Stay Comfy Blog

Do I Need a Furnace to Run My AC?


This is a question asked by many, especially when it comes time to replace your furnace or air conditioner. Do I need a furnace to run my AC? The answer is often “yes,” here in Minnesota, but it depends.

For Central Heating and Cooling Systems

The relationship between your AC and furnace is a close one if you have a central heating and cooling system – also known as HVAC. They work hand in hand, so if you upgrade one part of the system – let’s say, the air conditioner – and decide to put off upgrading the other – the furnace – you may notice an effect in efficiency, meaning that it won’t be as efficient as it could be if you upgraded both at the same time. 

According to home advisor website,, “mixing old and new technology can decrease system performance. By replacing just one part of your overall HVAC system, you effectively lower the performance of both systems. When you couple a new, highly efficient system with an older system, the components don't ‘match,’ and you won't be utilizing the new technology to its full potential.”

In a central heating and cooling system, your AC and furnace use the same ducts to get you the warm or cool air,and it’s the blower in the furnace that drives the air for both heating and cooling. Typically, the same thermostat controls the temperature, and the same vents and grilles let that conditioned air through to bring you comfort in your home. Because of this symbiotic relationship, you can see why the various parts of a traditional HVAC system in Minnesota do in fact rely on the each other, or the same parts to work.

For Other Systems

However, not all air conditioners rely on that relationship as part of a larger HVAC system. Some homes use room air conditioners, where the ACs are installed in a window or wall opening. This is often seen in smaller spaces, like apartments, condos, guesthouses, or stand-alone rooms that need a little extra comfort.

It also depends on climate. Many places along the ocean use the natural winds coming off the water for cooling comfort, but they may need to supplement with a room AC for those very steamy days when they need extra cooling. Since those warmer climates don’t need a furnace to keep them warm, the most affordable and efficient option is a room air conditioner or a ductless mini-split AC.

In climates that have both heating and cooling seasons, but are more moderate than the severe weather swings of Minnesota, you will notice homes use heat pumps more often. According to the Department of Energy website, heat pumps are a very energy-efficient alternative to furnaces and air conditioners. 

The website says that heat pumps work like a refrigerator – they use electricity to move heat from a cool space to a warm space, making the cool space cooler and the warm space warmer.

“During the heating season, heat pumps move heat from the cool outdoors into your warm house and during the cooling season, heat pumps move heat from your cool house into the warm outdoors. Because they move heat rather than generate heat, heat pumps can provide equivalent space conditioning at as little as one quarter of the cost of operating conventional heating or cooling appliances,” the Department of Energy says.

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