How Long Should You Keep Your Furnace?

Your furnace is likely one of the most expensive appliances in your home. It can be expensive to repair or replace when there is an issue so people often scrutinize a furnace a lot when they are purchasing a home or having a new system installed.

One of the most common questions I get is, how long does a furnace last? In this article I’m going to explore that questions and help you get some practical advice for prolonging the life of your HVAC system.

How Long Does a Furnace Actually Last?

My favorite analogy to use when I answer this question is comparing your furnace to a classic car.

The fast answer to how long will a furnace last is, it can last as long as you want it to. What I mean by that is, there is not date at which a furnace needs to be replaced entirely.

Taking the classic car example, we still see cars on the road from time to time that were made 40, 50, 60, even 90 years ago right? Along the way, those cars needed repairs because no car (and especially older ones) was designed to last forever.

People simply fixed what was wrong with those cars to keep them driving on the road. Some of them probably needed way more repairs than others but the point is, someone wanted to keep that car running so they did.

The same is true for a furnace. It can last as long as you want to keep fixing it and there are really no scenarios (other than a catastrophic accident) where you have to replace your entire system. Typically when there is an issue with a furnace, it’s one part or one assembly of parts that has gone bad and needs replaced.

When is it good to get a new furnace?

There are two primary reasons that people replace their furnace systems.

1. It’s not safe to operate.
2. It’s not practical to repair your furnace (it’s no longer reliable, it’s too expensive, etc).

You can technically keep a furnace as long as you want however there are some scenarios where repairing it may not be practical. For example a cracked heat exchanger is a big issue because it causes carbon monoxide to leak out into your home. The furnace will still function as it should however that deadly gas will be leaking out.

In that case, it makes more sense to replace the unit because swapping out a heat exchanger may be more expensive. If the unit is older, new heat exchangers may not be available for it.

Any other time there is a safety issue or the furnace is just not repairable is a good time to replace the entire unit. Examples of this might be a fire in the home that has damaged the unit, a storm or other act of nature that has extensively damaged the unit, or an earth quake. Anything that has caused so much damage that it isn’t practical to repair the unit.

Your furnace may also be at an age where parts are continually breaking down making it unreliable. If you live in an area where it’s essential to have your furnace working and frequent service interruptions are dangerous, replacement may be a good idea.

What are the benefits of replacing my furnace?

Going back to our car analogy, there are benefits to getting a new car such as technological advancements. Older vehicles were made when we knew less about the air/fuel mixture in the engine, about aero dynamic design, and other fuel-saving measures.

The same is true for furnaces. An older furnace may not burn natural gas as efficiently as a newer model. Aside from any safety issues, if you have an older furnace and you find yourself repairing it a lot, a newer model may come with the added benefit of lower cost of operation.

You may also get to take advantage of more modern management add-ons like programmable or internet connected thermostats, more robust climate control settings, and quieter operation.

Final Thoughts

So that’s the truth about how long a furnace lasts. If you take care of it, do routine maintenance, and continue to fix it, you can theoretically make a furnace last a lifetime.

Of course, that may not always be the case and replacing your furnace has a ton of great benefits. The best course of action is to put safety as a priority for your heating system and then make financially-driven decisions after that.

Are Multi-Stage Furnaces Better Than Single Stage Furnaces?

A common misperception that customers have is that having a multi-stage furnace is what makes the furnace more efficient. Although it may at the margin, any benefits from a multi-stage furnace are not primarily related to fuel savings.

Comparing Furnace Models

  • The primary people who can benefit from multi-stage furnaces are customers who are trying to prevent temperature swings in their house.
  • An analogy would be: A single stage furnace is comparable to having a car that you can only floor the gas pedal or have it completely off. It gets you to where you want to go, but it will often overshoot the target, causing temperature swings and temperature fluctuations.
  • A single-stage furnace has been the predominant method of heating for the last half century and has worked well.
  • Some years back, they developed two-stage furnaces; the instant and most obvious benefit to a two-stage furnace is that the majority of the time, it runs at a much lower capacity while reserving the higher capacity for either when it gets colder or the furnace has been running for a longer period of time.


  • If a thermostat calls for heat and the furnace only fires up at 50% or 60% capacity, it more slowly brings the temperature up and is much less likely to overshoot the target. Because the fan has been running for a longer duration, it gives a better chance for the air to equalize in temperature throughout the house.
  • It’s important to note multi-stage does not just refer to fuel consumption, but a properly set up furnace will also adjust the fan speed to coincide with the adjustment in the fuel usage to keep the temperature rise relatively equal. (‘Temperature rise’ referring to differential in the air temperature entering the furnace and the air temperature leaving the furnace.)
  • Adjusting only the fuel and not the fan speed would cause the temperature in the furnace to be far too hot or too cold.

Variable Stage Furnaces

  • After multi-stage were invented, then came out variable stage with some models offering 60 stages and some models offering up to 100 stages with completely variable output up and down the spectrum.
  • This can sometimes lead to some negative consequences that were not anticipated well with manufacturers.
  • For instance: When furnaces modulate down too low and modulate the fan speed down too low, the fan size can be undersized for the size of the house in retrofit applications because the duct work system was not designed perfectly and the ducts are difficult to adjust as they’re buried in floors, walls and ceilings.


Our recommendation is to use two-stage furnaces for the vast majority of applications.

Top Tips to Consider When Buying A New Furnace

There are a variety of factors to consider when you are looking at purchasing a new furnace for your home.


One of the first things people consider when purchasing a furnace for their home is the brand. But this is actually one of the least important factors.

In our opinion, as long as you are dealing with one of the major brands, like Lennox, Carrier, Goodman, etc. – you are going to be fine! The key is, you just want the brand to be supported in the area. For instance, if the furnace were to break down in five or ten years’ time, you just need to have access to available parts, or more specifically, whatever company is repairing the furnace must be able to access the parts readily.

To think that some furnaces break down and some don’t is a bit of a stretch. The truth is, there’s probably a 10% variance between the best and the worst furnace in terms of likelihood of breakdown.

Noise level

Another factor people consider when purchasing a new furnace for their home is the noise level. This more specifically relates to the technology that you are installing vs. the brand of furnace. So, if you are looking for something quieter, you want to make sure you are putting in something high-efficiency, as it’s a different technology compared to what a mid-efficiency or low-efficiency is. High-efficiency takes all the potential sound and traps it in the furnace and sometimes transfers that sound outside.

Size of the new equipment being installed

Another factor that homeowner should not be worried about, but still you should be aware of – how the decisions are made – is the size of the new equipment being installed. You can’t rely on things online for the most part, because depending on the average winter temperature in your area, it will greatly impact what equipment gets installed. Sizing is based on the ‘winter design temperature’ for your area. Roughly meaning, what is the coldest it will ever get in your area? It needs to be able to heat at that temperature. So, the vast majority of the time, the maximum potential of the furnace is not needed and will never be used.

It is much more common for contractors to oversize a piece of equipment than to undersize it. And oversizing can lead to all sorts of negative effects, like prematurely wearing the furnace out, noise issues because the fan is too big and a variety of other factors.

One sub-category of the sizing issue is, there are two different things to size on the furnace: “the gas-sizing” and “the fan-sizing”. If you overdo the fan-sizing that will lead to problems, but if you underdo the fan-sizing, there won’t be enough air to push to the furthest parts of your home.

As a quick rule of thumb, I would suggest under-sizing on the gas, from what you think it is, and oversizing on the air flow. One of the best ways that we can do it is just to contact our sizing department and free of charge we will walk you through how we size the equipment.

Should Your Replace or Repair Your Furnace?

A really common thing that people wonder about is whether they should replace their furnace, or just repair it.

The most common time people contact a furnace company is when it breaks down. At this point, folks are faced with the decision of repairing it for x number of dollars or just getting rid of the thing. So, there are a few factors to consider if you’re making that decision.

The first and most obvious factor is age. As a furnace gets older it often loses efficiency, getting noisier, less safe, and definitely less reliable. So, as a general rule of thumb, furnaces beyond about 20 years old start to head downhill pretty fast. But if you are deciding whether it’s the right decision to replace your furnace, age does not always tell the whole story. Sometimes, 20 years ago, you (or whoever owned your home previously) put in an amazing, top of the line furnace that will last longer than 20 years.

Surprisingly, it also depends what area of the country you’re in. If you are in a southern climate, your furnace isn’t running very often, and you can probably keep it for much longer than those who live in a northern climate. The furnace of a homeowner in a northern climate will literally run 10 times more, and have much more wear and tear on it.

Another factor to consider is if you are planning on getting an air conditioning system in your home, and your furnace is older and doesn’t supply enough air. One thing you definitely don’t want to do is put in an undersized air conditioner or undersized heat pump just to accommodate your outdated and under-powered furnace.

Another factor to consider is how expensive the repair will be to get your furnace back online. $1000 repair costs for a less-than five year old furnace is probably worth it, since it will help your furnace last much longer. If you have a 10-year old furnace, and that repair is going to be $1000, you definitely do not want to dump that money into the repair.

As another general rule of thumb, all furnaces nowadays, for the most part, are high-efficiency. If your furnace is a mid-efficiency, meaning it does not have plastic venting and it is not a condensing furnace, it is likely better to put the money towards getting a new one, and take advantage of all the newest, latest-and-greatest technology. This is because sometimes, with lesser-available brands, you might not even be able to repair an older furnace. These are just a few things to consider if you’re thinking about repairing or replacing your furnace.

What To Know About Getting A New Furnace In The Seattle Area

So, you think you are ready to get a new furnace and you live in the Seattle area. What are the key factors you should consider when getting a new furnace? One of the most important factors to consider, which is not something that the homeowner should figure out themselves, is getting the right size of furnace.

The Size

The Pacific northwest, as a very rough rule of thumb, requires about 20 or 21 BTUs per square foot of home, but there are dozens of factors that can adjust the numbers significantly up or down like the age of the house, the insulation, having a crawlspace, the exposure of the house and many other things. So, the size of the furnaces going in there is very important. Also, important is that it’s completely not relative to the size of the previous furnace in the house. Oftentimes, furnaces in the house before back in the 60s, 70s, 80s or even 90s, were drastically oversized for the structure. Oversizing a furnace causes significant loss in efficiency, makes the furnace noisy and causes it to burn out prematurely.

The Brand

Another factor that people overestimate the importance of is the brand of the furnace. People sometimes are very specific to certain brands which, when looking at, breakdown statistics or other quality comparisons is not the most important factor. As long as you have one of the major brands installed at your house, you’re going to be fine as long as they have ready availability.

The Who

The next most important factor is who will actually be coming to your home to put the furnace in. You want to deal with a company that you can trust. In a company that you know if it breaks down 2 years from now, will readily be able to come back to your house to do the appropriate repairs.

The Cost

The next most important factor is cost. Nowadays, there are different ways to get a furnace into your house. Conventionally, going back to the old days the only option you had was to buy it. Nowadays, with the advent of subscription services for just about everything, you can now have a furnace installed in your house and just pay on a monthly basis and never pay anything for the furnace upfront.

In Addition

Factors that are generally not important in the Seattle area is having a humidifier because the humidity levels are relatively comfortable year-round. One thing that you may want to consider is adding a filtration system at the same time that you put in a new furnace. New furnaces have the ability to efficiently make the air circulate through your house 24 hours a day at low cost. So, if the air circulates anyway, you may as well filter the air 24 hours per day.

Regardless, give us a call at FurnaceUSA to get more information about getting a furnace installed.