Central HVAC systems have become a fixture of modern home comfort. They’re so common now that most people tend to take them for granted. However, there’s quite a bit of fascinating engineering and technology involved in keeping your Sandy, UT home warm in the winter and cool in the summer. So, if you’re one of the people who turn on your heat or air conditioning and wonder how this all works, this article’s for you! Here’s a complete explanation of how the major components of a typical central heating and cooling system work.

The Basics of Furnaces

Here in the United States, the majority of homes rely on natural gas-powered furnaces for heat in the winter. So, we’ll begin by discussing a bit about how they work. In most cases, natural gas-powered furnaces use the combustion cycle to burn the gas, which heats the air that then circulates around your home. Of course, it’s a bit more complex than that.

For one thing, most natural gas-powered furnaces rely on a network of ducts to carry air between the rooms of your home and the furnace itself. And, they also require an electrically-powered blower fan and a flue or chimney to vent byproducts of the combustion process outside your home.

The heating process begins with a signal from your home’s thermostat. That signal tells your furnace’s control board to open the system’s gas valves and trigger its ignition system. The ignition system lights the gas on fire as it flows out of a series of burners. As this happens, the byproducts of the combustion process exit your home via the flue or chimney. That’s just the first phase of the heating process, however.

While your furnace starts warming up, its blower fan will also turn on, drawing air through your home’s return air vents and into the furnace’s heat exchanger. You can think of the heat exchanger like the radiator in your car—but in reverse. As the air passes through the heat exchanger, the heat from the burning natural gas warms it to the system’s preset air temperature. That hot air then passes through your home’s ductwork, where it can reach air registers installed throughout your home.

During the heating cycle, your thermostat keeps track of the air temperature in your home. When the air reaches your desired temperature, the thermostat sends another signal to the furnace. This time, the signal closes the gas supply valves and turns off the blower motor, ending the heating cycle.

The Basics of Central Air Conditioners

In most homes with central air conditioning systems, you’ll find that they’re tightly integrated with the home’s furnace. They share the same ductwork and blower motor, as well as the home’s thermostat. However, they also have some additional equipment installed, both inside and outside the home.

The most obvious part of most central air conditioning systems is their outdoor units. To the untrained eye, they look like large box fans, and that’s not too far off from what they are. Besides the fan, however, you’ll also find a large condenser coil and a compressor in a central AC system’s outdoor unit. The purpose of the outdoor unit, in a nutshell, is to expel the heat from inside your home into the outdoor environment.

Inside your home, you’ll also find an evaporator coil installed either above the home’s furnace or within the central AC’s air handler. It’s where the system captures heat from the home’s air so it can carry it outside. How a central AC system does that, however, is the most interesting part.

Air conditioning systems rely on the refrigeration cycle to function. Your home’s air conditioner works almost exactly like your home’s refrigerator but in reverse. That process relies on two major concepts. The first is that the pressure and temperature of a refrigerant are closely related. The second is that temperature is a relative concept.

In an air conditioner, you’ll see those concepts in action. The process begins, just as with your furnace, with a signal from your thermostat. The signal tells the system’s blower fan to turn on, pulling in hot air from your home and pushing it through the system’s evaporator. At the same time, the outdoor unit will also activate by turning on its fan and compressor. The compressor begins to increase the pressure on the system’s refrigerant — typically R-22 or R-410A — which turns it into a superheated gas. That gas then circulates through the condenser coil, where it radiates its heat away with the help of the unit’s fan.

In the process, the refrigerant turns back into a supercooled high-pressure liquid state. From there, the refrigerant passes through an expansion valve, where it expands into a cold vapor. That vapor travels inside your home and through the evaporator coil. As it does, the hot air from inside your home that’s passing through the evaporator coil transfers its heat to the refrigerant, turning it back into a low-pressure, superheated gas. Then, the cycle begins again.

Just like with your furnace, the air conditioner turns off once your thermostat tells the system that it’s achieved the proper temperature. When that happens, the thermostat signals the air conditioner to turn off the components of the outdoor unit and the blower fan. The system then waits to reactivate when conditions require it.

What About Heat Pumps?

It’s also interesting to know that heat pumps, which are quite common these days, work much like air conditioners. The difference is that heat pump systems can provide a home with heating in the winter and cooling in the summer, all within the same unit. They can do this because they contain a reversing valve, which allows them to capture heat energy from the outside air in the winter. They then carry that heat inside to heat up your home.

That’s possible due to one of the concepts we identified above—that temperature is relative. In the winter, even when the mercury drops to freezing and below, there’s still heat energy available in the outdoor air. Since the refrigerant in a heat pump reaches the outdoor unit at a temperature far colder than the outside air temperature, it will still absorb that heat. With the right heat pump technology in place, that process will keep working all the way down to -15 degrees Fahrenheit.

Consult the Heating and Cooling Professionals

We at Main Street Heating & Cooling have been able to provide the finest heating and cooling installation, repair, and maintenance services to homeowners and businesses in Sandy, UT and the surrounding areas for the last decade. Plus, we’re a family-owned business that understands how important your home’s comfort is to you and your family. We take pride in helping you to maintain your home as a space that’s as welcoming and cozy as you want it to be. Therefore, the next time your home has a heating or cooling issue, make Main Street Heating & Cooling your first phone call, and we’ll do whatever it takes to make things right.

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