What Does a Furnace Do and How Does It Work With Air Conditioning?
At home, a comfortable temperature is essential
Highlights
Your furnace and air conditioning unit are both parts of your HVAC system.
When temperatures rise, turn off your furnace and switch on your AC.
Your AC needs to use the furnace’s fan to circulate air.
Your furnace and your air conditioning system are two central components of your HVAC system, connected and controlled for greater efficiency. During warmer weather, you’ll need to turn off your furnace and use your air conditioner instead.
Your central air conditioning system is independent of your furnace. The outdoor unit isn’t connected to the furnace at all—but they both utilize the same distribution system (vents, fans, filters, and ducts) to push cool and warm air into your home.
Still confused about how a furnace works with AC? Keep reading.
Your Home’s HVAC System
Your furnace and your air conditioning system are part of your home’s HVAC system. They both use air ducts throughout your home to transport cool or hot air, helping your home to maintain a comfortable temperature. You can think of your heating and cooling systems as the lungs of your home, while the ductwork is the airway.
But your central AC system works independently of your furnace. In fact, the outdoor AC unit isn’t connected to the furnace at all, even though both systems use your home’s ductwork and vents to circulate cool air.
How Does a Furnace Work?
A furnace works by heating up air and sending it through the ducts of your home using a fan. During cooler winter months, your furnace helps to ensure that you stay toasty and warm inside your house.
Different types of furnaces use different fuel sources including natural gas, electricity, and propane. The blower located in the base of the furnace is used to blow both hot air from the furnace and cool air from the AC throughout the ducts to reach the vents in the home.
This begs the question: Does the furnace control the AC? The answer is no, but the systems work together with the AC using the same blower as the furnace.
How Does Your AC Work?
If you have central air, your air conditioning system works in much the same way as your furnace. But instead of taking in air from the outside and heating it, your air conditioner cools the air down. The cool air is then distributed throughout your home via ducts.
Do You Need to Run Your Furnace and Your AC at the Same Time?
So, how does the furnace work with AC? In general, you shouldn’t have both systems running at once. Not only does this defeat the purpose of heating or cooling your home, but it also means that your HVAC system will experience additional wear and tear.
In most cases, the thermostat will have separate settings for heating and cooling. Once temperatures get warm enough that you no longer need to heat your home, you should switch over to air conditioning until the cooler months return.
During the summer, you should lower (or turn off) any humidifiers attached to your furnace, since one job of your AC unit is to dehumidify air. During the winter, you want the humidifier to leave some moisture in the air to help increase overall comfort and make your home feel warmer.
The Comfort Systems Rely on Each Other for Best Performance
Your air conditioner and your furnace are two important and interconnected parts of your HVAC system. Because both the heating and cooling systems of your home are encompassed by the HVAC system, it’s especially important that you keep it well-maintained so you don’t need to shell out the cost of a new furnace. Damage to one part often leads to damage within the other. For example:
Ductwork: Damage to your ductwork leads to hot or cold air loss in your basement.
Improper air conditioner installations: AC units that aren't properly installed can bleed cool air into your furnace during the winter, making its job far more difficult.
Furnace fans: If your furnace fan stops operating during the summer, all of the cold air being produced by your AC unit won't go anywhere.
Broken thermostat: This part must be set right to engage “hot” and “cool” options appropriately.
You can protect your furnace, AC, and HVAC system by conducting regular checkups and fixing any issues that may arise right away. A good rule of thumb is to have your furnace inspected about once a year before cool weather hits in late summer or early fall.
You should also bleed your furnace yearly to ensure it runs efficiently. Doing these things can help you to catch any problems and make sure that your furnace is in tip-top shape before winter arrives. Replace your furnace and air conditioner filters regularly. If you need a new furnace, contact a local furnace installer to discuss your options.
Frequently Asked Questions
A furnace can be gas or electric. It can also be fueled by propane, oil, or wood. Electric furnaces are more affordable to install, but they may be more expensive to operate over the course of their life. Natural gas furnaces are more common and while they may cost more to install, they can cost less to operate than other options.
There are two main reasons your furnace and AC are turning on at the same time. The first could be that you’re confusing the furnace with the blower. The blower is located in the furnace and will turn on to distribute cool air from the air conditioner through the ductwork in the home. This is normal. If the actual furnace is turning on at the same time as the AC and hot and cool air are coming into the home, it could be a result of incorrect writing to a new thermostat or new systems.
Yes, the furnace and AC use the same blower. The blower is located in the base of the furnace and pushes hot air out of the furnace and into the ducts. It also pushes cool air through the home when the air conditioning is on. Even though the furnace and air conditioning work independently of one another, the blower is an essential component for both systems.
Yes. Furnaces only provide heat. Unlike heat pumps, which can both heat and cool your home in one system, a furnace is only for cozying up your house in the colder months. If you need a cooling system, as well, you’ll have to install an air conditioner separately or install a heat pump.
No. Your furnace does not run your air conditioner. Both units use the same system of ductwork to move conditioned air throughout your home, but you can have a furnace without having an air conditioner and vice versa. Furnaces are only for heating your home. You can buy a system that does both, however, like a split system or a heat pump (yes, heat pumps cool, too).