Here in the Tennessee Valley, we’re used to sticky, humid summer weather. But lately we had a stretch of hot, dry weather. Over this past winter, we had some very cold and dry weather, along with our usual rainy 40F days.
All these changes in outdoor humidity affect the humidity levels inside of our homes, and that affects our comfort too. Let’s take a look at how and why humidity affects our comfort in both the warmer and colder months of the year.
See Also: Humidity Control
Sensible Heat vs. Latent Heat
Did you know that there are two kinds of heat in your home? Your air conditioner is designed to remove both of those kinds of heat?
Sensible heat is the basic air temperature. It’s what your thermostat or any other thermometer measures, and most of the time, it’s what we mean when we just use the word heat.
Latent heat, on the other hand, is the heat that’s carried by the humidity in the air. You see, it takes heat energy to change water from liquid to gas. When the water changes to gas (i.e. water vapor or steam), it carries that heat energy with it.
Your air conditioner unit is designed to lower the sensible heat of the air in your home, but it also reduces the latent heat. It does this by causing the water vapor in the air to condense on the coils, removing the humidity from the air.
See Also: Heat and Air Systems
Humidity in the Summer
On hot, humid days, staying comfortable indoors involves regulating both the temperature and the humidity level. This means both the sensible and the latent heat. If the thermostat is set to what should be a comfortable level but the humidity stays high, it will feel too warm.
Why does higher humidity make warm temperatures feel hotter? First, there’s the latent heat being carried by the humidity. That heat isn’t measured by the thermometer in your average thermostat.
However, there are thermostats available that can measure the humidity in the air and adjust your HVAC system accordingly. It can do this by running your air conditioner for longer periods until the humidity is reduced to acceptable level.
Our Natural Defense
Of course, the other reason that warm, humid air feels hotter than warm, dry air has to do with the human body’s own internal cooling system. When we get too warm, our bodies produce sweat.
When that sweat evaporates into the air, it takes some of our body heat away with it. The problem is that the more humid the air, the harder it is for our sweat to evaporate. Essentially, the air is already “full” of water, so it can’t take more away.
On hot, dry days—which we do occasionally get in the South!—we feel cooler because our sweat is evaporating very quickly. It feels better, but it can be very easy to get dehydrated under those conditions because you may be sweating quite a bit without realizing it.
This is important to keep in mind when you’re spending summer days indoors with the air conditioner running. If the air conditioner is reducing the indoor humidity too much, you could end up with problems such as dry skin, sinus irritation, and nose bleeds.
Again, a thermostat that measures and regulates the humidity can help to prevent these problems.
See Also: Common Summer HVAC Problems
Humidity in the Winter
We generally associate the winter months with lower humidity, but here in the Tennessee Valley, we actually get some high humidity weather in the winter as well—those grey, rainy 40F days that can feel even more miserable than below-freezing temps.
In cold weather, humidity seems to have the opposite effect that it has in warm weather. In other words, higher humidity makes warm temperatures feel hotter, but it makes cold temperatures feel colder!
This is actually a kind of controversial phenomenon. There’s no settled scientific research that has found that more humid air makes you measurably colder. And yet, people generally agree cold, wet days feel colder than cold, dry days.
One possible explanation for this change in the perceived temperature is that the water vapor in the air soaks up body heat more easily than the air itself does. This means that more humid cold air will transfer your heat away faster, just like you get cold faster in wet clothes than in dry ones.
When it comes to indoor comfort, high humidity in the winter can make people feel colder and clammy. It’s also bad for the home itself, as condensation on the windows and other surfaces can lead to water damage and mold.
A more common winter problem is indoor humidity that’s too low. This is thanks to a combination of dry outdoor air and furnaces that dry the air even more. It can lead to discomfort in the form of nose bleeds, dry skin, and sinus irritation, as well as problems like static electricity and the cracking of wood floors and furniture.
Today, we have thermostats that can measure and regulate humidity, especially when paired with whole-house dehumidifiers (and humidifiers, where needed). And that can make a big difference for indoor comfort!