Do You Have The Furnace Code? How to Read the Code of Your Furnace!

If you own a home with a forced-air furnace, you know that fall and winter are the seasons for using it. But what do you do if something goes wrong and your furnace has to be repaired or replaced? How can you make sure that any company or technician coming into your home to service the unit knows exactly what they’re dealing with? And how can you ensure that your new furnace is installed properly and meets current codes? Fortunately, every forced-air furnace is fitted with a code tag that lists all relevant information about the system. This article will explain what each character on this tag means, which pieces of information are important, and why it’s so crucial to have this document available in case of emergency repair or installation.

What is a Furnace Code Tag?

A furnace code tag is a metal tag attached to the furnace with information about the system’s make, model, serial number, and other details related to the installation, wiring, and operation of the unit. This code tag is legally required on all forced-air furnaces, hot water boilers, and natural gas and propane water heaters. The purpose of this tag is to provide important information about the system so that technicians can understand the installation, know what to expect inside the ductwork, and be aware of any special codes and standards the unit was installed to meet. This information can be used to troubleshoot problems, diagnose issues, and ensure that repairs follow code and are safe and effective. If your furnace breaks down and needs to be replaced, the new technician can also use this information to know exactly how the old unit was installed and where to install the new one. This can help save time and money because they can avoid common installation pitfalls.

Finding the Furnace Code Tag

The best place to look for the furnace code tag is on the outside of the furnace unit. It might be on the front of the unit is installed in the front of the house, or it might be on the side or back of the furnace if it’s installed in an out-of-the-way location like a garage. The furnace code tag on your furnace might be covered with dirt and grime, or it might be completely rusted over. If you can’t read it or it’s completely illegible, take a picture and then clean or replace the tag as soon as possible.

The Meaning of Each Character

The first character on the furnace code tag tells you the type of fuel used to power the unit: – n for natural gas – o for oil – g for propane – h for hot water The second character tells you the system’s BTU rating: – 0 for a 0-15,000 BTU system – 1 for a 16,000-29,000 BTU system – 2 for a 30,000-39,000 BTU system – 3 for a 40,000-49,000 BTU system – 4 for a 50,000-59,000 BTU system – 5 for a 60,000-69,000 BTU system – 6 for a 70,000-79,000 BTU system – 7 for a 80,000-89,000 BTU system – 8 for a 90,000-99,000 BTU system – 9 for a 100,000+ BTU system

Important Info in the Code Tag

– The System’s Make and Model: This information helps the technician understand exactly what system you have installed and can help them find parts if they’re needed. – The System’s Serial Number: This number can be used to determine when the furnace was installed. This can be helpful if the system needs to be replaced and the homeowner wants to make sure that the new one is the same size and can fit in the same ductwork. – The System’s Installation Details: This information is helpful for a new technician who is putting in a new furnace and needs to know if there are any special considerations based on the original installation. For example, if the old furnace was installed in a crawlspace, the technician will want to avoid putting the new furnace under a similar situation because it can lead to damage and water damage. – The System’s Vent Location: This information is crucial for a new technician who is installing a new furnace because the correct vent location is crucial for proper operation and safety. Even a small deviation from the old installation instructions can result in dangerous operations and multiple safety hazards.

Codes & Standards a Furnace Should Meet

A furnace that’s installed properly and meets current codes will be safe, durable, and energy-efficient. The heater and ductwork should be properly sealed and soundly constructed to avoid fires and other safety hazards. A new furnace should also have an airtight and watertight duct system that is properly sized to meet the home’s current needs. If you’re purchasing a new furnace or having an old one replaced, make sure that it meets the latest codes and standards. Codes change frequently, so it’s important to make sure that any technician installing a new furnace meets these standards. This will ensure that your new furnace is installed properly and is safe and durable for years to come.


A furnace code tag is an important tool for homeowners and technicians alike. If a furnace needs to be repaired or replaced, this tag can help technicians understand exactly what they’re dealing with, what to expect inside the ductwork, and if there are any special considerations based on the original installation. Even if everything is working properly, the code tag is still important because it shows technicians which parts were used for installation and can help them rule out potential problems before they start. A furnace code tag can help keep you and your family safe, no matter what season it is.