What does a furnace do for AC?

Author: Leonora Parker II  |  Last update: Sunday, June 22, 2025

Throughout the year - even during warmer months - a furnace circulates conditioned air around your home. But even beyond that, your air conditioner can't work without a furnace. A furnace houses two components that your air conditioner relies on: the evaporator coil and the blower motor.

Does my furnace have anything to do with my AC?

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.

Does the furnace control the AC?

Your furnace and air conditioner are stand-alone components of your HVAC system. Both your furnace and your AC use ducts and vents to circulate air throughout your home. These systems are tied together because they use the same infrastructure. However, they still operate independently of each other.

Can an AC work without a furnace?

The outdoor condenser and compressor, indoor fans, and evaporator coils cycle refrigerant and draw hot air inside while releasing heat, then draw cooled air back through your vents. In other words, your central air conditioning system is independent of your furnace.

Should the furnace be on or off for the AC?

The only time you wouldn't want to turn off your furnace in the summer is if you have a central air conditioning system. In that case, the AC actually uses the furnace to help circulate cool air through your home, so your furnace will still need to be on to help out with this vital function.

How A Gas Furnace Works (Animated Schematic)

Is it OK to switch between furnace and AC?

A lot of our customers ask us if it's bad to switch back and forth between their heater and AC, and the answer is no, as long as you're doing it correctly.

Why does furnace run when AC is on?

Incorrect Wiring

If you recently had a new HVAC unit installed, the technicians may have incorrectly wired your new system. This incorrect wiring could be causing your air conditioner and heater to come on at the same time. This may also be the case if you replaced your thermostat recently.

How do furnace and AC work together?

The air conditioner will sit outside the home cooling while the furnace works inside the home to heat with fans and coils. Both systems use your home's ductwork and vents to transport warm and cool air. Alternatively, a heat pump and an air handler might be paired together to form a complete system.

Does AC run through a furnace filter?

Even though the furnace is not producing any heat while operating the a/c, it still delivers the cold air throughout your home with the same blower, and passing through the same air filter. This is why, regardless of the season, you should regularly change your air filters.

How much is a new furnace?

Ask twenty professional HVAC contractors the question, “How Much Does A New Furnace Cost?” and you'll probably get the same answer... “It depends.” On average, the cost of a new furnace can range from $2,000 - $14,2001. However, factors like furnace efficiency, type, size, and much more can impact this range.

Why is AC not blowing cold air?

First, check your filters and coils for dirt and debris that may be impeding airflow. Once you've cleaned the filters and coils, run the air conditioner with just the fan so that the ice accumulation can melt off. If the AC still doesn't blow cold air, it could be that refrigerant levels are too low.

Does central air use a furnace?

A central air conditioning system uses the forced-air system within your home to deliver cooled air, making use of the vents, plenums, and ducts to provide conditioned air. The central AC system is independent of your furnace, using an outdoor unit that is not connected to the furnace at all.

How do I switch my furnace to AC?

The most important and most obvious step in switching from your furnace to your A/C is to turn off your furnace. Most modern heating systems can be turned off straight from the thermostat, but if you have an older model you may have to turn off the gas supply.

Will AC work if furnace is broken?

However, the furnace and AC are two distinct appliances that run independently. Because of this, it's unlikely that your furnace and air conditioner will break down at the same time. Therefore, replacing the malfunctioning appliance and keeping the other one if it is still working well may make sense.

Does HVAC need furnace?

HVAC stands for heating, ventilation and air conditioning systems. This system is responsible for heating and cooling your home and includes products like furnaces, air conditioners, heat pumps as well as ductwork, thermostats and other home comfort controls.

Are AC and furnace on the same breaker?

If the home includes an electric furnace, that unit will also have its own dedicated breaker. Issues such as low airflow due to a clogged air filter, obstructed air vents in rooms, a failing blower motor, or internal electrical defects inside the unit may be the cause of breaker trips.

Can I run my AC without a furnace filter?

The short answer: You can get away with running your AC without a filter for a short period of time. However, doing so for longer than 6-8 hours can hurt your system and decrease your home's indoor air quality.

Does my furnace filter affect my air conditioner?

Besides causing an inefficient, poorly functioning furnace, a dirty air filter can also damage your air conditioning system beyond repair.

Do the furnace and air conditioner use the same filter?

While many people refer to air conditioning and furnace filters as if they're different, this is not the case. Your furnace and your air conditioning system use the exact same filter, so there's no need to worry about purchasing separate filters for each piece of equipment.

Can a furnace cool a house?

You might be surprised to learn that your furnace may be used to cool your home even if you do not have an air conditioner. Your home will not cool as much as with air conditioning but some is better than none.

Can a furnace and air conditioner be one unit?

A packaged unit is an “all-in-one system” that can provide both cooling and heating from a single cabinet. The cabinet system can be installed at ground level, in a crawl space or on a rooftop.

How much is an air conditioner and furnace combo?

The cost of a new HVAC system together costs $7,500 on average, usually somewhere between $5,000 to $12,500. This can end up being cheaper than replacing your AC and Furnace separately over time. Replacing your AC and furnace at the same time will enhance the performance of both while consolidating labor costs.

Why is my house so hot even with AC on?

Insufficient insulation: Without adequate insulation, conditioned air will escape through gaps and cracks in walls and ceilings, leading to temperature fluctuations that create hot spots.

How do a furnace and AC work together?

Air conditioners and furnaces work together to keep the air in your home at a manageable temperature. In the winter, your furnace heats the air in your home, while the AC blower circulates works to circulate that air throughout the home.

Should the outside fan run when AC is on?

The short answer: Definitely not. (Unless you have manually engaged your outside fan to run constantly, but it shouldn't be running for hours on it's own.) If your HVAC is functioning correctly, it should keep your house cool by cycling on for 15-20 minutes at a time—with distinct pauses in between each cycle.

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