Indoor Weather

Everyone talks about the weather a lot during winter. Will it snow? When will we have a sunny day? All we can do about the weather outdoors is dress so we will be comfortable when we go outside. But we can do something about the indoor weather.

What is indoor weather? Indoor weather is the temperature and humidity in buildings. Winter is a good time of year to learn more about it.


In winter, the indoor temperature is kept above freezing by a furnace, a wood stove, or some other heat source. With a wood stove or fireplace, you control the temperature by making the fire larger or by letting it burn down. Furnaces have a thermostat that can be set to a certain temperature. When the room gets a degree or two cooler than what the thermostat is set for, the heat turns on and warms the room. When the room gets a degree or two warmer than what the thermostat is set for, the furnace turns off again. How does this work?

Inside a thermostat is a coil that is made of two different kinds of metal. Different metals expand at different rates as they are heated and contract at different rates as they cool off. As the two metals that make the coil cool, one side of the coil shrinks more than the other. This makes the coil tighten. When it tightens enough, it moves a small tube that has mercury in it. This makes the mercury flow towards one end of the tube to complete a circuit, turning the furnace on. As the room warms up, the metals expand again. The coil unwinds or loosens. When it unwinds enough, it moves the tube enough for the mercury to break the circuit and turn the furnace off again. How Stuff Works has a more complete explanation of how thermostats work at an adult reading level.

A thermostat controls the temperature at one spot. Other places in your house or school may not be at that same temperature. Go on a temperature hunt with a thermometer. Hunt for the coolest spot you can find indoors. Where is it? Why do you think this spot is so chilly? Is there anything that could be done to keep this spot from being this cool?


Humidity is the amount of water in the air. You probably remember summer days that were very hot and sticky. There was so much moisture in the air on those days that your own perspiration or sweat didn’t evaporate very well. When perspiration does evaporate, it cools your skin, making you more comfortable. If the humidity is too high, sweat doesn't evaporate easily and you stay feeling hot and sweaty. 

In winter, dryness or low humidity can be a problem indoors. Generally, warm air can hold more moisture than cold air can. In winter, the air outdoors is colder than the air indoors. Because it is cold, outside air holds less moisture than inside air can. Whenever we open a door, this cold air comes inside, and gets warmed up. The indoor air becomes very dry. Because of this, bath towels in winter dry very quickly after they have been used. Our hair dries quicker after a shower. We wake up in the morning feeling dry and thirsty. We might even get shocks from static electricity. Visit Science Made Simple to read more about static shocks. You can also read about static electricity at School for Champions.

How can you measure humidity? You can make your own sling psychrometer. A sling psychrometer uses two thermometers to measure relative humidity (how much moisture is in the air compared to how much moisture the air could hold at that temperature). One thermometer measures the air temperature. The other thermometer is wet. By swinging it around, the water evaporates and cools the thermometer. How much it cools tells you how dry the air is. The Miami Science Center has directions for making a sling psychrometer. The Old Farmers' Almanac does too.

Can you do anything about increasing the humidity indoors in the winter? There are commercial humidifiers that put more moisture into the air. Or you can use the old-fashioned method, put a pan of water out so that the water can evaporate. Raising the humidity indoors will make you feel warmer and might even help you keep from catching as many colds this winter. The lining of your nose is better at keeping out viruses if it does not get too dry.

Indoor weather is one part of winter you can do something about.
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