Think your thermostat is lying? Science explains why.
You’ve probably experienced moments when the number on your thermostat simply doesn’t gel with how you’re feeling. If it’s 74 degrees, why do you need the fuzziest socks and a Snuggie to avoid a chill? Or maybe you brace for battle with your mother-in-law whenever she comes over because she somehow always insists that your home feels like a sweat lodge.
As it turns out, it’s not necessarily that your thermostat is lying, or – sorry – that your MIL is wrong. It’s that the thermostat tells only one small part of a rather complex story.
When most of us talk about feeling hot or cold, we think we’re referring to the temperature. But the number on a thermometer is just one element of what the experts call “thermal comfort.” That term describes more holistically how satisfied an individual body feels within the climate of a given environment – and why. In addition to temperature, it takes into account factors such as humidity and air flow. There’s even research that suggests the colors of a room can affect how warm or cool it feels to various people.
In short, unlike a reading on a thermostat, thermal comfort is subjective, explains Shichao Liu, an assistant engineering professor at Worcester Polytechnic Institute who studies the interaction between buildings and their occupants: “It’s the interpretation and perception of our environment.”
So stop casting that accusatory side eye at your thermostat, and take a deeper look at the reasons we experience temperature differently. Humidity and air flow Think about the weather report. In addition to the temperature, it also tells you the heat index or wind chill, which gives you a better idea of how the weather will actually feel when you step outside. On an August day in D.C., 90 degrees might feel more like 103, thanks to the humidity. On a blustery December day, 40 degrees could bite like 32. These same dynamics also play out inside your home, just on a smaller scale.
Humidity measures the amount of water vapor in the air, which matters because sweating – your body’s best bet for cooling down – isn’t just about releasing perspiration, explains Matthew D. White, an associate professor of physiology at Simon Fraser University. For you to feel any relief, your sweat needs to be able to evaporate. If the air is already filled with water, there’s nowhere for your sweat to go. While some fancy thermostats measure humidity, many don’t, meaning yours probably is not filling you in on a key factor in your perception of the indoor environment.
While we don’t typically think of indoor air flow as a breeze – as we would if it was occurring outside – it affects our thermal comfort in much the same way that wind does.
Inside, of course, the airflow comes from fans or HVAC systems. The ways in which those circulate the air affect how you experience the temperature. “We want the air to go up when we want it to be warm in the house and it’s winter” because it makes the temperature across a building more uniform, says Jennifer Lather, an assistant professor of engineering at the University of Nebraska at Lincoln. This is because an upward flow keeps the air in a room circulating, and prevents the hottest air from simply rising to the ceiling and remaining there. On the other hand, when it’s hot it’ll probably feel better if air is pushing downward, so you can feel the relief of a breeze. (Both Lather and Liu are part of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, which generates research and standards for how the built environment can promote well-being.) How your home is built If your windows or doors aren’t well-insulated, cold air will seep into your home on frigid days and meet with the warmer air inside. This collision, explains Lather, “creates air movement,” leading to a changing climate in your home, just as the meeting of large masses of hot and cold air in the great outdoors causes extreme weather patterns. In your house, the clash creates a draft that can make you feel colder, even though your thermostat won’t necessarily reflect all this drama. (Windows also come into play on hot days, because they’re where the sun’s radiation enters your home, making you feel warmer.)
The materials used to build your home can also influence how warm or cold you feel because different materials hold heat differently. Wood, for instance, heats up faster than cement but retains heat for less time. Whether your thermostat can keep up with those changes depends on how fast the temperature fluctuates throughout the day, and how much sunlight hits your home.
The impact of colors It might sound a little out there, but it’s true: An evolving area of research in the world of thermal comfort shows that the color of a room or object may influence how we experience its temperature.
The concept, called the “hue-heat hypothesis,” asserts that cool colors, such as blue, can cause people to perceive cooler temperatures, and warmer tones like yellow or red can lead to a warmer perception. There is evidence to back this up, including a study that found different colored lights had an impact on how hot or cold airline passengers felt, and a 2016 study that found people held a hot object longer if it was blue and a cold object longer if it was red.
Whether a room is done up in a cool or warm color isn’t the only consideration. Another element rife for exploration is the relative light or darkness of the hue, says Lather. In a darker room, for instance, “you have this sense of coziness because you feel like you’re in a smaller space.”
Some us really do just ‘run’ hot or cold
You’ve probably heard people say they “run hot” or “run cold” – often leading to spats over the correct temperature to set the thermostat. “There are different perceptions of the same conditions,” says White, the physiologist, which is why some people start sweating or shivering before others.
One major factor in how you “run” is whether you’re used to hot or cold. If you’re accustomed to a freezing climate, you’ll be less tolerant of heat and likely to feel it more intensely than someone who grew up in Miami (and vice versa), though this can change over time.
Physiological components such as your metabolism (how much heat your organs generate) and your body’s fat content, which can affect the transfer of heat from inside your body to your skin, also come into play. And, of course, how much you’re moving and what you’re wearing will also affect your perception of thermal comfort – so don’t underestimate the value of keeping a throw blanket or two around.