When Do You Need to Replace a Furnace or AC Unit 

No furnace or AC unit lasts forever and deciding when to replace yours can prevent major financial strain. How long does a furnace last until it’s time for a replacement? What about an air conditioner?

The average lifespan of a furnace is 20 to 30 years whereas an air conditioner lasts anywhere from 10 to 20 years. If the two units are aged about the same, you might decide to upgrade them both in one fell swoop.

In today’s guide, we’ll tell you everything you need to know about replacing your major HVAC units, including when to do it, how much it costs, and how to find a good replacement. Make sure you keep reading, as we have lots of great info ahead! 

How Long Does a Furnace Last?

Throughout the winter, you’ll rely heavily on your furnace to keep your home warm and toasty. 

Your furnace uses propane or natural gas. A burner within the unit ignites the gas, generating flames. These flames warm up a metal heat exchanger as well as a flue, which allows exhaust to exit.

Through the heat exchanger, heat travels and mixes with air, coming out of your home’s return vents as warm air.

Furnaces can last for a surprisingly long time, anywhere from 20 to 30 years and sometimes longer. 

6 Signs It’s Time to Replace Your Furnace

Is your furnace getting up there in years? The following signs might be familiar to you. They’re all indicative that your furnace is on its way out and will soon need to be upgraded to a newer model.

The Furnace Flames Burn Yellow

The next time your furnace turns on, be there to watch it. What color flames is your furnace producing?

If you answered blue, then your furnace might still have a few more years in it left. For those who said yellow, you must get a new heater immediately.

Yellow furnace flames often mean that your furnace is making carbon monoxide. If not, then the flames could be bright yellow if the furnace isn’t properly combusting or if a gas leak has occurred. 

It’s not safe to keep your furnace for even another day in that situation.

Your Energy Bills Get Higher and Higher

You know what a normal month of spending on utility bills looks like. For a long time though, your utility bills have gotten increasingly higher.

Well, we hate to break it to you, but your utility bills will keep climbing until you replace your furnace. The unit is no longer efficient enough for your home.

You’ve Spent Thousands on Repairs

Your furnace seems to break at least three times every winter. It’s been like this for years.

At this point, the furnace has become a black hole. All the money that you’ve sunk into it could have been used for buying a new furnace, possibly even two or three times over! 

The Furnace Register Is Sooty

The last thing you want is soot lingering throughout your home, but the older your furnace gets, the likelier that is to happen. The air in your home will become very dry and dirty.

That kind of air is a nightmare for those with allergies and/or asthma to breathe in. Even those with healthy lungs will notice the dip in air quality. 

If you check your furnace grille or register and you see an accumulation of soot, that explains why the airflow of your home is so poor. This problem won’t fix itself though and means you need a new furnace. 

Your Home Temperature Changes a Lot

It’s so strange. Sometimes, it seems like your furnace is working fine. Then, later that same day or the next day, your home is cold. 

You keep pushing up the thermostat, but your furnace does not react in kind. 

Once your furnace reaches about the 15-year mark, it can no longer keep up. Even though the heating demand of your home hasn’t changed, the unit will struggle to create consistent heat and then maintain it. 

You need a new furnace to fix this problem. 

The Furnace Runs Very Loud 

The last sign that you need a new furnace is that the HVAC unit can’t run quietly. 

If it’s clicking, that’s due to a faulty ignitor or flame sensor. A humming sound is usually because the furnace blower motor is breaking down. 

Screeching sounds are also indicative of something being wrong with the furnace blower motor. 

Rattling happens if the ducts around the furnace loosen while popping occurs when your furnace struggles to maintain a consistent temperature.

How Long Does an Air Conditioner Last?

Ice cream, sunglasses, flip-flops, air conditioning. No summer is complete without AC, as it makes those sticky warm days that much more bearable. 

How does an AC do its thing? If yours is central air conditioning, then the unit has an evaporator that eliminates humidity and heat with refrigerant and cooling coils. 

The fan or blower sends air across the evaporator, allowing cold air to spread throughout your home. In the meantime, a condenser with hot coils sends all the warm air outside so your home stays cool. 

The other components of the AC are a compressor (for transferring refrigerant as needed), another fan, a filter to keep the air clean, and a thermostat to control the temperature.

With so many components, it’s no wonder that central air conditioning doesn’t last as long as your average furnace. The typical AC lifespan is 10 to 15 years. 

6 Signs It’s Time to Replace Your Air Conditioner

Is it time to say farewell to your air conditioner and buy another one? The following signs will let you know. 

Your Utility Bills Keep Going Up

As was the case with a faulty furnace, if your air conditioner is long past the point where it should have been retired, then you’ll see it in your utility bills month after month.

Your aged AC is straining to do the things it once did with ease. It needs more electricity, which is why you end up spending so much cash every 30 days.

The cooling output of your air conditioner doesn’t increase though, which means you’re constantly standing at your thermostat trying to get your home to a consistently cool temperature. 

You’ve Lost Track of How Much Money You’ve Spent to Repair Your AC

Speaking of money out of your pocket, you don’t even dare calculate what you’ve spent to get your AC in working condition time and again. 

In the dead heat of summer, you don’t want to go a single day without working air conditioning. You pay what you have to so your home can stay cool, and your family isn’t miserable. It’s as simple as that.

As your furnace can become a black hole for you to sink money into, so too can an old air conditioner. You have to know when to say enough is enough and finally upgrade the unit. 

The Air Conditioner Smells

Air conditioners don’t produce the best-smelling air, but the scent should be at least neutral and certainly not offensive. 

If you smell very stale air or air that’s burning or smoking, then something in your central air conditioning is very, very wrong. 

Your AC Makes a Lot of Noise When It Runs

Your air conditioner doesn’t have to run whisper-quiet, but if it’s making all sorts of sounds every time it kicks on, that’s a problem. From chattering to squeaking and grinding, the parts of your AC system are crying out for mercy!

It’s certainly time to consider a replacement at this point. 

Moisture Has Accumulated Around the Unit

It’s normal for the AC to have a layer of condensation on it, but when condensation turns into a puddle, that’s problematic. 

More than likely, refrigerant or coolant is seeping out from your air conditioner, which isn’t super healthy for you and your family to breathe in. Plus, your AC will strain even more since it doesn’t have the full coolant load it needs.

The Airflow and Air Coolness Is Not as Efficient 

The airflow of your AC used to be a cold blast of air that slapped you across the face in the best way possible. It was an amazing way to get relief on a hot summer day. 

Now the airflow of your AC is a lot less, not to mention the unit doesn’t produce cold air at nearly the same rate that it used to. 

While you could get the ductwork or piping repaired, in this case, you’re better off replacing your air conditioner, especially if it’s more than a decade old. 

How Much Does It Cost to Replace a Furnace?

Okay, so you’ve decided you need a new furnace. How much is the unit going to cost you?

According to HomeAdvisor, the national average for a new furnace is $4,667, with a typical range between $2,800 and $6,758. You could pay as much as $10,000 for this project in some cases.

It’s not that furnaces themselves are expensive. You can get your hands on a Goodman gas furnace for as little as $800. Even if you wanted an expensive gas furnace, such as from Rheem or York, you’d pay $2,500.

It’s the installation fees that drive up the costs, as these are valued at $2,400 to $4,300. 

Oil furnaces themselves aren’t too much more expensive. The average cost of one of these furnaces is about $2,500, but installation can cost anywhere from $6,900 to $8,000. 

How Much Does It Cost to Replace an Air Conditioner?

What if you need a new air conditioner instead of a furnace? What is that going to cost you?

HomeAdvisor states that the national average cost for new central air is $5,685 with a typical range between $3,800 and $7,584. You could pay as much as $11,500 for a new AC.

While furnaces are priced by the fuel source, AC costs vary according to the cooling capacity you need, which is represented as British thermal units or BTUs per hour.

Here’s an overview of what you could spend on a new central air conditioner by BTU per HomeAdvisor.

  • $2,500 to $4,500 for an 18,000-BTU air conditioner
  • $3,100 to $5,100 for a 24,000-BTU air conditioner
  • $3,400 to $5,400 for a 36,000-BTU air conditioner
  • $4,200 to $6,200 for a 48,000-BTU air conditioner 

Should You Replace Your Furnace and AC at the Same Time?

Considering the high costs of both a new air conditioner and a new furnace, you might wish to bite the bullet and just buy both HVAC units at the same time. Is this feasible? 

In certain situations, yes! Let’s look at the various instances in which upgrading both your AC and furnace is best.

The Units Are About the Same Age

Although you don’t have to replace a furnace until it’s about 20 years old, if your AC is about that same age too, then it makes sense to buy both units at the same time. 

They’re both on their way out, so if you waited on the furnace, it could break when you least expected it. Then you’d have to spend money at a time that might not be as convenient as it is right now. 

You Want Concurrent Active Warranties

Keeping track of two warranties for your furnace and air conditioner can be confusing. When you replace these units together, you know that their warranties will both begin on the same day. It’s even better if the duration of the warranties is the same! 

You Want a More Comfortable Home All Year Long 

It’s a wonderful feeling when your heater or air conditioner works well because it’s brand-spankin’-new, but it does leave you feeling bad the other half of the year when the other unit underperforms.

Should you push ahead and replace your air conditioner and heater at the same time, your home will be comfortable and efficient no matter the season! 

Tips for Replacing Your Furnace or AC Unit

Between the expense, the time it will take for an installation team to get everything set up, and the adjustment of using a new furnace or AC, you want to make the replacement process as smooth as possible. 

Here are some tips that will allow you to do just that. 


The moment your furnace or air conditioner begins making loud banging sounds or the unit isn’t producing the requisite amount of heating or cooling, it’s time to start setting money aside.

Ideally, you’ll already have a savings fund for emergencies such as these. In that case, then count what you have and calculate how much more money you need to afford a new HVAC unit.

Remember, you can’t only factor in the cost of the furnace or air conditioner, but installation and delivery fees as well. 

Prioritize Energy Efficiency

These days, it’s practically impossible to buy a new furnace or air conditioner and not have it be energy-efficient. 

Even still, you should spend some time researching to determine how much energy your current HVAC units use and how much you would like the new units to use.

You should also know your basic heating and cooling outputs as well as the square footage of your home. All this information will make it easier to shop for a new furnace or air conditioner. 

Look into Incentives and Rebates

We’ve established that paying for an AC or furnace is not exactly cheap. You don’t necessarily have to shoulder the burden alone.

If your new HVAC units are exponentially more energy-efficient, then you could be eligible for incentives or rebates as offered by your city, town, or state. 

Usually, the way the incentive or rebate works is that you initially pay the full cost for a new air conditioner or furnace. After you prove that you meet the terms of eligibility, you’ll receive a certain amount of money off your purchase.

You’re essentially recouping the money back, and that’s always nice! 

Compare Quotes

The best part about planning for a furnace or air conditioner replacement before you absolutely need one is that you have the time to compare your options. 

Request several quotes from manufacturers and then assess them side by side. Don’t necessarily choose the cheapest quote, but the one that most closely slots into your budget. 

Other Household Maintenance to Consider

Don’t forget other household maintenance items to keep track of. It’s always best to replace big appliances before they brake on your, so you’re not scrambling for a repair person at 5:00 on a Sunday evening.

Check out our other articles, 9 Reasons to Replace Your Hot Water Heater Before it Fails and 5 Reasons Your Swamp Cooler Keeps Burning out.

Final Thoughts

If it’s been at least a decade (or in the case of a furnace, two decades), it’s time to start thinking about buying a new air conditioner or furnace. Although these units are not cheap to replace, the energy efficiency of newer HVAC will lower your utility bills every month! 


Geoff Southworth is the creator of RealEstateInfoGuide.com, the site that helps new homeowners, investors, and homeowners-to-be successfully navigate the complex world of property ownership. Geoff is a real estate investor of 8 years has had experience as a manager of a debt-free, private real estate equity fund, as well as a Registered Nurse in Emergency Trauma and Cardiac Cath Lab Care. As a result, he has developed a unique “people first, business second” approach to real estate.

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