The Science of Home Comfort
The Science of Home Comfort: Temperature, Humidity, Airflow, and Ventilation
Whole home comfort is about more than just temperature. You also need to account for ventilation, airflow, and humidity, all of which affect how you feel inside your home. Below, we review how these factors interact and things companies like John’s can do to ensure your home is always in the Goldilocks Zone.
What Does It Actually Mean to Feel Comfortable?
With temperatures well over 100°F in the summer, Mesa and Maricopa County are among the hottest places in the nation. With how hot it gets, no amount of AC should feel like it’s too much, right? But have you ever felt a day when your AC seems to run too cold? Maybe some rooms get far colder than others, resulting in uneven temperatures in your house. Often, the downstairs gets frigid while the upstairs stays warm.
Whole home comfort takes more than just temperature control. Factors like humidity, air movement, and ventilation also come into play. Your air conditioner might keep the heat at bay, but does it manage humidity well? In the winter, it’s easy for a furnace or heat pump to keep the temperatures above 65°F, but are you still comfortable when sitting by the window? These are the questions HVAC professionals have to answer when managing your home’s comfort.
The Four Ways Your Body Exchanges Heat With a Room
To understand how whole home comfort truly works, it helps to look at how the human body exchanges heat with its surroundings. Your body has to maintain a temperature of around 98.6°F. Since it’s constantly generating heat, that means rejecting heat out into the environment. If it does that too slowly, it could overheat. In Mesa, that often leads to heat exhaustion or heat stroke. On the other hand, if it loses heat too fast, hypothermia could occur.
To manage heat loss, your body uses a number of methods:
- Conduction: Conduction happens through direct contact with an object. If you touch a metal chair, for instance, your body heat will transfer into it. Overall, conduction accounts for very little heat transfer in homes.
- Convection: Your skin warms the thin layer of air directly around your body. When that air moves away, cooler air replaces it and can absorb more heat from your skin. This increases convective heat loss, which is why a fan can make you feel cooler even though it doesn’t actually lower the room temperature.
- Radiation: Your body also exchanges heat with nearby surfaces through radiant heat transfer. That’s why you can feel colder near a cold window in winter even when there’s no draft. The colder surface draws radiant heat from your body.
- Evaporation: As the air around you gets hotter, your body relies more heavily on sweat to release heat. When sweat evaporates from your skin, that process uses heat and helps cool your body. Dry air allows sweat to evaporate more readily, which is one reason Arizona’s low humidity can make high temperatures feel more tolerable than the same temperature in a humid climate.
Four Home Conditions That Affect Thermal Comfort
Your body’s methods of heat transfer are why things like the indoor dew point and radiant temperature are so important. The way your HVAC systems manage air and humidity can dramatically affect how your home feels. Some factors have no effect on the actual temperature but impact how your body feels. That’s referred to as thermal comfort. The factors that affect thermal comfort are shown below.
| Change | Temperature Effect | Humidity Effect | Airflow Effect | Comfort Result |
|---|---|---|---|---|
| Higher air speed | No actual temperature change | Minimal | Increases | Can feel cooler |
| Higher humidity | Same temperature | Increases | Same | Often feels warmer |
| Air leakage | Can create temperature swings | Can add/remove moisture | Creates uncontrolled airflow | Uneven comfort |
| Poor circulation | Uneven temperatures | Can vary by room | Reduced | Hot/cold spots |
Personal factors matter too. Clothing, activity level, age, and individual physiology help explain why two people can experience the same room differently.
Temperature Controls Only Part of the Equation
Given Mesa’s hot climate, it’s important to keep temperatures below dangerous levels. That’s particularly true for the elderly and other demographics more prone to heat illness. That said, your home’s dry bulb temperature is just one part of thermal comfort. Humidity, air movement, and ventilation all affect how your house feels. Even the temperature of your walls can affect whole home comfort.
Humidity Controls Evaporative Cooling
Humidity plays a major role in home comfort level in Maricopa County, particularly during the summer. The higher the indoor humidity, the warmer your house will feel, especially when temperatures are already high. While indoor humidity levels are usually low in Mesa and Chandler, they often increase to uncomfortable levels during monsoon season.
The reason this affects comfort is because humidity affects evaporative cooling. The higher the relative humidity, the slower sweat will evaporate. Once the relative humidity reaches 100% (or the air is carrying as much moisture as possible), evaporation stops. You could be sweating like Arizona Falls and it wouldn’t make a difference.
In Mesa, ideal indoor humidity falls between 30 and 50 percent. This keeps the heat from feeling suffocating while also preventing mold growth, mildew, and other air quality issues.
Air Movement Controls Convective Heat Loss
Air movement also affects comfort. While running a fan won’t lower your house’s dry bulb temperature, it can affect convective heat loss. Your skin warms the thin layer of air immediately around your body. When that air moves away, cooler air replaces it and can absorb more heat from your skin. This increases convective heat loss, which is why a fan can make you feel cooler without actually lowering the room temperature.The faster the fan, the more heat it carries away.
This is great during the summer, but it’s possible to overdo it. If the air rushing from your HVAC ventilation is going too fast, it will feel drafty. It’s important to control your system’s air velocity so it doesn’t feel uncomfortable.
Air Distribution and Ventilation Changes the Indoor Environment
Your ductwork is responsible for distributing conditioned air throughout the house. Restrictions, poor duct design, leakage, or an imbalance between supply and return airflow can make some rooms harder to heat or cool than others. These problems can contribute to weak airflow, uneven temperatures, and longer HVAC run times.
Ventilation serves a different purpose. It brings fresh outdoor air into the home and removes stale indoor air, helping manage moisture, odors, and airborne pollutants. This becomes especially important in tightly sealed homes, where uncontrolled air leakage is reduced and fresh-air exchange may need to be handled more intentionally.
The Building Envelope Is Part of Your Comfort System
To prevent heat and moisture leakage, your house needs to be properly sealed. That’s achieved with your home’s envelope. The building envelope is simply the components that create a barrier between your home’s interior and the environment outside. That includes the walls, roof, insulation, windows, doors, and foundation.
A sealed building envelope means your HVAC system can better control temperatures and humidity with minimal waste. It also affects the surface temperatures of walls, floors, and ceilings. Low radiant temperatures from the walls in the winter will actually make you feel colder. Good insulation prevents that.
Why Comfort Problems Are Usually Interaction Problems
Whether you have hot and cold spots in your house or stifling indoor humidity levels, comfort problems usually result from a combination of issues. If the different parts of your home’s comfort system interact in the wrong ways, it can negatively impact your comfort.
One common issue in Mesa homes is uneven cooling between upstairs and downstairs areas. Imagine a scenario where your system’s ductwork sends air straight over your thermostat downstairs. Meanwhile, the attic isn’t well insulated. Your upstairs areas get really hot due to the poor insulation, all while the downstairs thermostat shuts the system off prematurely.
On top of all that, the system doesn’t run long enough to control humidity during monsoon season, meaning your house is mostly hot and muggy except for a couple of rooms. With the high humidity, high heat, and sporadic airflow, your body has a hard time with both convective and evaporative heat transfer, making life miserable.
Peak Performance Home Evaluation: Measuring the Whole System
Your heating, cooling, and ventilation systems need to work together with your building’s layout and materials to keep you comfortable. Given how many factors are involved, it’s important for home comfort evaluations to consider everything as a whole. An HVAC performance evaluation isn’t complete unless it takes radiant temperature, humidity, and airflow into account.
At John’s, we conduct thorough whole home performance evaluations for this reason. We check everything from your HVAC systems to the insulation in your attic. This evaluation allows us to determine where your home is falling short. That could include anything from drafty rooms to uneven temperature control. From there, we can recommend effective solutions to make your home more comfortable and efficient.
Whole Home Comfort Takes a Comprehensive Approach
The way your body regulates temperature means comfort takes more than just changing the temperature. You need to manage airflow, ventilation, and humidity as well. These all interact in complex ways to affect the way your home feels.
Are you experiencing drafty rooms? Is it a little warm in certain areas? Do you still feel a chill when the heater is running? A comprehensive home performance evaluation can help identify problem areas. From there, our award-winning HVAC technicians can recommend energy-efficient solutions.
Frequently Asked Questions
What is thermal comfort?
Thermal comfort is the state of feeling satisfied with the conditions in your environment, including dry bulb temperature, humidity, air movement, and radiant temperature.
Why can two people feel different temperatures in the same room?
For various physiological reasons, different people often lose body heat at different rates. Their position in the room can also have an effect, especially when it comes to airflow and radiant temperature. Someone standing by the window in winter will feel colder than someone near a heating vent, for instance. The job of home comfort specialists is to try to equalize that as much as possible.
Why does 72°F feel comfortable in one house but uncomfortable in another?
Air movement and humidity can dramatically affect how comfortable any temperature feels. That’s especially true when it’s warmer (which is often in Mesa). If you have a soft breeze from a ceiling fan and low humidity, 72°F will likely feel comfortable. A home with high humidity and stagnant air, on the other hand, will feel stifling.
How does humidity affect how hot or cold a room feels?
Home temperature and humidity have a complex relationship. When the humidity levels are higher, a warm room will feel much hotter. The reason for this is it takes longer for water—including sweat—to evaporate when the air is already carrying a lot of moisture. When sweat doesn’t evaporate, it will keep heat trapped on your body for longer, making it feel hotter than it actually is.
What is dew point, and how does it affect home comfort?
The dew point is the temperature at which air can no longer hold moisture. At that point, it condenses as dew. The dew point is usually lower than the dry bulb temperature (the regular temperature as measured by a thermometer). When an object’s temperature reaches the dew point, water vapor will condense. That’s why cold soda cans will look like they’re sweating.
Dew point shouldn’t be confused with wet bulb temperature, which measures how cold air can get through water evaporation. It’s always somewhere between dry bulb temperature and the dew point. At 100% humidity, the dry bulb and wet bulb temperatures are the same, meaning no evaporation occurs.
Why does moving air make you feel cooler even when the temperature stays the same?
As your body transfers heat through convection, the surrounding air will hold that heat. If that air isn’t displaced, it will get to the point where it can’t absorb any more. Displacing it with a fan or soft breeze can make you feel cooler, which is why HVAC airflow is so important.
Can cold windows and walls make a room feel colder?
Cold surfaces can indeed make a room feel colder. Your body constantly exchanges radiant heat with the surfaces around it. When nearby windows or walls are much colder than your skin, you lose more radiant heat to those surfaces, which can make the room feel colder even when the air temperature itself is comfortable.
Can a house be too airtight?
Technically, yes. Your home’s building envelope should be sealed, but you still need good ventilation to pair with it. Without adequate ventilation, you’ll get stale air and trapped moisture. In addition, fumes from gas appliances may backdraft into your home if not properly ventilated.
Why do some rooms stay hotter or colder than others?
Uneven heating and cooling can occur for a number of reasons. Your ductwork might have too many bends or other restrictions that limit airflow. The thermostat may be measuring the bottom floor’s temperature while heat rises upstairs. Vent placements may be competing with radiant heat from windows and walls. Your HVAC equipment may even be the wrong size. Our home comfort technicians can identify the issue and resolve it for you.
How does insulation affect thermal comfort?
Insulation affects heat transfer in important ways. Essentially, if a wall isn’t well insulated, it will tend to match the outside temperature. During the summer, that means your walls get warmer. In the winter, they’ll get colder. The wall will then affect how you feel in the room through radiant heat transfer.
How do air leaks affect temperature and humidity?
Your ducts are meant to transfer conditioned air directly into each room in your home. When there’s a leak, some of that conditioned air seeps out before it reaches your vents. As a result, the system might not be as effective at managing your home’s temperature. Moisture can also seep through, affecting humidity levels.
What is sick building syndrome?
Sick building syndrome is when people feel physically unwell inside buildings with poor air quality. Common symptoms are headaches, dizziness, chronic fatigue, irritated eyes, and trouble concentrating. Improving indoor air quality may help address sick building syndrome. Call us for an air quality evaluation if you’re in Mesa.
What does a whole-home comfort evaluation measure?
We start our home comfort evaluations with an interview to understand your concerns regarding comfort and utility costs. From there, we’ll inspect your HVAC equipment and your home, including the basement, attic, and any crawl spaces. We’ll also use diagnostic tests and infrared technology to find leaks in your building envelope and ductwork. Finally, we’ll compare your utility bills to similar homes to see if there’s any energy being wasted.