it is practical heating a room in winter will lower the humidity. This may be an appropriate fix for an unheated attic room.
Air ConditionersAir conditioners in addition to cooling the air, drop the humidity by removing a significant amount of water from the air. During the hot air conditioning times of the summer, it is more economical and practical to NOT open the windows at night even if it cools outside slightly. Leave the house closed up and don't bring the humid air inside. If you do, during the day, the air conditioner will be working that much harder to remove the heat and moisture from the air that was introduced during the night. There is a significant amount of moisture not just in the air, but absorbed by the furniture, wood etc in the house that will need to be removed to lower the humidity level in the house again. For comfort, a humid room will have to be much cooler than a dry room to have the same degree of comfort feel. So, consider this when it cools off a bit outside, if you will be running the A/C again tomorrow and it is still humid outside, don't open the windows.
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