What Is HVAC? Basics of Heating and Cooling

What is HVAC? It’s Heating, Ventilation, and Air Conditioning. If you only wanted to know what the acronym stands for, there you go.

But what is HVAC really? Not sure what I mean by that question? I’ll explain.

Heating and cooling is a lot more complicated than many people realize. It involves metalwork, electrical work, plumbing, combustible and flammable materials, and precise calculations that require specialized tools and training.

For that reason, it can be intimidating. And that stinks when you have to spend thousands on a new HVAC system or repair.

Fortunately, the basics can be learned and absorbed by anyone. And that’s what we’re here for. At Fire & Ice, much of what we do is educating our customers so that they’re no longer intimidated

So what is HVAC? Let’s find out together.

What’s in an HVAC System?

When we talk about HVAC, our thoughts go to air conditioners and furnaces. Maybe heat pumps if you have an electric fuel system instead of a gas furnace.

But there’s a lot more than that. The list below isn’t comprehensive, but it will give you an idea of just what we mean when we say that your HVAC is truly a “system” that works harmoniously together:

• Air Conditioner, which cools the home.
• Heat Pump, which heats and cools the home depending on the time of year.
• Furnace, which heats the home.
• Air Handler, which manages your airflow.
• Blower Motor, which responds to the needs of the system to increase or decrease airflow. Some blower motors have only one setting, while others are multi-speed.
• Filter, which keeps your air clean and ideally allows for free airflow that doesn’t hinder system performance.
• Ventilation flues and pipes, which vary in nature depending on what type of system you have.
• Electrical work, which provides power to different pieces of equipment.
• Gas line, for those homes with gas furnaces.
• Ductwork, which carries air both from the central blower fan and also carries air back to it from the home, to filter and recycle it.
• Thermostat, which regulates the entire system and allows you to control it.
• Dehumidifiers and Humidifiers, which operate seasonally to maintain proper moisture levels in your home.
• Air Purifiers like UV lights that kill bacteria and other harmful particulates in your air supply.
• Ductless Mini-split units, which can both heat and cool and are generally used for individual rooms or zones of your home.

Sound like a lot? It is. That’s why HVAC technicians are often skilled carpenters, metalworkers and electricians in addition to being trained specifically in HVAC equipment.

These definitions can expand even further if we include lesser-used technologies like wood and corn furnaces, or geothermal heat pumps that utilize the ambient temperature of the Earth to regulate your home’s temperature. We’re going to focus on the most-used technologies, but the larger world of HVAC includes many older and cutting-edge technologies that are utilized in different settings.

Heating

First, let’s mention the smaller stuff. Space heaters, fireplaces and other smaller sources of heat are included in a home’s heating. These are not full, whole-house solutions, though, so we’ll be talking about these larger systems.

The home heating cycle is a multi-step process that incorporates much of the equipment listed above.

The thermostat will sense the temperature in the home (sometimes using multiple sensors throughout the home), and call for heat.

Depending on your fuel source, the next step can vary. For gas furnaces, older systems often have an ever-burning pilot light. The gas line will open to allow a certain amount of fuel, and the pilot light will ignite the furnace’s burners. In newer systems, there is an igniter plate that accomplishes the same task, but without the constantly burning pilot light.

In electric furnaces, heating coils (think of a very powerful toaster...the technology actually works similarly) will begin to heat up.

The furnace’s blower motor will turn on to begin moving the heated air throughout the home. This also begins the process of air returning to the unit through return air ducts. Depending on the type of furnace you have, the blower motor and burners may have different stages to produce different levels of heat. For example, the furnace might run at 70% capacity when only a little bit of heating is needed. This saves energy and money.

Before entering your home proper, in a gas system the gas travels through a heat exchanger. This is a series of metal tubes that hold heat from the furnace’s heat source. The air of your home is warmed when air is moved across the heat exchanger and into your ductwork. Excess gas is then vented outside the home.

RELATED: The Complete Guide to Home Furnaces

Ventilation

When you think about ventilation, you might think about the exhaust flue that sticks up out of the roof of many homes. This is part of ventilation in heating and cooling, but isn’t the entirety of it.

One of the chief purposes of HVAC is to manage humidity levels. As we’ll talk about in the air conditioning section below, venting humidity from the home is one of the primary jobs of your air conditioner or heat pump.

So when air is moved from inside to outside, or vice versa, this ventilation takes place and it’s with the intent of regulating both the internal temperature and humidity, which are closely tied to one another.

During the heating process in gas furnaces, a small percentage of waste gas will be produced. If you have a traditional furnace, this waste will be vented out of a chimney flue.

In many modern systems, a larger percentage of gas is used to heat your home, which makes the furnace more efficient. However, this means that the remaining waste gas isn’t warm enough to simply rise from the home, and can create puddles of moisture around your unit. To combat this, PVC pipe that exits the side of the home is often used to ventilate these systems.

Natural ventilation is also included in this category, and can include things like home and window construction to allow excess heat to escape the home naturally. Most modern American homes don’t have many of these considerations, but you often see natural ventilation play a role in the construction of larger office buildings, churches, and other prominent structures.

Air Conditioning

The cooling cycle for a home is similarly complex, and it works differently than many people realize.

To start, let’s talk about your refrigerant. You might hear it referred to as Freon, though this is technically a branded term, like calling a tissue a Kleenex.

In any case, refrigerant is the stuff that exists inside your cooling system, and it changes state from liquid to gas depending on its temperature. As it changes state, it’s also traveling back and forth from your inside unit to the outside unit.

At certain temperatures, the refrigerant absorbs heat and humidity. At others, it expels the heat it absorbed. So the cooling process is designed to change the state of the refrigerant at the right time to absorb and expel heat and humidity.

If you have a heat pump, it’s the same process, but it can be reversed. So rather than only expelling heat and humidity from your home, it’s actually pulling it into your home from the atmosphere during the colder months.

So when you think about air conditioning, don’t just think about the outdoor unit! It starts with the condensing coil (sometimes just called a condenser) inside your home, which absorbs the heat and transfers it into your system. The evaporator coil in the outdoor unit then expels it into the atmosphere. During all of this, an expansion valve (sometimes called a metering device) regulates the amount of refrigerant that’s needed, so that you maintain the correct temperature in your home.

Sound complex? It both is and isn’t. The basic process is quite simple, but the precise calculations to maintain the correct pressures for the refrigerant and proper transfer of heat can be quite complicated. It requires specialized equipment to ensure your system is tuned properly.

Filtration and Air Purification

Your air filter is quietly one of the most important pieces in your HVAC system. Air filters

Some do, at least. Not all filters are created the same, and there are various ways to measure their efficiency.

MERV stands for Minimum Efficiency Reporting Values. This rating measures a filter's ability to capture particles between 0.3 and 10 microns in size. This can be important for many airborne viruses and other contaminants.

CADR stands for Clean Air Delivery Rate. It measures the amount of air (in cubic feet per minute) that has had all particles of a particular size removed from it before it’s distributed throughout your home. Higher numbers are better.

Some filters will have a higher CADR rating to capture a particular kind of particle vs. another. Dust, smoke and pollen require different CADR ratings for a filter, because the particles are different sizes.

If a filter is clogged, it will make your entire system work harder due to the reduction in airflow. That’s why it’s important to change or clean your filter regularly.

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Humidity Control in Homes

As we discussed earlier, humidity control is a huge part of an HVAC system’s job. Without humidity control, temperature control is impossible.

Problems Associated With Humidity

1. Dry, itchy skin in the cold months
2. Persistent cough when air is dry
3. Cracked floorboards due to dryness
4. Mold growth in high humidity
5. Increase in dust mites in high humidity, which leads to bug infestations
6. Increased chance of contracting the flu or other viruses in low humidity
7. Spreading of allergens in the spring and summer

Equipment That Controls Humidity

Air Conditioner/Heat Pump - As discussed earlier in the air conditioning section, a lot of what an AC or heat pump does is remove humidity from the home.

Whole-Home Humidifier - This can help keep moisture in the air in the winter by injecting moisture into the ductwork to travel throughout your home.

Whole-House Dehumidifier - This can be ducted to your system or operate freestanding in the basement. Regardless, it affects the entire home and can make your home cooler and reduce the time you need to run your air conditioner.

RELATED: Indoor Air Quality: HVAC Humidity Problems & Solutions

HVAC Efficiency and Operation

Efficiency is measured in one of a handful of different ways, depending on the equipment being measured.

SEER Rating (Seasonal Energy Efficiency Ratio) applies to air conditioners and the cooling side of heat pumps. It measures the ratio of the cooling output of an air conditioner over a typical cooling season, divided by the energy it uses in Watt-Hours. In short, it’s how efficient your unit cools.

AFUE Rating (Annual Fuel Utilization Efficiency) is for furnaces, and is measured in percentages. It calculates how much of your fuel source (gas or electric) goes toward heating the home. The remainder is vented. A standard furnace is 80% efficient, while top-of-the-line gas models can reach 98% efficiency. Electric furnaces are 100% efficient, but the cost of electricity can make them an expensive option in some areas despite this.

HSPF Rating (Heating Seasonal Performance Factor) applies to the heating side of heat pumps, and as with the others, higher ratings translate to increased efficiency.

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RELATED: SEER, AFUE and HSPF Ratings in HVAC: Why They Matter

The HVAC Industry

Manufacturers produce HVAC equipment, often utilizing global supply chains and materials from various countries. Production of the equipment may happen all at the same facility, or it may be split between facilities. Several manufacturers have large production and distribution facilities here in the United States.

Some contractors may allow you to purchase equipment and have them install it, but verifying quality and ensuring low prices can be tricky with that method. Contractors (like us here at Fire & Ice) generally partner with one or more manufacturers to facilitate bulk orders for customers that leverage economies of scale.

Some companies will contract out their work to independent contractors, while others retain full-time employees that only work for their company.

Fire & Ice has an on-site training facility since HVAC technology is always evolving. Ongoing training is important to the industry, but isn’t a given at each company. That’s also why we have full-time, W2’d technicians, so that we can make our products and services better year after year, rather than working with rotating contracted help.

Some companies specialize in a particular type of product. Aprilaire, for example, focuses on indoor air quality products like filters, air purifiers and humidity-controlling products.

How To Learn More About HVAC

Want to learn more? You’re in the right place! Fire & Ice has one of the most comprehensive Learning Centers for residential HVAC anywhere on the internet.

I’ve included a handful of useful links below to get you started, and feel free to explore the hundreds of articles and videos in our resource center to answer any questions you might have about your next heating and cooling project.

NEXT STEPS:

• Your Top HVAC Questions Answered
• Air Conditioner, Heat Pump, Furnace & Air Handler: What’s the Difference?
• Common HVAC Myths Busted