How Do HVAC Systems Work? Heating and Cooling Explained

Your air conditioner cools and your furnace heats. Is that it? Are we done here?

Don’t worry, we’re just being cheeky with those questions. If you’re here, you’re interested in learning a bit more about HVAC systems, which can be surprisingly confusing.

There’s a lot to learn! Even this article, which tries to take a thorough look at the different areas of heating and cooling, is surface-level compared to the technical analysis of complex machinery and thermodynamic systems that HVAC technicians need to know to perform their job well.

So our assumption is that you’re a homeowner who needs more information to help you make better decisions for your home, and understand some basics about this expensive and important system.

Good news: we do this all the time for our customers, and we’re happy to help you as well. Let’s get into it!

Heating Your Home

First off, we’re discussing whole-home heating. Space heaters, fireplaces, and similar heaters can be useful, but they aren’t our focus.

Most homes have central heating and air that runs through a ductwork system and through vents in rooms to deliver the heated air. If this describes you (we cover less common types below), you have either a furnace or a heat pump as your main heating device.

Furnaces generally use natural gas or alternative fuel source, and ignite a burner in the main unit. This burner is connected to a heat exchanger. The heat exchanger separates heat from potentially harmful gasses, the latter of which is vented harmlessly outside of your home (either through a vent in your roof or side of the house).

ALSO READ: Furnace Heat Exchangers: Overview and Guide

The separated heat is then circulated into the ductwork, throughout the home, and into each room with an air vent.

Throughout your home you’ll also have return air vents. This allows air to circulate back down into the system to be heated, creating a cyclical pattern to airflow in the home. Before returning to be heated, the air passes through your filter. This removes particulates from the air before it’s recirculated.

For heat pump (electrical) systems, it’s a bit different. Heat pumps use refrigerant to collect heat from outside the home and transfer it inside. This can occur even in relatively cold temperatures.

Most heat pump systems have a supplemental heating source, though. Inside the air handler, electric heating strips will warm up - kind of like a toaster oven! - to provide additional heat when it’s coldest.

These heated coils are not technically a furnace, but oftentimes homeowners will refer to it as a furnace. This is technically incorrect, but since they produce similar results, it’s usually fine to refer to it however you want.

While less common, you may also have whole-home heated systems that use baseboard heaters, and your furnace may use a different fuel source such as oil, wood, or corn.

Ductless units (aka ductless mini-splits) can also be used to heat individual areas. Multiple installed ductless units can heat a whole home, but it’s somewhat rare to see this.

Cooling Your Home

If you have a central air cooling system for your home, you have an air conditioner or heat pump.

Rare instances of alternative whole-home cooling methods exist, but this is your typical home. The only exception comes with smaller homes that can sometimes be adequately cooled with 1-2 powerful ductless units. These will not be our focus, though.

Air conditioners and heat pumps basically work identically. The only major difference is that heat pumps can go in reverse as well, to heat the home. ACs are only for cooling.

Refrigerant is stored in the system and travels between the inside and outside units. A compressor and evaporator on either end cause the refrigerant to change states of matter, from liquid to gas and back again. Depending on the state it’s in, it either absorbs ambient heat or expels it. And so inside the home, it absorbs heat, then it travels outside and is expelled into the air.

It does this over and over until the desired temperature (set by the thermostat) is reached in the home.

In this way, cooling a home is more about removing heat than about adding cool air.

A big part of this process is also related to moisture removal. Humidity equals temperature to the human buddy, and so an AC is sucking moisture from the (usually humid summer) air as well.

This is why a dehumidifier can help to cool your home, as we’ll discuss in more detail below.

This ignores a lot of sub-steps and pieces of equipment that contribute to cooling a home. But now you understand the broad strokes of how your equipment regulates the temperature in your home year-round.

Ventilation in Your Home

The “V” in HVAC is often the one that goes ignored, but it’s crucial to your home’s health and comfort.

Ventilation can refer to a lot of different processes, but it’s useful to think of it in terms of airflow. If you open windows in your home to create a nice cross-breeze, you’re ventilating your home. Some of the same principles apply to HVAC systems, and their effects can be the same as well.

In a mechanical sense, ventilation relates to the venting of air from your outdoor air conditioning or heat pump unit, as well as the ventilation gases from furnaces.

But the veins of this system, so to speak, are your ducts. The ductwork carries air around, but also helps to circulate it, much like two open windows can do. Your AC or heater outputting air will struggle to do its job if the airflow from your home back into the system isn’t properly balanced.

This, then, relates to services like ductwork modification when areas don’t have proper return ducts to create an equilibrium with air circulation.

It can also necessitate ductwork cleaning, sealing, or filter replacement. The results of improper airflow due to blockages or leaks can be larger than many realize, up to and including your system breaking down prematurely.

Managing ventilation is just as important as managing your heating and cooling. Ignoring it can end up costing you thousands over time. 

Air Quality Processes and Products

While ventilation certainly touches upon air quality, there’s a whole wing of HVAC products and services that

Not everyone needs air quality products and service. Don’t let someone sell you something that you feel is unnecessary.

However, for those who do need such services, they can be immensely helpful to enjoying your home environment.

Indoor air quality is sometimes even more noticeable than inefficient heating or cooling. Sure, you might be paying more to heat your home, but it’s still warm. With air quality, though, you’ll notice the signs and feel the difference.

Some considerations for whether or not you may benefit from indoor air quality (IAQ) services:

1. You own one or more shedding pets
2. You have severe allergies
3. The home has one or more regular smokers
4. You live in an urban area with sporadic air pollution warnings
5. You notice excessive amounts of dust or debris in the air and on surfaces

How does HVAC help? Several ways:

1. Ductwork cleaning can remove tons of debris that gets continually circulated through your home.
2. A filter upgrade can trap more particles and even viruses and bacteria!
3. Ventilation adjustments can circulate air better and prevent stagnant pockets in your home.
4. Air cleaners (sometimes called air purifiers or air scrubbers) can supplement the efforts of your regular equipment to remove even more harmful material.
5. A UV light is a specific type of air purifier that can kill harmful bacteria and viruses, among other pollutants.

Air quality also relates to humidity, which is the next large area that HVAC covers.

Humidity Control

Humidity equals comfort. Don’t believe me? Go for a walk in a desert sometime, then in a rainforest, then in a carefully controlled home environment.

You don’t actually have to do that to know the difference.

Ideal humidity levels (around 50% relative humidity in the home) can prevent all sorts of problems:

• Dry cough (low humidity)
• Creaky floorboards (low)
• Lingering flu season (low)
• Dry, cracked skin (low)
• Seasonal allergies (high)
• Mold and mildew (high)
• Bug infestations (high)

Whole-home humidifiers and dehumidifiers are designed to prevent these things. Many can even be attached to your ductwork so that they’re treating the air as it flows throughout your home.

Effective humidity control is the biggest item homeowners overlook when it comes to maintaining their HVAC system, and is worth considering when you next upgrade your home.

Controlling Your HVAC: Thermostats and Smart Home Technology

Then there’s the thermostat, the brain of the whole operation.

The most sophisticated thermostats do a lot now. They can control your temperature, your humidity, make you coffee, operate on a pre-set schedule, and be controlled remotely through apps.

One of those was a lie. You can probably guess which one. The others are entirely normal, though.

Everything we talked about earlier, from air quality and humidity products to the major equipment itself, can flow through your thermostat, and smart home tech is becoming the standard for many upgrades.

This means smarter control over your home environment, ideally saving you time and money.

Putting It All Together

HVAC is everything we talked about above, but more than anything it’s all of these things working together.

None of it operates on its own, and there are tons of mechanical parts of your HVAC system that are used for both heating and cooling, which means they aren’t separate mechanical processes. Thinking about your HVAC system as a whole is important to get the most out of it.

This is why CABS Heating and Air Conditioning offers home air quality audits (free), quotes on all major and minor equipment installations (also free), and maintains one of the best reputations in the entire state for home comfort services. We don’t treat equipment as an individual sale, but as part of your home that works with everything else in your home to provide comfort, quality and cost savings.

Ready to hear more? Give us a call today!