You must be wondering why the concept of “hot air rises and cold air sinks” should concern you outside your physics classroom. This scientific phenomenon, also known as convection current, defines how your home is heated or cooled.
From warm spots around a heater to a cold floor near a window, the idea of hot air rising and cold air sinking can help explain all your home temperature worries.
Air leakages are the leading cause of why most homeowners fail to maintain their ideal home temperature. To make your home climate perfect, you need to understand how and why air exchange takes place. It’ll help you prepare your home for every weather and be free of all temperature-related worries!
Let’s understand this phenomenon with the help of real-life scenarios below and how it can be used to maintain the best home climate.
Why Does Hot Air Rise and Cold Air Sink?
While birds have wings and nature’s gift of flight, and airplanes are coupled with strong engines, it’s quite amazing to see a hot air balloon rising in the sky!
Yes, hot air rises – but to say that it’s the heat’s natural state to want to rise would be wrong. It can move in any direction. Basically, heat travels from an area of higher temperature to a lower temperature.
In scientific terms, this is known as the law of thermodynamics. According to the second law of thermodynamics, heat transfer can occur through convection, conduction, and radiation.
What drives the movement of hot air is the temperature difference. Since this isn’t a science lecture, we’ll keep things simple and easy to understand.
Heat Moves Towards Cold
Let’s take an instance from your normal routine. The temperature is 100 degrees and unbearable without air conditioning. You turn on your AC, and the next thing you do is close your windows.
Now, have you ever taken a minute to think about why you do that? Because heat follows cold!
If you’re running your air conditioner at 78 degrees but forget to close your windows, your room will never reach the desired temperature. The reason being, since it’s hot outside and there is cold air inside, heat will constantly move in through your window. The process won’t stop until a state of equilibrium (i.e., the same temperature both inside and outside) is achieved.
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Cold Air Sinks
On a breezy autumn day, you’re tempted to open your windows to improve ventilation and let the fresh cool air inside your home. If you own a multi-story home, then you must’ve noticed that the upper story feels much hotter than the downstairs.
This is because cold air sinks. Cooler air is denser, hence heavier since the molecule bonds absorb lesser energy than hot air. That is why cold air stays closer to the surface.
This brings us to the question: if cold air sinks, why does it get colder on higher altitudes? While it is true that heat rises at all altitudes, other factors also come into play.
For instance, the earth radiates heat, which is re-radiated by clouds hence increasing temperature. Less of this phenomenon can take place at higher altitudes, resulting in colder temperatures. You can learn more about it here.
How Hot Air Rising and Cold Air Sinking Affects Your Home Climate?
The air exchange between inside and outside air is driven by two forces. One is commonly known as the chimney effect or the stack effect. As hot air rises, it moves outside to the top of your home, and the colder outside air is drawn in from the bottom through gaps, leaks, and windows, etc.
The other factor is the negative pressure created by wind. When the wind blows, greater pressure is created on one side of your home than the other. As a result, outside air is pushed inside through cracks and gaps.
All of these things lead to an uneven temperature and a challenge to maintain your ideal home temperature. But with some basic HVAC knowledge and some tips and tricks, you can overcome this issue in no time!
1. Warmer Second Story in Summer
If you live in a multi-story home, you must be aware of the temperature difference between the upper and lower floors.
The primary reason why upper home levels are hot is the rising hot air. If, for instance, your kitchen is situated downstairs or near the stairs, hot air travels upstairs throughout the day. As a result, the upper story feels much warmer, while your basement may be very nice and cool.
Another reason for higher temperatures on upper floors is the direct sunlight falling on your house. The heat is absorbed by the walls and the roof and is transferred to the rest of your home.
You can solve this problem by properly insulating your attic to minimize the effect of hot rays. Moreover, you can work to increase airflow to the second floor to maintain a perfect atmosphere. Zoning is one effective method to reach the preferred temperature by circulating the air through the house. If your AC is not cooling upstairs, then read this article for potential problems and what you can do about it.
2. Air Leaks Through Cracks and Crevices
Air leaks are a common problem that every homeowner faces. These leakages not only disrupt your comfort but also increase your air conditioning costs.
They affect your home climate in two ways: When outside air leaks inside your home, it is referred to as infiltration. On the other hand, the air inside your home leaking outside is called exfiltration.
During summers, you introduce cold air inside your home through air conditioning, but the outside air is still warm. In the case of air drafts, air exchange takes place between outdoor and indoor air, resulting in an uncomfortable atmosphere and high energy bills. Similarly, it becomes a challenge to retain heated air indoors during winter. This makes it difficult to cool/heat your home as needed.
Doors and windows are the most apparent culprits behind air leaks in your home. However, gaps, drafts, holes, broken weatherproofing sealings are some of the less obvious and hence neglected reasons leading to heat loss.
It is important to get your home inspected for any air leaks before the start of peak seasons. The next step should be caulking all the leaks and weatherstripping your windows and doors.
3. Fans Circulate Settled Air
Since hot air rises and cold air sinks, fans come in pretty handy to get the settled air moving around your home.
In summers, run your fans in the counterclockwise direction. Even though fans do not cool a room, they do a better job of increasing airflow when coupled with an air conditioner. Since cooled air settles closer to the floor, running a fan would create a cool breezy effect all around your room. This even helps you set your thermostat a couple degrees higher, hence saving energy.
While fans are popular in summers, you may be surprised to know that they can be pretty useful in winters too. You just have to change their direction to clockwise for the colder months. As by now you know, hot air introduced by your heating system will rise, it’ll stay closer to the ceilings. Running your fan then helps to disperse it throughout your room.
4. Fireplaces Cause Heat Loss
Indoor fireplaces make a vintage statement while adding warmth to your interior. The aroma of burning wood and the sound of firewood crackling are unmatchable pleasures. But all this comes at a cost.
Even when not in use, fireplaces are responsible for around 90-95% of heat loss through conduction and infiltration. Since hot air rises, it escapes through the chimneys. Fireplace flues (the passageway inside your chimney) are a major source of air leaks. The flues are usually made of metal, and extreme temperature changes can cause cracks, leading to heat loss.
Inflatable chimney balloons are an effective way to prevent heat loss through flues. They fit below the chimney hole and block air inside your home from escaping outside.
5. Single-Hose Portable ACs Create Negative Pressure
Single-hose portable air conditioners are popular among homeowners because of their compact design and low prices.
One thing that many of you may not be aware of is that they are far less efficient. Single-hose portable ACs take in hot, humid air from your room and expel it outside. Since air is being constantly pushed out, it creates negative pressure. As an effect, warm air from gaps, cracks, doorways, and windows makes its way inside to substitute the missing air.
This not only makes your unit work harder but also makes it difficult to achieve your desired cooling effect.
Therefore, if you’re thinking of buying a portable air conditioner, a dual-hose one may be a better option. They are more efficient as one of the hoses acts as the air exhaust, and the other introduces cooled air.
Now you know everything there is to know about why hot air rises and cold air sinks. You can use this knowledge to make a few changes in your house, and your home’s temperature will be in your control!
Bonus Tip: Use smart thermostats or smart AC controllers to automate your air conditioning needs. These devices offer advanced features like Comfy Mode, scheduling, zoning, and much more, making your life full of convenience.
Time to live smart!