Imagine it's 90 plus degrees outside with a nice dose of humidity in the air.

You've been working outside all day weeding your prize vegetable garden, which is no small feat.

You're hot and sticky. You've sweat pretty much everywhere.

The one thing you crave is hitting that wall of cold air the minute you walk into your house and relaxing in it with a tall glass of ice water.

You open the door.

You hit the wall of air, but it sure isn't cold. It's as hot and humid as the air outside.

What the heck?

You have just experienced a failure of your HVAC system.

Do you check things out and handle it yourself or should you call a professional?

The answer to that question and many more you have about your HVAC system are just a scroll away.

Keep reading to discover everything you ever wanted to know about HVAC systems and how to maintain them.

HVAC stands for heating, ventilation, and air conditioning. Essentially, your home's HVAC is its temperature control system.

It's what keeps your home cool in hot weather and warm in cold weather.

It is the saving grace on days when temperatures go super high or super low and keeps you from sweating it out or ending up with icicles for fingers.

The fact is:

We use our HVAC system practically every day. And until they break down, we barely think about them.

That needs to change.

You should appreciate the modern HVAC system because, in the past, things weren't always so comfortable.

The idea of heat has been around since fire was discovered. Early people probably built fires in their caves to combat the cold in winter. They huddled around it to protect themselves because they likely had experienced what happens when the human body gets too cold.

On the flip side:

Someone once probably waved their hand in the air and discovered it provided a cool bit of air

Ancient times

Ancient people in Greece and Rome also appreciated warmth. They actually created fire channels that ran under marble flooring to provide radiant heat. These were like the low-tech version of today's radiant flooring.

And that's not all:

The Romans also had the hypocaust, which was similar to the central heating units of today that use radiant heat. They were on top of staying warm and toasty.

Fun Fact: The Romans were the first to use a warm air heating system.

The Egyptians didn't forget about cooling, though. They are famous for their man-powered fans.

These early attempts were okay, but better things were on the horizon.

1400s

Leonardo Da Vince continued with the idea of using a fan for cooling, but he didn't need to enslave people to make his fan work. It ran on water power.

This century didn't really expand on heating. The focus was more on ventilation at this point.

People had long been cooking with wood stoves and were getting pretty darn tired of smoke-filled homes.

With the advent of the chimney, it meant the smoke could flow outside.

Blessed ventilation.

Fans were also used to help remove toxic gas in mines, helping to make mining safer for workers.

Chimneys came to America in the 1500s, and mines in France really began using fan technology, expanding on the previous decades' inventions.

This century also brought the introduction of the gravity exhaust ventilation system.

Plus, Galileo invented the thermometer.

Finally, people had a way to tell just how hot or cold it was, but his thermometer wasn't really accessible to everyone.

You've probably seen the modern version of a Galileo thermometer.

Back in his day, though, it wasn't as easy for the average person to read.

For that, people had to wait until the 1700s.

1700s

We'll skip the 1600s because there isn't much that happened on the HVAC front, but in the 1700s inventors really got back into the swing of things.

Daniel Gabriel Fahrenheit introduced the mercury thermometer in 1714.

Now, when Aunt Tilly complained about being chilled, you could check the thermometer, see it was 70 degrees, and tell the lady to put on a sweater because you weren't about to fire up the wood burner.

The first centrifugal fan ventilator came out of this decade, too.

But wait, there's more:

Benjamin Franklin invented the first steam heating system, and direct fired heat exchangers were first used in England.

The 1700s also brought us the boiler system and hot water heating systems.

Yay! No more heating pots on the stove and lugging them to the bathtub!

1800s

By the 1800s, things were heating up.

In 1861, William Siemens invented the electric furnace that had heated coils and fans.

The first blast furnace came in 1885 from inventor Fayette Brown.

1900s

You could say the 1900s were a real boom for HVAC. So much happened that the whole concept of HVAC was forever changed.

Here's what happened:

In 1902, Willis Carrier created air conditioning using coils, refrigerant, and a fan. However, it wasn't until 1906 when Stuart Cramer coined the term air conditioning.

So, before then, I guess people called it the cool air thingy?

Fun Fact: Because air conditioning hadn't been invented yet, schools started giving children a break over the summer because the schoolhouses were too hot.

By the 1920s, people had air conditioning in their homes, but it still wasn't feasible for many people due to cost. So, it became huge for movie theaters to install air conditioning systems and use the cool air to entice patrons inside.

Fun Fact: AC in movie theaters lead to the creation of Summer Blockbusters because so many people went to the movies in the heat of summer.

AC was first put in vehicles in 1939, but it was such a huge hassle people really didn't want to deal with it. You had to get out of the car to turn it on and off.

No thanks. I'll just let the wind cool me off.

In the 1930s, J.Q. Sherman and H.H. Schultz invent window air conditioners to really help spread this invention to the masses.

The 1900s also was when the heat pump became a thing. It was a more economical way to heat and cool a home.

In 1998, due to environmental regulations, there was a need for a new type of refrigerant. So, the Carrier Corp introduced Puron refrigerant.

By the end of the decade, solar-powered HVAC units were introduced to help save energy and make use of this renewable energy source.

2000s

Renewable energy is still a popular idea. Geothermal energy systems are being introduced.

One of the most popular...

Zoned systems. These let you control the temperature in each area of your home instead of having one control for the whole house.

Talk about ideal comfort level.

Plus, many systems are Wi-Fi enabled, and you can control them remotely through your smartphone.

It really is the future.

HVAC sure has come a long way since people used open fire to stay warm and hand-held fans to stay cool.

The whole point of an HVAC system is that it works properly to provide you with a temperature-controlled environment. An effective HVAC system will keep your home cool in warm weather and warm in cool weather with proper ventilation for excellent indoor air quality, no humidity, and no dryness issues.

This is a tall order.

To ensure effectiveness, your system needs the right components and set up to suit your home and needs.

Fun Fact: You can save up to 40 percent on energy costs by using a variable speed heat pump.

An air conditioner uses a condenser and evaporator system to cool and remove moisture from the air that it delivers to your home. Depending on the type of air conditioner, it may use the same vents as your furnace or blow out directly from the unit using a fan.

Fun Fact: A home feels cooler with lower humidity levels. This is another way air conditioning makes your home comfortable.

Every system will also include proper ventilation. This removes air from your home, remove byproducts of the heating and cooling process, or filters the air coming into your home.

The good news is:

Ventilation is usually built into the heating or cooling source.

But the control panel depends on your system set up. Often it's mounted on the wall or the unit and allows you to set the desired heating or cooling level based on what temperature you want your home to be.

Your system will surely include various other components, but may not include all of these components. For example, some systems don't include an air conditioner. And some may have a fan built in that you can operate independently of the furnace. Or you may not have a central unit that delivers heat but instead use electric heaters in each room of your home.

There are many ways to design an HVAC system using various components.

Just as all HVAC systems have the same general components, they also work in much the same way. The general concepts of heating, cooling, and ventilation do not really change.

Here's an idea of how each element in an HVAC system works.

Controls: A control panel that allows for temperature setting for heating and cooling. May also provide fan control.

Heating: Heating options are usually a furnace or boiler.

A furnace uses vents that run throughout the home and blows air from the furnace into the vents with a blower fan.

A boiler uses pipes that send heat to radiator units in each room of the home.

Air Conditioning: Air conditioning removes heat and humidity from a home and introduces dry, cool air.

Ventilation: Ventilation is built into the heating and cooling units to remove hot or cold air and to remove byproducts of the heating and cooling process, such as carbon monoxide and smoke. It also includes things such as kitchen and bathroom exhaust fans and ceiling fans. Some systems may also remove allergens, dust, and dander.

You can get the best possible HVAC system installed in your home, but it still won't last forever.

I know -- bummer.

Just as with a vehicle, you have to do HVAC maintenance on your HVAC system regularly to keep it running right.

Fun Fact: Energy efficiency is a huge deal. Due to standards from the U.S. Department of Energy, from 1993 to 2003, people saved $29 billion on heating and cooling.

You should get your HVAC system maintenance done twice a year. You want to do it before each major season, which is summer and fall.

In addition to those two routine checkups for your system, you should also change the filter monthly or every three months, depending on your use.

Here is a checklist of the tasks that should be done during the bi-annual maintenance.

You should be aware there is not an industry standard for what is included in bi-annual maintenance. So, make sure to check your agreement with your technician to see what he or she is doing on each visit.

Typically, a technician will do some basic tasks each season.

For the AC in the spring:

The technician will probably tighten electric connections, inspect controls, clean coils, lubricate as needed, replace worn parts and the filter, check the fans, check pressures, and verify the operating temperature.

For the furnace in the fall:

The technician will likely tighten electrical connections, inspect for leaks, clean the blower, clean the burners, inspect the ignition switch, clean the flue, replace any worn parts, and inspect the controls.

You want to do regular maintenance to keep your furnace running properly and to avoid safety issues.

Maintenance also helps to prevent costly repairs, lowers energy bills, and helps your system last longer before you need to replace it.

Fun Fact: Proper maintenance can help prevent up to 35 percent loss of heat.

Here's a deeper look at the benefits of regular maintenance.

When it comes to maintenance for your HVAC system, you may wonder if you can do it yourself or if you should hire a professional to do it for you.

If you have training and skills in HVAC, you may be able to do it yourself.

But how many of us do?

Not too many.

Your best bet is usually to call in a pro.

However, there are some tasks that you can DIY.

Just make sure you understand the difference between those things you can do and when you need a professional.

Listen up:

Working with gas and electricity is dangerous. If you try to do something that you do not have the skills to do, it could be a deadly mistake.

In this case, it really is better safe than sorry.

One of the things you can do yourself when it comes to maintaining your HVAC system is taking care of the filter.

Not only should you change it regularly so you aren't running a system with a dirty filter but also you should consider using high-efficiency filters.

Here's why:

The filter keeps dust out of the system. It ensures the system runs more efficiently and prevents breakdowns due to dust buildup.

You can also keep the area around your unit clean. Dust, debris, and dander are no good when they pile up around an open flame. All it takes is one wayward spark to send your home up in flames.

Also, pay attention to operating sounds. You can often tell if something isn't quite right by just listening to the unit when it's running.

It's also fine to check things out visually. Look for damage or wear.

Not only that:

Stay alert for odd smells, too. Gas leaks are nothing to play around with.

Now, DIY can be great for many things:

But it can also be bad for other things, namely maintenance on your HVAC system.

Professionals go through quite a bit of training to learn how to work on these systems.

They learn about safety. Not only how they can stay safe while working but also how to ensure a system is safe to use.

Making a mistake by trying to do repair work yourself can cost you big time.

If you don't happen to get injured, you could break something and end up having to replace the whole system.

And that's pricey.

Plus, most warranties are only valid if a professional technician works on the unit.

If all that is not enough, you could also get yourself into some legal trouble.

It's true!

There are laws about handling refrigerant and working with other parts of the system. If you don't know the law or have the proper training or licensing, you could end up in jail for your DIY escapade.

So, are you good and scared about trying to tackle HVAC maintenance on your own?

That wasn't the point, but at least you understand trying to do it yourself is a risky move.

You should call in a professional to do the bi-annual maintenance of your system at a minimum, but you may also call a pro to do any repair work, as well.

Here's what to leave to the pros:

When choosing someone to work on your HVAC system, make sure they are licensed to do so in your state if required.

Icon via Flaticon

Also, check their experience. They should have years working on systems either as an apprentice in training or on their own.

Make sure they are insured as well.

You can also look for someone with certification from a professional organization, such as North American Technician Excellence.

And it never hurts to get referrals and references, too.

Don't hire just any old Joe off the streets, people!

Whenever something is giving you a fit, you usually stop and think if it is worth repairing or if you should just buy a new one.

When it comes to the HVAC system, buying a new one is a huge investment, so you need to think about this for a bit.

Think about this:

There are some common signs it might be time to replace your system instead of doing another repair. These include:

Obviously, if you have a newer system, you will always go with repairing it over replacing it.

There is an exception:

If you're moving, ignore everything above and do a repair instead of replacing it.

It usually is not worth it to replace the system as it won't help with the sale of your home or get you more money on your asking price.

As long as it is safe, fix it and move on.

We've covered a lot about HVAC systems.

You probably know more now than you ever dreamed possible.

But wait!

We aren't quite finished.

Here is a look at some do's and don’ts when it comes to using and maintenance on your HVAC system.

Keep these things in mind to ensure safety and efficiency.

Okay. Now we are finished.

Hopefully, you learned a lot about HVAC.

It can be a confusing topic, but you know the basics now.

Whether it is cold or hot, the chances are good that you just want a system that runs as it should.

Nobody wants to hit the heat wall on a hot day or freeze their buns off on a cold day.

Having a properly working HVAC system is all about maintenance.

You need to find a professional and do your DIY tasks to keep your system in great shape.

If you do that, you'll have many days of temperature-controlled bliss in your future.

Have you ever had to replace your HVAC? Did you learn anything new today? Let us know your story in the comments!