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 a difficult process trying to determine exactly 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.

This comprehensive guide aims to help you date your furnace accurately even if you’re missing the original documentation or receipts.

A Key to Determining Furnace Age: The Serial Number

Find the Serial Number

When trying to determine the age of your furnace, the first item you’ll have to locate is 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.

Typically, you’ll be looking for either 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 use a 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 about the production date of your furnace, assuming they’re still in business. 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.

Analyzing Serial Number Examples from Actual Manufacturers

Other Ways to Determine the Age of Your Furnace

Look for Service Tags

Another trick to identifying the age of your furnace is to look 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.

Ask an HVAC Specialist

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.

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.

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 90% 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.

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