If you live in a region with a cold winter climate, you may have wondered why you have to water your indoor plants more in winter than summer.  You may have also observed that your hands tend to dry out quicker in winter than summer.  Your throat and nose may also dry out in winter. 

This model simulates what happens inside your house when the temperature and dew point change outside.  You have control over the outdoor values by sliding the red colored portion of the two thermometers (one for temperature and one for dew point).  The relative humidity meter will instantly tell you the value for the outside.

As you change the values outside, your indoor environment is slower to change.  If the air is colder outside, your furnace will cycle on and off, keeping the house at approximately the value you set using the thermostat.

In addition to controlling the outside weather, you also control your indoor environment.  You can set the thermostat on your furnace.  Opening the door of your house (point and click on the box) allows outside air to mix into your home.  Close the door (point and click the box) turns on the furnace and starts to heat your house to your preset temperature.  Activities to the left can increase relative humidity, or can have no impact.  How can you increase the relative humidity without changing the air temperature?

To see how the outside air impacts your indoor environment:

  1. Set the outside dew point and  air temperature to -20F
  2. Set the thermostat to 75F
  3. Open the door, and keep it open until the indoor temperature drops to 60F.  When the door is open the outside air is mixing with the indoor air.
  4. Close the door.

Explain why your home is so dry during winter?

In the lower right hand corner of the applet there is a list of things that may, or may not, increase the relative humidity in your house.  What are other methods to keep the relative humidity in your house at a comfortable level?


The Verner E. Suomi Virtual Museum development funded in part by the National Science Foundation Grant #EAR9809458.  Material presented is Copyrighted (C) 1999 by Steve Ackerman and Tom Whittaker.  If you have questions or comments, please let us know!