Alongside news of record-breaking heat waves and summer storms, you may have seen a few headlines about a curious phenomenon known as corn sweat. As temperatures climb, the millions of acres of corn fields sprawling across the midwest are causing localized humidity spikes, exacerbating the already searing summer heat.
But, what exactly is corn sweat? Why is it making the air feel hotter? And how can understanding this complicated relationship help you find the most energy-efficient home upgrades for extreme heat that fit your climate?
Keep reading to learn more about corn sweat and the key to cutting your energy bill without sacrificing your comfort this summer.
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What is corn sweat?
All plants have a self-cooling process called transpiration. It's essentially the plant version of sweating. When it's hot out, leaves release water through the pores in their leaves. That water evaporates, taking the heat with it as it leaves the surface of the leaf.
While the process happens differently in humans, the cooling mechanics are the same. Water vapor carries heat away from the body, whether it's a plant body or a human one.
According to the U.S. Geological Survey, a one-acre corn field will "sweat" 3,000 or more gallons of water per day. Then, add to that the water evaporating from the regularly-irrigated soil as well.
Globally, the impact of corn sweat or any other plant transpiration is tiny. 90% of the water vapor in the air comes from oceans, rivers and lakes. Only the remaining 10% comes from trees and plants "sweating."
But those numbers are planet-wide averages. In a state like Iowa, which has about 13.5 million acres of corn, the impact of that transpiration adds up.
In the right conditions – or wrong ones, for anyone trying to stay cool – corn sweat can increase local humidity levels by as much as 40%, according to the National Geographic.
In effect, you can have pockets of high humidity right around corn fields, causing the heat index (how hot it feels) to soar compared to neighboring areas that aren't near the sweaty crop.
Corn sweat would actually be a good thing in a dry climate
The relationship between temperature and humidity is weird. In a dry climate, corn sweat – or transpiration from any plant – would have a welcome cooling effect.
Transpiration from a single tree can have the cooling effect of five standard air conditioners running continuously for 20 hours, according to the EPA.
Combine that with a tree's shade blocking the sun from bearing directly down on you or the ground and the impact can result in air that is up to nine degrees cooler under a tree compared to just outside it. Even those sweaty corn fields are likely cooling the air below them by as much as five degrees.
The problem is that increasing the humidity also increases the heat index. In a dry climate, that increase is far outweighed by the decrease in temperature.
On an 82 degree day with 40% humidity, for example, a 10% increase in humidity would raise the heat index to 83 degrees. That one-degree spike is significantly outweighed by the nine-degree drop in temperature underneath a tree.
In a humid climate, on the other hand, the cooling effect of transpiration can easily be outstripped by soaring humidity. Take that same 82 degree day but say the humidity is already at 75%. A 10% increase in humidity would result in a heat index of 90 degrees.
As temperature and humidity levels get higher, the cooling effect of transpiration is drowned out entirely. By the time temperatures hit the 90s, a relative humidity of 60% or more already makes it feel 10 degrees hotter than it is.
Even air conditioning struggles to cool a humid climate
The cooling effect of plant transpiration isn't the only thing that's drowned out by high humidity. Your air conditioning also works harder to make your home feel comfortable when it's battling high humidity as well as high heat. The reason is the heat index.
Without getting too much into the math, the heat index refers to the difference between the actual temperature and how hot it feels. Relative humidity of 50% or above will start to feel warmer than the actual temperature.
When temperatures are in the mid-80s or below, every 10% increase in relative humidity will raise the heat index one degree further above the actual temperature.
At higher temperatures, the heat index climbs even faster. By 90 degrees, a relative humidity of 50% will make it feel like 95 degrees and every 10% increase in relative humidity above that will add five or more degrees to the heat index.
If you've got your air conditioner running, the ability of your system to make 90 degree air feel like, say, 78 degrees will be influenced by humidity. If you're at 50% humidity, 90 degrees would feel like 95.
Simply removing moisture to reduce the humidity to 40% or lower would already be enough to shave five degrees off the heat index, helping you stay cool without air conditioning — or at least easing the workload for your HVAC system.
Save money by getting a dehumidifier to help your AC
If you live in a humid climate, getting a portable dehumidifier can end up saving you money and increasing your comfort at home. By reducing the humidity in your home, you could potentially crank up the thermostat a couple of degrees without noticing any difference in your comfort.
At more moderate temperatures, running a dehumidifier alone may be enough to get your home to a comfortable temperature.
While air conditioners do dry the air somewhat as part of the cooling process, they're not nearly as efficient as a dehumidifier. Your AC removes less moisture and uses up more power to do it than a portable dehumidifier would.
Pairing the two gives you precision control over the climate in your home. By keeping the indoor humidity below 50%, you can make sure the temperature on the thermostat matches the temperature that you feel.
More tips for combatting humidity in your home
Getting a dehumidifier is the sure-fire way to keep humidity levels in your home where you want them. But if you don't have one or you don't have enough of them to dehumidify every room in the house, here are some other easy weatherproofing projects and summer cooling tips for making your home less muggy:
- Open windows and doors to ventilate your home. For even better results, point a fan at your open windows or doors to push hot, humid air outside.
- Get a whole house fan to consistently pull hot, damp air out of your home.
- Dry surfaces promptly. After you shower, wipe down the walls and bathtub. After you do the dishes, wipe down the sink. These small habits can reduce the amount of water available to evaporate into the air, helping reduce overall humidity indoors.
- To keep humid outside air from seeping into your home, make sure your windows and doors are caulked and sealed.
- Add humidity-loving plants like orchids and snake plants. They can dehumidify the air around them by absorbing the water vapor for themselves. The effect here is small, but if you like plants and have the time to care for them, prioritizing moisture-hungry species like these will work in your favor.
Smart ways to beat the heat and cut energy costs
Understanding how factors like corn sweat and high humidity impact your home environment can help you take smarter steps to stay comfortable.
Investing in a dehumidifier, sealing air leaks and using ventilation tools effectively can reduce strain on your air conditioning system and lower energy bills. With the right upgrades, you can maintain a cooler, healthier home, even in the most extreme summer heat.
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