In a nutshell, a central HVAC system heats or cools your home by feeding heated or cooled air through your ductwork. While the process seems simple enough, getting your home to the perfect temperature requires a lot of moving parts with a lot of different components at play.
Understanding the central heating and cooling processes will help you better maintain your HVAC system. Once you know the basics, you’ll know exactly what’s going on in your home the next time you hear your HVAC device kick on.
Air conditioners function by taking heat and humidity from your home and releasing it outside, to ultimately drop the temperature in your home. In order to complete this process, all parts of the central cooling system must work together.
In most cases, central air conditioning refers to either a split-system air conditioner or a heat pump, which both have an outdoor and indoor unit. The indoor and outdoor units work together to distribute cool air through a system of ducts in your home. Together, they are composed of five main parts: a thermostat, an outdoor unit (which holds a fan, condenser, and condenser coil), an indoor unit (which holds a fan and evaporator coil), copper tubes that connect the outdoor and indoor units, and ductwork throughout the home. While a split-system AC only cools, a heat pump can reverse the flow of refrigerant to heat the home, so the process works in reverse (more on that later!).
A packaged air conditioner is the final type of central cooling. A packaged unit works the same way as a split system AC or heat pump, except the whole unit sits outside the house; there is no equipment inside the home. The packaged unit takes air from your house through the return ductwork, cools it, and then supplies it back to the house through a second set of ductworks, called the supply ductwork.
Central cooling kicks off when a thermostat senses that the temperature in your home needs to be changed. In the case of central cooling, the thermostat will alert your cooling unit that the temperature needs to drop, and all parts will work simultaneously to get your home to your desired temperature. Once the systems are alerted, they take these steps to cool your home:
Central heating systems can work in the same general way as central cooling systems by moving air around to change the temperature in your home. Instead of moving hot air out, central heating systems move hot air in to get your home to your desired temperature. But, keep in mind, this isn’t always the case. Depending on which central heating system you own, your HVAC device might actually be producing its own heat.
There are two main options for central heating systems: heat pumps and furnaces.
All central heating processes start the same way central cooling processes do: a thermostat registers the temperature and kicks off the HVAC system.
As we mentioned before, heat pumps have the same parts as a split-system air conditioner and work in the same way when they’re needed for cooling. When the temperature drops and a heat pump needs to provide heat, the process essentially reverses itself. Once a heat pump registers the function shift, a reversing valve in the outdoor unit kicks on. This allows the heat pump to absorb heat energy from the outside air and transfer it into the home to warm it up, instead of taking heat from the home and putting it outside to cool it down. The reversing valve is never something that the homeowner needs to touch; the heat pump knows to switch functions on its own!
Furnaces, on the other hand, function in a totally different way than other HVAC products. While the thermostat still kicks off the heating process, all furnaces produce heat from a gas source, like propane. Depending on the type of unit you own, the gas source could be located in an outdoor unit or underground, but both will be connected to your home via a pipe. Once your gas source is connected, the furnace follows these steps to raise the temperature:
As we’ve already mentioned, thermostats are essential components of central heating and cooling systems. Without thermostats, your HVAC system wouldn’t be able to tell when your home needed a temperature change.
Today, most homes are equipped with an electronic thermostat. These are electronic devices attached to your wall with sensors that determine if your home is at the correct temperature, then communicate that message through wires to your HVAC device. Electronic thermostats are also referred to as smart thermostats, because they can allow you to program different functions and temperatures.
Homes with older HVAC systems might have non-programmable thermostats. These systems function with either a bi-metal or metal strip. When the temperature in your home drops or rises, the strip senses the change and moves to one side, causing mercury inside the system to flow to that side. When the mercury flows to one specific side, that signals to either the heating or cooling device that it’s time to go to work.
Smart thermostats make controlling your HVAC easier and more efficient. Depending on which kind of electronic thermostat you own, they can come with scheduling features, voice activation, app integrations, and more.
Scheduling features allow you to pre-program your desired temperatures based on your routine, depending on time or day of the week. This means, you can program your home to be 72 degrees during the week while you’re at work, but 68 degrees on the weekends when you’re home. After pre-programming, the thermostat will know to send signals to your HVAC device to make your home the ideal temperature for that day.
Some smart thermostats allow for voice control, so you can change the temperature without even getting up from the couch. Others can be linked to an app, so you can raise the temperature in your home while your family is out running errands but lower it before you get back from a long, hot day at the beach.
Understanding heating and cooling product installation is important before you buy an HVAC system. HVAC systems should always be installed by a licensed HVAC professional and homeowners should never attempt any kind of installation or maintenance on their system themselves. But there are steps you can take before installation to ensure everything runs smoothly and your HVAC device is the perfect fit for your home.
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