An HVAC system is an essential part of a home. However, along with the comforts this system provides, it can also be a source of danger. This is because many appliances that are part of HVAC are combustion-powered, and one of the by-products of combustion is carbon monoxide. If carbon monoxide leaks from your combustion appliances, it is a great danger to everyone in the household.
Carbon monoxide kills hundreds of people and injures hundreds of thousands more per year, yet cannot be detected by human senses. This is why it is important to get regular checks and maintenance for your HVAC system to avoid being in a deadly situation due to carbon monoxide. In this way, HVAC professionals serve as an essential barrier between homeowners and the dangers of carbon monoxide poisoning.
HVAC stands for heating, ventilation, and air conditioning. Components of this system can include furnaces, boilers, heat pumps, air conditioners, and ductwork. Water heaters are not part of the HVAC system, but some HVAC technicians will also service water heaters. Typically, heat pumps and air conditioners will run on electricity, but a few are powered by combustion. Natural gas is commonly used in furnaces and boilers, although there are many that use electricity as well.  The needs of each type of appliance will differ, so it is important to be aware of what kind of appliances are in your home and how they are powered. Keeping up on maintenance will help prevent malfunctions that lead to carbon monoxide leaks or catch them early before they lead to injury or death of a loved one.
NCOAA recommends all fuel-fired appliance (natural gas, propane, heating oil) gets serviced once a year. This should include an inspection of the venting on these appliances to ensure that there are no issues that could lead to exhaust gases, like carbon monoxide, spreading into the home.  Annual service needs to include combustion analysis during which the HVAC professional checks that the appliance is getting the correct mix of fuel and air in the combustion process. Having an HVAC professional check appliances and fix any problems is an important safety measure in preventing carbon monoxide poisoning in the home.
When hiring an HVAC professional to inspect your home, you should ensure that they will be doing tests for carbon monoxide. Small cracks or other problems may not be visible but can be identified with leak detection equipment, which carbon monoxide measurements can achieve. You can ask potential technicians if they will be conducting these tests, or you can hire a technician with a carbon monoxide certification. There are several programs that technicians can complete that train on carbon monoxide safety and measurement. Programs with a focus on carbon monoxide safety include:
Combustion Performance and Carbon Monoxide Safety by the National Comfort Institute (NCI) 
Gas Furnaces Service Certification by North American Technician Excellence (NATE) 
Carbon Monoxide Safety Training by Carbon Monoxide Safety Association (COSA) 
Carbon Monoxide & Combustion Analysis, Carbon Monoxide Safety, and Residential Energy Auditor Curriculum by ESCO Institute [6,7]
There are a few tools to help find a technician who will do carbon monoxide checks along with their inspections. My Home Comfort shows NCI-certified HVAC technicians near you. All you have to do is type in your zip code at this link (https://www.myhomecomfort.org/find-a-contractor/) and look for Carbon Monoxide Safety & Combustion Analysis certifications. HVAC 911 shows technicians in several areas who will inspect the safety mechanisms that prevent carbon monoxide from poisoning your home… investigate the heat exchanger for cracks… [and] check the flue to ensure it’s venting properly.” 
Getting yearly maintenance on your HVAC system is a simple way to help protect your family. HVAC professionals are an important element in the fight against carbon monoxide poisoning. You can learn about further measures you can take against carbon monoxide poisoning at https://www.ncoaa.us/preventive-measures.