A Look at How Furnaces Work

January 18, 2022
Furnace Services in Roseville, MI

We all depend on our furnaces to keep our homes toasty warm when Mother Nature does her worst, but the average Michigan homeowner doesn’t always fully understand the process that takes place in order to heat up the home. There are a lot of advantages to understanding the basics about how your furnace operates, because you’ll able to troubleshoot problems more effectively in the event of service issues. It can also help you make an informed decision when it inevitably becomes time to replace an older furnace that’s approaching the end of its anticipated operational lifespan.

You have many great home furnace models to choose from, and you owe it to yourself to find a team of furnace and HVAC professionals that you can trust with the installation and repairs. C & C Heating & Air Conditioning offers professional furnace and HVAC services in Detroit, Michigan, and the Macomb County area. Here’s a quick look at how your home furnace works.

The Heating Cycle

Every homeowner should be quite familiar with the sounds of a furnace or HVAC system as it cycles on and off. The way that the heating cycle works is pretty easy to understand. Each time that the thermostat senses a difference between the desired temperature and the actual temperature in your home, the thermostat initiates a call for heat that instructs your furnace or heat pump to turn on.

Older furnaces typically featured a pilot light that remained lit at all times to provide the initial fuel for the furnace’s burners to initiate the heating process. There are also furnaces with a direct ignition spark that functions similar to the spark plug in a car. Modern systems now have a hot surface ignition or heating elements that produce heat for your home.

Older furnaces allowed radiant heat to rise into the heat exchanger on its own, which was notoriously inefficient. Modern furnaces now include a motor that pushes the through to the heat exchanger for a preset amount of time. In a gas furnace, a gas valve is opened to provide fuel for the burners.

Across from the burners is a flame sensor that monitors the burners for proper functioning, and a low-voltage signal passes to the flame sensor to confirm that the burners are operating properly. When the home reaches the desired temperature, the thermostat then sends a signal to the furnace’s electronics to initiate a shutdown. The furnace will then begin cooling down so that it will be ready to restart again the next time a call for heat is initiated by the thermostat.

Safety Features

The heat sensor in the modern thermostat also serves an important safety purpose in the event of a problem. The heat exchanger is vulnerable to cracks and stress fractures because of the prolonged exposure to extreme heat, and the sensors will trigger a system shutdown in the event of a breach. This safety feature is a good early warning system for more serious problems, and it has been a welcome and much-needed upgrade.

Inside Your Unit

Here’s a quick look at the main internal workings of your furnace. Remember that with the exception of changing your air filter, you should never attempt to perform any service on your own.

1. Blower Motor

The blower distributes warm air throughout the home’s ductwork. The blower fan circulates air for your air conditioning system as well, which is why having compatible heating and cooling systems is important.

2. Exchanger

The exchanger is a series of metal tubes or coils that hold heat. Air moves across the heat exchanger and into your ductwork to heat your home.


Just like the engine in your car, the furnace has a combustion chamber that ignites fuel to generate an exothermic reaction. Keeping the combustion chamber clean and undisturbed is crucial to the system performance, and it’s one of the areas that’s cleaned during your annual maintenance visit.

4. Air Filter

Your air filter is important for both air quality and proper furnace functioning. It helps to prevent future service issues by keeping dirt and dust particles out of your furnace parts.

Differences Between One-Stage and Two-Stage Furnaces

An old one-stage furnace only has an “on” and “off” setting, which doesn’t really give homeowners a lot of options to adjust the temperature to their personal comfort level. A two-stage furnace will have one additional stage, usually around 60-70%, which can reduce energy usage, increase your comfort, and reduce wear and tear on your system. A variable-speed furnace offers the most control by offering five or more stages of operation.

The key differences in functionality between these models will be the blower motor and the thermostat. A more sophisticated furnace will require a more sophisticated thermostat, and a variable-speed furnace needs a blower motor that can modulate between stages to match the furnace’s heating output.

Annual Fuel Utilization Efficiency Rating

Annual Fuel Utilization Efficiency (AFUE) is a measure of how much heat generated by a furnace actually goes directly toward heating your home and is expressed in percentages. Standard furnaces are generally 80% efficient, and “high-efficiency” furnaces have an AFUE rating of 90% or higher. High-efficiency furnaces have an additional heat exchanger known as a secondary heat exchanger where the flue gas undergoes further heat exchange to improve AFUE and reduce heat loss.

Furnace Maintenance

Furnaces have a normal life expectancy of 15-20 years. It’s often a better idea to replace a furnace that’s approaching the end of its expected operational life rather than waiting for the unit to break down beyond repair. The most important thing that you can do as a homeowner to keep your furnace functional is to change your air filters at least every three months. It’s cheap and easy, and it’s one of the most effective ways to prolong the life of your unit.

It might be tempting to spend a few extra dollars on the more expensive air filters at the hardware store or home improvement retailer, but they’re rarely worth the money. Additionally, they might not work with your system at all. Don’t forget to also schedule annual furnace maintenance at the same time that you schedule your annual HVAC system preventive maintenance visit so that you can enjoy peace of mind all year long!

Our team at C & C Heating & Air Conditioning has been proudly serving Detroit, Michigan, and the Macomb County area since 1948, and we’re always happy to show you the latest high-efficiency furnace models from top manufacturers and ways to maximize your savings with rebates and dealer incentives. We have the most experienced HVAC technicians in the business, and we bill for all of our HVAC and heating repair and installation services according to standard labor schedules.

Contact C & C Heating & Air Conditioning today for more information and to schedule a service appointment for professional furnace service in the Detroit metro area! We provide heating, cooling, indoor air quality, and UV lights services.

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