How to Find Out How Old Your Furnace Is?

Whether you’ve recently moved into a new home with an existing furnace or are simply unsure about the system in your current home, it can be hard to know how to find out how old your furnace is.

A furnace will typically need to be replaced after anywhere from 15 to 20 years of service, so it’s important to know exactly when your furnace was installed.

There might be a tag or sticker that’s easily visible that tells you the make, model, serial number, and production date. But if you’re not so lucky, then there are still ways to find out the age of your heating system.

If you’re asking “how do I find out how old my furnace is,” this comprehensive guide aims to help you date your furnace accurately even if you’re missing the original documentation or receipts.

Key Takeaways

• The serial number is the key to determining furnace age. It’s usually located on a manufacturer’s label on the furnace exterior, inside the cabinet door, or stamped on components like the gas valve or blower.
• Most serial numbers encode the manufacturing date in the first four digits (either week/month + year, or year + week/month).
• Each brand has its own serial number format. You can check the manufacturer’s age chart or call them directly.
• Alternative methods to date your furnace: look for service tags showing installation or last service date; check warranty documentation for purchase or registration dates; ask an HVAC technician – they can often identify age by looking at the unit.
• Furnaces typically last 15 to 20 years. It’s time to replace your furnace if you’re experiencing frequent breakdowns, rising heating costs, uneven heating, strange noises, or repair costs approaching 50% of new furnace cost.
• Old furnaces have AFUE ratings around 60 to 70%, whereas modern Canadian furnaces must be at least 95% efficient.
• Older furnaces can also pose safety risks from cracked heat exchangers and carbon monoxide leaks.
• New furnaces feature electronic ignition, variable-speed fans, modulating valves, smart thermostats, and are much quieter.
• Replacement costs average $4,000 to $6,500, including installation.

What’s New for 2026

When it’s time to buy a new furnace, the biggest change for 2026 is that furnaces are incorporating AI and machine learning to adjust heating based on routines, occupancy, and weather, as well as to provide predictive maintenance alerts.

A Key to Determining Furnace Age: The Serial Number

Find the Serial Number

When trying to answer “how old is my furnace,” start by locating the unit’s serial number.

However, finding this sometimes isn’t immediately obvious. Depending on the specific manufacturer as well as the year of production, the serial number might be found in a number of different locations.

Look for the manufacturer’s label. This will be a paper or metal tag, sticker, or imprint. Newer models will often have the information somewhere along the outside surface of the furnace. However, if it’s not there, open the cabinet door to see if there’s anything posted inside.

Older models may require a bit more digging. Shut off the power to your furnace and take a look around inside the unit. The serial number could be stamped into one of the components. Common places to find the serial number include the:

• Gas valve
• Fan or fan blades
• On the inside of the access panel
• On the blower compartment panel
• The interior cabinet

Using the Serial Number to Date Your Furnace

Once you’ve located the serial number, you’ll probably have to investigate to figure out the exact details of your furnace. This is because the serial code rarely states the actual production date clearly.

There are a few ways to do this. Some are easier than others, but we’ll go over all the tricks to help you figure out the age of your furnace.

Method One: Check with the Manufacturer

The easiest way to find out how old your furnace is using the serial number is to check with the manufacturer. In the case that you know the brand, simply use the brand’s furnace age chart to identify your own model.

Alternatively, call the manufacturer to ask them how to tell how old your furnace is based on the information you have.

A manufacturer representative may be able to approximate the age of your furnace by looking at a photo of the unit, even without a serial code.

Method Two: Deciphering the Serial Number

When you don’t know what brand your furnace is, can’t find an age chart, or can’t get in touch with the manufacturer, you can still use the serial number to date the unit.

The orientation and combination of the numbers and letters will differ depending on the make and year, but most serial numbers contain the week or month and year of production. Let’s talk about some of the most common serial number styles:

• Week/month and year as the first four digits: It’s usually the first four digits of the serial code that indicate the manufacturing week/month, followed by the year. So, in the case that you see 2-3-9-8 followed by more digits or letters, for example, it likely means that the furnace was produced in the 23rd week of 1998.
• Year and week/month as the first four digits: Alternatively, the year might come first and the week/month second. In that case, the first four digits of the serial number might look like this: 0-2-1-2, for 2002, December, or 2002, the twelfth week.
• Date at the end: Sometimes, but not often, it’s the last four digits of the serial number that indicate the model’s production date.
• Letters indicating months or years: Another variation you might see is using a single letter to represent a month or year. For example, a serial number might read 02B, where 02 is the year (2002) and B means February. When letters represent months, the code usually starts with January being A, February being B, etc. However, sometimes January will start at M, February N, etc.
• Serial number with a letter at the beginning: When a serial number starts with a letter, this often represents something like the factory or location, and the date of production usually follows.

Tips about serial numbers:

Some manufacturers skip the letter I (and sometimes J as well) to avoid confusion with the number 1, so September might be represented by J or K.

If the serial code reads 0-7-3-4, it’s easy to tell that it was made in the 34th week of 2007, as it isn’t likely to be from 1934.

How to Tell How Old Your Furnace Is: Analyzing Serial Number Examples from Actual Manufacturers

Other Ways to Tell How Old a Furnace Is

Look for Service Tags

You can also find out how old your furnace is by looking for a sticker or tag indicating the date when your furnace was last serviced. This tag may list the date that the furnace was installed. Although this isn’t the same as the production date, it can give you a decent estimate of the unit’s age.

How to Tell How Old My Furnace Is Using Warranty Information

All furnaces in Canada come with at least a basic warranty, and if you still have the warranty documentation, then you might be able to find out how old your furnace is.

The document may have a purchase date or warranty expiration date, and from there you can work backward to calculate when the warranty started and how old the furnace is.

Further, if the warranty was registered, then the manufacturer will have a record of the registration date, which can give you a pretty good idea of the furnace’s age.

Ask an HVAC Specialist: How Do I Know How Old My Furnace Is?

Experienced HVAC technicians will have many years under their belts, and that likely means they’ve seen it all. These experts might be able to identify your furnace just by looking at it, even if the brand and serial number aren’t obvious.

Moreover, they might see other clues to help you date the unit, and will be able to recommend options for maintenance or upgrading.

How Old Is Too Old for a Furnace?

Furnaces generally have a lifespan of 15 to 20 years. While it’s not unheard of for a well-maintained system to last 30 years, if yours is around 20 years old, it’s probably getting close to the end of its lifespan.

Here are some signs your furnace is getting too old:

• Frequent breakdowns/repairs
• Rising heating costs not associated with energy prices
• Uneven heating
• Strange noises
• Repair costs are around 50% of the cost of a new furnace

Talk to an HVAC pro and have your furnace inspected. Older furnaces can pose a safety risk because of cracked heat exchangers and carbon monoxide leaks.

What’s more, your furnace could have an AFUE as low as 60% depending on its age, which means you could save a lot on heating bills by upgrading to a high-efficiency model.

How Do Old Furnaces Work?

When it comes down to basics, old furnaces work very much the way modern ones do. The differences come when you look at new technologies/design features that old furnaces won’t have, and these might be able to help you find out how old your furnace is roughly.

Here are some key comparisons between older and newer furnaces:

Burner: An older furnace will likely have an actual burner and a pilot light instead of an electronic or direct spark ignition.

Heat exchanger and blower: Old furnaces will still have heat exchangers and blowers, but they’ll be less efficient compared to newer designs. Old blowers will likely be noisier as well.

Operation: Most furnaces that are older than 20 years will probably only have single-stage operation. That means they have ON and OFF settings, but nothing in between. Many newer furnaces feature two-stage or modulating burners that produce more consistent heat more efficiently.

Draft: Older furnaces used gravity to move air through the system. These are known as natural draft furnaces. Modern furnaces use a fan or blower to force air through the system.

Common Problems with Old Furnaces

Older furnaces can act up from time to time because they’re not built with the same efficiency or durability as newer furnaces. Sometimes, simple wear-and-tear on your furnace is enough to cause issues that are difficult to take care of.

Here’s a list of common problems:

Pilot Light Troubles

Most modern furnaces have a Hot Surface Ignition, similar to the filament in a lightbulb. Older furnaces use a flame that is kept going by a constant small amount of gas. This doesn’t tend to be very efficient, and can cause trouble by creating carbon monoxide.

Damaged ignition, drafts or debris can also hinder the pilot light from working, and will likely need repair or replacement.

Blower Problems

This can be a simple or complicated problem to solve in an aged furnace, but essentially it means that heat and air are not getting to where they need to be. Sometimes the belt just needs to be lubricated, other times it may need to be replaced. If the blower itself is running constantly, it indicates a need for repair.

Chronic Cycling

Older furnaces can start catching bad habits from neglect. One such action is the furnace turning on and off quickly, or going through its cycles constantly. It could be something like a dirty air filter or a malfunctioning sensor.

Noisy Furnace

Modern furnaces typically have more insulation and will be in better condition than an older furnace. When your furnace starts to make odd sounds, it could likely be any issue. Starting with the sound will help you pinpoint what’s going on. Rattling, squeaking or rumbling mean different things, which could indicate loose panels, a slipped belt, or old bearings; or possibly something else.

Malfunctioning Thermostat

This may have nothing to do with the furnace itself and may simply require new batteries or attention. If it’s an older thermostat, there’s the possibility that it has become defective.

How Much Does It Cost to Replace an Old Furnace?

The average cost of a new furnace in Canada is between $4,000 and $6,500, and that includes installation. However, when you’re replacing an older furnace, there are factors that can impact the cost, such as:

• Upgrading ductwork
• Size of your home/furnace
• Furnace efficiency/make/model
• Installation complications
• Where you live

While a new furnace is an investment, upgrading to a high-efficiency heating system can reduce energy costs and improve indoor comfort.

Benefits of New High-Efficiency Furnaces

Modern furnaces are a lot more efficient than the older ones, partly due to new technology and partly due to the basic standards that they’re required to meet.

The AFUE rating shows how much fuel is actually going into heating your home, so a rating of 90% means that 90% of your gas is used as intended with only 10% wasted. Modern furnaces sold in Canada need to have an AFUE of at least 95% and most are much higher (up to 99%), while older furnaces are lucky to be close to 70%.

Beyond the higher efficiency ratings, new furnaces are also advantageous because they have more sophisticated design features and technologies, including:

Electronic Ignition

One of the eco-friendly and cost-saving features in a new furnace is the electronic ignition, which has replaced the pilot light. Electronic ignition creates a spark as needed and doesn’t waste fuel running a pilot light that is constantly on, whether it’s needed or not.

Airflow

Airflow is typically induced and controlled so that every part functions regularly and efficiently. An ECM or Electrically Commutated Motor will provide precise control of airflow, resulting in a quieter furnace with a more efficient operation.

Fans and Valves

Variable-speed fans and modulating valves help heat your home with precision and stop the on-off cycle that is common in older furnaces. This means that you use exactly the amount of energy needed and no more to heat your home, and it increases longevity from less tedious cycling.

Reduced Noise

You’ll also notice less noise from the droning and rattling of an old furnace. Modern furnaces are sound-insulated, and also have parts that are seamless and won’t clang. In addition, the variable-speed fans operate quietly since they don’t need to run at full speed or stop, which is often a cause of a noisy furnace.

Thermostats

Smart thermostats can help regulate throughout the seasons, so you won’t have to worry about getting stuck on one setting and forgetting. They have a lot of features beyond just temperature.

Some thermostats can send text messages and other alerts about maintenance and issues that arise. When paired with a humidifier, they can help create a comfortable atmosphere in your home, year-round.

Talk to an HVAC Expert for Professional Advice

Once you’ve determined that your old furnace needs replacing, it’s a good idea to call an HVAC professional to get a suggestion and estimate for what your home needs.

Heating a home adequately and eliminating cold spots is about choosing the right features, sizing the furnace properly, and managing airflow.

Our guides can give you a place to start in your furnace education and help you make an informed choice.

For professional service, get a free no-obligation quote from a certified local HVAC contractor.

FAQ

Where can I find my furnace information?

When you’re looking for the serial number or manufacturer’s label to find out how old your furnace is, check for a nameplate on the side or front of the unit or on the inside of the access panel door. If you can’t find a label, you might still find a serial number on a gas valve, fan blade, blower compartment, or other component.

Is a 20-year-old furnace old?

Yes, a 20-year-old furnace is at the end of its lifespan. Even though you might still be able to get a few more heating seasons out of it, it’s probably worth replacing if your heating bills are going up, the furnace is heating unevenly, you’re facing expensive repairs, or you could get a better and more efficient unit by upgrading.

Can you tell the age of a furnace by serial number?

You can often find out how old your furnace is by the serial number, but each manufacturer has a unique format. Learn more about what serial numbers mean.

Resources

• Building Intelligence Center (serial numbers)
• How to Determine the Age of a Furnace
• Is a High-Efficiency Furnace Right for Me?
• How to Determine the Age of a Furnace