How Long Will My Furnace Last?

We all want certainty with major purchases. Will my car last 70,000 miles or 200,000 before it starts to break down? Will my windows continue to prevent major air leaks for the next 10-20 years?

And will my furnace or air conditioner work efficiently for the next two decades of living in a home?

We’re going to focus on the furnace question today. We tell many of our customers that 15-20 years is a reasonable estimate for a properly installed and well-maintained system, and it is. But that’s an estimate, and a lot goes into that assumption. Just as importantly, a lot can happen to reduce that expectation.

Fortunately, this is where you and your HVAC partner come in. There’s no guarantee of a particular year total before you start to get hit with repairs, but there’s a lot you can do to avoid the worst of it.

How Ductwork Can Affect HVAC Lifespan

Say you have improperly sized air ducts. This happens more than you might expect, and the result will be 10%-30% higher utility bills for the life of your system. Equipment needs to work harder and will break down sooner as a result.

Seventy percent of all systems have ductwork or airflow issues. The furnace will struggle and eventually wear out quicker if there’s not enough air supply going out or not enough return air coming in. Maybe the previous homeowner put a big filter in the system, which restricts airflow everywhere in the system.

The Difference Between Old and New Furnaces

“They don’t make ‘em like they used to.”

This phrase is true in HVACe. But it might not be true in the way you’re expecting.

We visit households with furnaces that are still working after 25 or even 30 years! If we stopped with that fact, it might seem like the 15-20 year expectation for modern furnaces is worse. After all, 30 years is better than 20. Right?

There are two big factors to keep in mind that will adjust this calculation:

1. Since older systems were generally basic, single-stage units without many additional options, it was often cheaper to replace major parts for them rather than replace the entire system. So that 30-year-old furnace probably has none of the major components it was installed with.
2. Modern systems are more efficient. Sometimes a lot more efficient. They have more options, more built-in safety precautions, will provide better comfort for your home, and will often lower your utility costs considerably.

Take those two together and the calculation shifts quite a bit. Sure, you could squeeze 30 years out of some systems if you’re lucky, but you probably don’t want to, because you’re sacrificing comfort and money in the long run. A system that’s “running fine” might actually be a money pit. But if that’s all you’re used to, it can be misleading.

High-Efficiency Furnace vs. Low-Efficiency Furnace

Customers tend to believe that the higher-end stuff breaks down quicker. You have the old tried-and-true technology of a low-efficiency single-stage unit. That’s been around for years. So you think, why would I get a two-stage or a variable speed? It’s true that the more parts you have, then the more chance you have of something going wrong.

A high-efficiency furnace does have two heat exchangers as opposed to one. Does that increase the chances of something breaking down? Sure.

But I tend to believe that a variable-speed furnace will last longer. The blower motor would last longer because it will run at a slower, consistent speed while it’s on the first stage. The motor will not turn on to 100%, then turn off as much.

Instead of going from zero to one-hundred, it’s like, if you were going to leave your car running at a very low speed compared to if you were going to start and stop your car every ten minutes. Which one wears out sooner? The second scenario.

The Importance of Furnace Maintenance

So I just told you I’ve seen furnaces that are 30+ years old, and that’s true. But the opposite is true as well: we’ve had to replace furnaces that are under 10 years old.

The biggest reason for this is lack of maintenance. Actually, I’ll go a step further: sometimes the only reason for this is a lack of maintenance. Think of it like your car; if you forget the oil change, it will run ok for a while, but eventually you’ll run out of luck.

And just like your car, if a system is running, that’s not enough to say that it’s running well. That’s the biggest thing maintenance provides. But it also goes beyond that.

At some point, something within your system will start to break down. This is inevitable, regardless of how well-maintained it is. From a homeowner’s perspective, this will usually seem sudden. “It was working fine and then just stopped” is a phrase we’ll hear a lot.

The thing is, equipment that’s running fine doesn’t just break down out of nowhere. There are always signs leading up to it. These issues are usually detectable months or even years in advance. You often won’t be able to see the signs just by running your system, unless there’s a loud noise or obvious drop in heat being produced. But for someone inside the system, inspecting and adjusting parts for optimal operation, they’re going to be able to see a lot more.

Static Pressure, Or Running a Marathon In a Mask

To show what I mean, here’s an example: Static pressure is basically when your blower motor (which moves air through your system) has to work harder than it should to move the proper amount of air through a home.

And what can cause high levels of static pressure? Let’s count:

1. Clogged filter that isn’t allowing air to move through it smoothly
2. Overly large filter for the system that has the same effect as a clogged filter on airflow
3. Gunk in the blower motor itself, which makes functioning more difficult
4. Buildup of dirt, dust and small objects in your ductwork. Have your kids ever dropped something down an air vent? That’s affecting airflow and can start to collect dirt and dust to make the problem even worse.
5. Ductwork that’s too small. Let’s say your ductwork isn’t wide enough. That creates backups of airflow in the system. And if the ductwork is too large? The fan is working overtime just to get the air moving through it.
6. If burners in the furnace aren’t all lighting, the fan may have to run for longer to spread heat evenly.

To put it in different terms, imagine draping a towel over your head that covers your mouth. Now try to run a marathon. How much harder will it be with that towel lodged in your mouth? Your breath in this scenario is the blower fan in your furnace, and it’s working overtime because it’s clogged up.

Most or all of these are things regular service can prevent. And, to bring us back to our central question of lifespan, it can easily be the difference between having your furnace for 10 years or 20 years.

The Effects and Neglect of Filters

That static pressure from a dirty filter is suffocating your furnace because it’s not able to get enough airflow. Your furnace has to work harder. A restrictive air filter has the potential to turn a 16-SEER system into a 10-SEER system.

(SEER stands for Seasonal Energy Efficiency Ratio. It’s calculated by the ratio of heat produced by a furnace, divided by its energy usage in watt-hours. This ratio is calculated over the length of a typical heating season. The higher the number, the higher the efficiency.)

If you hold a filter up to a light, you should see light through it. You hold a dirty filter up to a light, it’s basically like a piece of cardboard. Air is working a lot harder to get through there.

Some filters are one-year, and some are designed to be replaced quarterly. Others, like a standard one-inch filter, should be replaced every one or two months. You should be changing your filter consistently, regardless of the season.

A dirty filter can lead to a lot of things besides health concerns. A dirty filter leads to dirt in the blower motor and other components. Dirt and debris that isn’t picked up by a filter can lead to a clogged or a dirty coil, which can also restrict your airflow.

Does the Size of Your System Matter?

We’ve talked in the past about the Manual J Load Calculation, which should happen any time you get an estimate for a system replacement. Basically, it determines what power level (referred to as “size”) a furnace should be to properly heat your home. This calculation is very important to the life of your furnace.

If Your System Is Too Small

If the power of the system isn’t enough to heat your home, this is bad for some obvious reasons. If you have a split-level home, the second story is probably never going to heat up as much as you want it to. Additionally, your furnace is going to have to run almost constantly when it gets colder, to keep up with the temperatures. More run-time equates to more stress on the equipment, and more money spent each winter.

If Your System Is Too Big - Short Cycling

A system that’s too powerful is a big problem, but it’s less obvious why. After all, if your system has the power to heat your home in 20 minutes, wouldn’t 15 minutes be better?

But imagine a too-large system pumps a bunch of warm air into your home quickly. The thermostat is going to detect this and will signal for the heater to shut down. But when the air is pumped into the home too quickly, it doesn’t have a chance to properly mix with the colder air.

So if your thermostat is set to 72 degrees, the thermostat might detect 72 degrees momentarily. But as soon as the air mixes evenly with all air in the home, it will drop to 71 or 70. Then your thermostat will signal for the furnace to turn on again.

This can happen in as little as a minute. At this point, hopefully you’re starting to see the issue. The furnace will kick on, then off, then on, then off, and so on. This is known as short cycling.

A furnace that kicks on and off 20 times an hour is going to break down a LOT sooner than one that only turns on 2-3 times. And this will only happen if your HVAC system is too powerful for the home it’s in.

Does Furnace Brand or Model Matter?

Does the furnace brand matter? Sort of. Some people have a preferred brand, but the fact is, several well-known brands make quality HVAC equipment. We’re partial to Trane and Carrier here at Fire & Ice, which is why we’re a dealer for those brands. But if you have a Goodman, Lennox or another major brand, you’re probably going to be in decent shape as long as it’s installed properly.

The bigger difference is going to be in the sophistication of the model. All brands have lower-end and high-end equipment. Not surprisingly, some of the lower-end equipment has a shorter expected lifespan.

That doesn’t mean it isn’t good. It can absolutely still be a major upgrade for some homes, and can last for many years. But you’re getting what you pay for in terms of long-term expectations.

So a “builder grade” entry-level furnace probably isn’t going to last as long as the high-end rocket ship that has a bunch of features and options (at least on average). But that higher-end model is going to save on utilities, provide more control and comfort, and will likely last longer.

RELATED: How Much Does a Furnace Replacement Cost?

This article isn’t a buyer’s guide, but knowing your budget and setting expectations accordingly can be important when approaching the installation of a new furnace.

Why Your Air Conditioner Matters

Wait, why are we talking about air conditioning? One important reason: your blower motor.

The blower motor controls airflow for both heating and cooling in your home. Everything we said earlier about dirt buildup, clogged filters, and proper sizing applies to the air conditioning side as well. And then it can affect the furnace.

So, for example, if your air conditioner was installed at a different time and was improperly sized, it can short cycle and burn out the blower motor just like the furnace can. Then when it gets to the colder months, you’re using an overworked fan.

If your air conditioner is being maintained, is properly sized, and is as efficient as the furnace, you’re in good shape. But neglecting one is the same as neglecting both.

The Final Word on Furnace Life

So how long will your furnace last you? Hopefully by now you realize that a lot goes into that. The best HVAC company in the world can’t guarantee a long life for your system unless you’re taking the steps to ensure you get the most out of it.

But the good news is, you have that power. If you’re looking for the best contractor to work with, check out some of the resources below to prepare yourself.

And if you’re ready to have someone take a look at your current system, hit one of the buttons below and we’ll be glad to come out for a free replacement estimate or service visit. We’re looking forward to meeting you!

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