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Do I Need to Replace My AC and Furnace at the Same Time? Pros & Cons

Sometimes it does make sense to replace your furnace and air conditioner. Sometimes it doesn’t. In this article, we break down scenarios for each.

Do I Need to Replace My AC and Furnace at the Same Time? Pros & Cons

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Roger Bakies


February 28th, 2021

Whether it came as a surprise or you’ve been planning for a while, eventually you’ll have to replace your HVAC equipment. It’s essentially the circle of life for air conditioners and furnaces.

But hang on -- did your HVAC contractor just say you should replace both your air conditioner and furnace?

Sometimes this is the case. But while there are situations where you need to replace both your air conditioner and furnace, there are also situations where replacing both doesn’t make sense. I’m here to walk you through both.

I’ve worked in the HVAC industry for over 30 years. Throughout my career, I’ve seen air conditioners and furnaces from every possible angle. I’ve installed and serviced them as a technician. Now, I help educate homeowners so they can make well-informed decisions for themselves and their homes. I also help our customers find the best air conditioners and furnaces for their homes.

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At Fire & Ice, we believe that our homeowners can make the best decisions when they have access to the best information.

In this article, we’ll discuss scenarios when you should replace both systems and when it may not make sense to replace both. We’ll also weigh the pros and cons of each option.

By the end of the article, you’ll have the information you need to decide which is best for you and your home.

When You Should Replace Both Your Air Conditioner and Furnace

It’s not always the right time to replace both your air conditioner and furnace. But in some situations, replacing both means that you can get more out of your HVAC system.

Replacing both your furnace and your air conditioner can also be more cost-effective.

On its own, a replacement air conditioner can cost between $4,350 - $12,095. A lone replacement furnace can cost between $3,000 - $7,600. (Both of these ranges include the cost of the equipment, labor and other fees.)

But you can save on labor expenses and fees when you replace both systems. Some HVAC contractors also offer incentives if you replace both your air conditioner and furnace.

The following are scenarios where you may need to replace both your air conditioner and your furnace at the same time:

  • When your existing HVAC equipment isn’t the right size
  • When you upgrade your air conditioner
  • When you want to improve your comfort
  • When you want to sync both warranties

A furnace and an air conditioner.

When Your Existing HVAC Equipment Isn’t the Right Size

When we talk about the “size” of your HVAC equipment, we’re talking about its power.

But this is one instance where an overly powerful system is a bad thing. In order to properly heat and cool your home, your furnace and air conditioner must be the right size for your home.

Sure, your furnace or air conditioner can heat or cool your home even if it’s the wrong size. But if your system is too big or too small for your home, it’ll experience increased wear and tear that can take a toll on its life expectancy and performance. Improper sizing can shorten a system’s lifespan by as much as 5-10 years.

Replacing improperly-sized equipment can also address high utility bills, temperature spikes, and hot and cold spots. However, other factors can also account for these issues.

To properly size your equipment, your HVAC partner must perform a load calculation. A load calculation can also help determine whether your existing equipment is the right size.

For more information on load calculations, check out the video below. While it focuses on air conditioners, we also use this type of load calculation to determine the right size for your furnace. This is the process that your HVAC partner should use to check that your existing system is the right size for your home and your needs.

When You Upgrade Your Air Conditioner

Three air conditioner upgrades may require you to replace both your AC and furnace:

  1. A communicating air conditioner
  2. A variable-capacity air conditioner
  3. A two-stage air conditioner

A communicating air conditioner uses sophisticated learning technology to hyper-customize your cooling solution to your needs and lifestyle.

While a non-communicating thermostat signals your furnace or air conditioner to turn on, communication goes both ways in a communicating system. Communicating systems like the Trane XV20i “talk” with your thermostat. This allows your thermostat to closely monitor and adjust your system’s performance.

To truly benefit from a communicating air conditioner, you should generally have a fully communicating HVAC system. This includes a communicating thermostat and a communicating furnace like the Trane XC95M.)

An air conditioner.

But whether your air conditioner is communicating or not, it relies on your furnace to keep you cool in the summertime. Even when it’s so hot out that your furnace is the last thing on your mind, one part of your furnace keeps running.

That part, the blower motor, is responsible for circulating air throughout your home.

But what does this mean for replacing your air conditioner and furnace? There are different types of blower motors. When you upgrade your air conditioner, your blower motor must be able to support your new air conditioner’s cooling output, also called staging. Otherwise, your upgraded air conditioner may not work to its full extent.

There are a few options for air conditioner staging. But compatibility typically only becomes a concern if you upgrade to a variable-capacity air conditioner or two-stage air conditioner. (Generally, compatibility isn’t an issue with single-stage air conditioners.)

A variable-capacity air conditioner can have up to 700 adjust its output to better maintain the temperature in your home. This can cut down on energy costs, temperature spikes, and hot and cold spots. 

But if you don’t have a variable-speed blower motor, a variable-capacity air conditioner won’t be able to reach its full potential due to incompatibility.

But there’s another reason why your upgraded air conditioner may not work with your existing furnace: the manufacturer-specific technology.

In other words, if you purchase anything more than an entry-level air conditioner, you generally need to purchase a compatible furnace from the same brand.

Even though air conditioners and furnaces work similarly regardless of their brand, manufacturers do build HVAC equipment with their own patented components. In many cases, you’ll likely need to purchase both systems from the same brand.

But how do you know two systems are compatible? Air Conditioning, Heating & Refrigeration Institute (AHRI)’s certification directory can help homeowners identify compatible, or “matching,” systems.

You can search specific models and brands through AHRI’s directory to determine which HVAC systems match.

Matching systems also ensure that both systems are covered under warranty. If you don’t have compatible systems, your warranty may not be valid.

When You Want to Improve Your Comfort

Whether you’re due for a new air conditioner or a new furnace, replacing both could make sense if you want to improve your comfort year-round.

Components like multi-stage equipment and variable-speed blower motors can help improve your comfort. These components can also address problem areas that your current system struggles to overcome. This could result in fewer temperature spikes and fewer hot and cold spots throughout your home.

Your HVAC partner should be able to help you determine how best to address these problem areas.

At Fire & Ice, we call these problem areas “comfort concerns.” Check out this article to learn how we use comfort concerns to customize our customers’ HVAC systems.

Singe-Stage | Two-Stage | Variable-Capacity

When You Want to Sync Both Warranties

Syncing the warranties for both your air conditioner and furnace has a few benefits, such as:

  • Less guesswork: Syncing your warranties takes away some of the guesswork. In some cases, you may not know or remember whether your existing system is under warranty. When you replace both your furnace and air conditioner, you know both systems are warrantied for the same amount of time.
  • Peace of mind: If either system needs repairs, neither the manufacturer nor a contractor can blame the issue on an un-warrantied system. Manufacturer warranties typically don’t cover labor costs. But if both systems are under warranty, this can save you money on the repair.

When You Don’t Have to Replace Both Your Air Conditioner and Furnace

Although there are benefits to replacing both systems, this may not always be the case.

In some cases, waiting to replace your system can mean that you’re making the most of your investment. After all, today’s furnaces and air conditioners typically last 15-20 years -- or longer. And if you don’t really need to replace part of your HVAC system, you’ll be able to put your hard-earned money toward more pressing issues.

However, even if you wait to replace part of your HVAC system, you will need to replace it eventually. And you may not always be able to choose when in the future, especially if it breaks down or needs a costly repair.

The following are scenarios where you may not need to replace your air conditioner and furnace simultaneously:

  • When you replace your furnace
  • When your existing furnace is compatible with your replacement air conditioner
  • When your other system is newer or meets your needs
  • When you don’t want to replace both systems

A furnace.

When You Replace Your Furnace

As I mentioned earlier, your air conditioner needs your furnace, but your furnace doesn’t need your air conditioner. In other words, when you replace your furnace, you don’t necessarily need to replace your air conditioner too.

In fact, a new furnace may even be able to boost your existing air conditioner’s performance.

If your new furnace has a variable-speed blower motor, it’ll improve air circulation throughout your home year-round. This helps distribute conditioned air throughout your home, which can result in more consistent temperatures throughout your home (even on muggy upper floors).

For more on this, check out this article on how different types of furnaces can affect your home.

However, If you don’t replace your air conditioner and furnace at the same time, you should always look forward.

As we discussed earlier, your furnace and air conditioner must be compatible. If you only plan to replace your furnace, you should evaluate your goals for your home. This is especially important if you plan to stay in your home long-term -- or at least for the rest of your existing air conditioner’s lifespan.

If you plan to upgrade your air conditioner in the next decade or so, you may want to consider a compatible furnace now. (We discuss the importance of compatibility earlier in this article.)

While you can always replace your furnace later, you can save money overall if you plan for the future now.

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When Your Existing Furnace is Compatible with Your Replacement AC

If your existing furnace and your new air conditioner are compatible, you don’t necessarily need to replace both systems.

This is usually the case when you replace your air conditioner with a similar model.

A new furnace could boost your system’s efficiency. But you may not need to replace your furnace if you don’t have high energy costs.

While you will need to replace your furnace eventually, you have more flexibility in this case. Your furnace sets the pace for your air conditioner. Even if you plan to upgrade your furnace in the next decade or so, you likely won’t need to replace your air conditioner (unless you upgrade to a communicating system, as we discussed earlier).

It’s still a good idea to plan for the future, though. If you do plan on upgrading your furnace eventually, talk to your HVAC partner about some of those options now. This can help you decide which air conditioner will serve you best long-term.

When Your Other System Is Newer or Working Fine

If you’re only replacing one system and your other system is newer or meets your needs, you don’t necessarily need to replace both systems.

As a guideline, we usually don’t recommend replacing systems that are less than 10 years old (as long as they can meet our customers’ needs).

The most important factor here is whether or not your system can continue meeting your needs. Newer equipment can help address problem areas, including issues with temperature, air quality and energy costs. But if you don’t have any problem areas, then your existing system is likely capable of meeting your needs.

If you do have problem areas that you’d like to address, bring those concerns to your HVAC partner. The best time to address issues that you have with your current system’s performance is when you’re replacing existing HVAC equipment.  

A technician speaking with a customer.

When You Don’t Want to Replace Both Systems

Ultimately, whether you replace both your air conditioner and furnace or only one system is your decision.

Replacing both your air conditioner and your furnace at the same time has its benefits. But when you know those benefits, as you do now, you can make the best decision for you and your home.

If replacing both systems doesn’t align with your goals or needs, then you may not necessarily need to replace both your air conditioner and your furnace.

Making the Right Decision for You

Even if you don’t have experience with HVAC equipment, you know your home best. Your HVAC partner can help educate and advise you, but you have to live with your HVAC system.

Some HVAC contractors across the country profit off of their customers’ inexperience. The best way to avoid that is to do what you’re doing right now: educating yourself.

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At Fire & Ice, we believe in educating our customers and fairly presenting all the options -- whether we benefit from them or not.

If you’d like to replace your furnace, air conditioner or both, we’d love to help!

We offer free in-home estimates to ensure we know how to meet your needs. If you’re still uncertain about whether or not you should replace both systems, an in-home estimate is a great time to have that conversation.

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