How Long Do Furnaces Last? Do You Need A Furnace Replacement Now?

Furnaces are HVAC heating units that usually last very long. How long do furnaces last?

Here’s the short answer:

Furnaces can last from 5 to 30 years. That’s quite a broad furnace lifespan range. Most furnaces will last anywhere from 10 to 20 years. Most homeowners would like their furnace to last 30 years and would hate if they would have to replace a furnace after merely 5 years.

how long do furnaces las
Furnaces last, on average, for 10 to 20 years. If you have a 30-year-old furnace, you might think about replacing it will a new unit.

Here’s one thing that’s even more important than knowing how long should a furnace last:

Do You Need To Replace Your Furnace Now?

If your furnace is 20 or even 30 years, you need to consider replacing your furnace. Signs that your furnace needs to be replaced include:

  • Furnace is producing loud noises while running.
  • Temperature is not as stable as it once was. You may experience temperature fluctuations throughout your house.
  • You see soot accumulating near the furnace’s register.
  • Higher heating expenses, or high repair expenses, or both.
  • Furnace flames that were once blue are now turning into yellow flames.
    how to know if you need a furnace replacement
    A healthy furnace has clear blue flames. If you see yellow flames, that might be one of the most obvious reasons for replacing a furnace.

Most homeowners will want to know how to make the furnace last as long as possible (up to 30 years). Even more important is knowing mistakes many of us can make that can reduce the lifespan of a furnace down to 5-10 years.

We have assembled valuable insights into how to prolong how long does a furnace last. Namely, we will look into:

  • 4 ways how to increase furnace lifespan. You would be following these maintenance, sizing, and BLA recommendations in order to keep your furnace functioning at 100% levels for as long as possible.
  • 4 things that decrease the lifespan of a furnace. If you don’t want your furnace to stop working 100% effectively after only 5 or 10 years, you should avoid making mistakes that, frankly speaking, many furnace owners are not entirely aware of.

Let’s start with looking at how to increase the time of how is a furnace good for:

4 Ways How To Increase Furnace Lifespan To 20-30 Years

What is an average life expectancy of a gas furnace? A gas furnace lasts for about 15 years. If you could prolong how long does a gas furnace last, you can save up to about $1,000 per year by not having to buy a new gas furnace.

The same is true for electric, diesel, and oil furnaces. The longer you can keep a furnace going, the more value you can get from the initial furnace investment. Here are the 4 ways to follow to ensure a furnace will last longer than its average lifespan:

1. Size A Furnace Adequately For Your Home (Reduce Wear And Tear)

The primary reason why furnaces don’t last as long as they should is inadequate furnace size. That’s true in both of these cases:

  • Too big a furnace generates more wear and tear.
  • Too small a furnace generates more wear and tear.

How is it possible for a furnace to generate more wear and tear if they are too big or too small?

The reason why too big furnaces don’t last as long are shorter cycles. A furnace that’s too big will turn on and off much quicker than it would normally do. That’s because a large furnace will heat a space rapidly, achieve its thermostat set temperature, and will shut off quickly.

With a quick succession of these short cycles, a furnace goes through up to 70% more wear and tear than necessary (the exact percentage depends on how oversized a furnace is). That also generates 70% more wear and tear. If a gas furnace would normally last for 15 years, 70% of additional wear and tear can reduce its lifespan to below 9 years.

The same lifespan reduction happens if you have a too small furnace. A small furnace is a big home has to stay on for too long. These furnaces will do everything in their power to heat up a home they are unable to heat, running at near 100% heating output all the time.

This may reduce the average life expectancy of a small furnace from 15 years to less than 10 years (depending on how undersized a furnace is).

There is an obvious solution to thing problem: Get the right size furnace for your home. You should consult an HVAC expert about how large a furnace you need. To get an idea of how big a furnace you need first-hand, you can use our furnace sizing calculator here (just input square footage, and you will get a BTU estimate).

A properly sized furnace can last for at least 20 years.

2. Choose A Good Furnace Installer

How well a furnace will be installed will affect how long will a furnace last. In many cases, we see furnace installation just like any other installation; install it and be done with it.

However, we often see inadequate furnace installation. This is one of the most common reasons why furnaces do not reach their 15-year average lifespan.

What’s the difference between a good and bad furnace installation?

We can divide it into 3 parts:

  1. Good/bad ductwork. Ductwork is an extremely important part of furnace installation. Properly designed ductwork will allow for seamless airflow. Improper ductwork, on the other hand, will create pressure pockets. A furnace will have to work extra hard to for the airflow through these pressure pockets, adding unnecessary wear and tear, and decreasing the time how long do furnaces last. You can read a bit more about duct sizing here and look into the duct airflow velocity calculator here.
    ductworks affect how long do furnaces last
    Adequately sized ductworks are important in prolonging the lifespan of a furnace.
  2. Good/bad drainage system installation. This is only relevant for high-efficiency gas furnaces. They have a second heat exchanger that squeezes out an additional 10-15% of heat. A side effect of that is condensation, and that water has to be adequately channeled away from the furnace. As a result of bad furnace installation, you might see your furnace starting to leak water. This is not optimal and may damage your furnace, leading to a lower furnace life expectancy.
  3. Good/bad fuel lines installation. If you have a diesel or gas furnace, you will need fuel lines that supply diesel, oil, or gas to the furnace. We often see mistakes made in fuel lines installation which will, obviously, lead to the furnace breaking down sooner than expected.

A good installation may add up to 5 years to your furnace. Even more importantly, a bad installation (especially drainage system and fuel lines) is one of the most common reasons why a furnace might stop working after 5 or 10 years.

Solution: Here it makes sense to find a reputable HVAC company with experienced furnace installers and a good track record.

3. Regular Maintenance (Many Times Overlooked)

Regular maintenance goes without saying, right?

Well, while everybody knows that regular furnace maintenance is good for prolonging the furnace’s lifespan, not everybody actually invests in regularly scheduling HVAC-certified maintenance.

The main culprits that decrease the time furnaces last as a consequence of infrequent maintenance are:

  • Dirt buildup on the heat exchanger. If you don’t regularly clean the dirt buildup, it will start accumulating on your heat exchanger. If the heat exchanger, in turn, cannot transfer the heat as efficiently, the furnace will have to work harder to produce the required heating output. More wear and tear equals a lower lifespan.
    heat exchanger dirt buildup reduced furnace lifespan
    This is how a dirt buildup on a copper furnace heat exchanger looks like. You can imagine that the heat exchange here is not 100% efficient.
  • Dirty filters. Furnace filters have to be changed from time to time. You can check here about how often you should change air filters. Using dirty filters will restrict the airflow, again pushing the furnace to work harder to achieve the set temperature, adding wear and tear, and leading your furnace to an early grave.
  • Imbalanced fans. Fans can become imbalanced due to simple wear and tear, or dirt buildup. This can lead to fan motor failure which will again reduce the lifespan of a furnace.

You already know the solution here. It’s very important to schedule regular yearly furnace maintenance before every heating season (and sometimes after the heating season as well).

4. Lower Thermostat Setting (68°K Is Ideal)

Running any furnace at high operating outputs for prolonged periods of time can reduce the furnace’s lifespan dramatically.

A good way to reduce the load a furnace has to output is to lower the temperature setting on our thermostat.

Now, the ideal lower temperature would be 68°K in the winter. However, everybody needs to make a compromise between comfort and heating output.

If you can decrease the temperature on your thermostat for a degree or two, you’re actively working towards prolonging the years your furnace will function adequately.

4 Things That Decrease How Long Will A Furnace Last

Nobody really likes replacing a furnace every 10 years. Nonetheless, if you’re not a bit careful, you might end up having to prematurely throw the old furnace out and install a new one.

Here are the 4 things that can lead to a premature furnace failure:

  1. Inadequate sizing. As we have talked about earlier, too big or too small a furnace will unnecessarily add additional wear and tear, which can drastically reduce how long a furnace can last.
  2. Bad installation. The trio of bad ductwork, bad drainage, and bad fuel lines installation will severely impact the life expectancy of your furnace.
  3. No maintenance. Furnaces have to be regularly maintained to reach a 15-20 year expected lifespan. Dirty filters, dirt buildup on the heat exchanger and fans can negatively affect the health of your furnace.
  4. Higher thermostat setting. The higher the thermostat setting, the more wear and tear a furnace will have to suffer. Having a 75°K thermostat temperature in the winter, for example, will in most cases negatively impact the furnace’s longevity.


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