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Where is the serial number?
Every furnace, air conditioner, heat pump and water heater has a data plate (also called a rating plate or nameplate) with a model number and a serial number. The serial number is the one that holds the date.
On a furnace
Take off the front lower panel (turn the power off first). The data plate is a metal or foil sticker on the inside of the door or on the side of the cabinet, next to the blower. The serial number is usually labelled "Serial No.", "S/N" or "Ser. No."
On a air conditioner
On the outdoor unit (the condenser), look for the data plate on the side panel, often near the electrical box where the power cables go in. The indoor coil or air handler has its own plate with a different serial number.
On a heat pump
On the outdoor unit, look for the data plate on a side panel, usually near the electrical box. Heat pumps and air conditioners look alike; the model number or the plate will say "heat pump".
On a water heater
The rating plate is a sticker on the side of the tank, usually at eye level or just above the gas valve or the upper access panel. Many water heater labels also print the manufacture date, so check for that first.
On a tankless water heater
The rating label is on the side or bottom of the unit, or inside the front cover. Some models also show the serial number in the unit's service menu.
Model number or serial number?
- The model number is shared by every unit of that product. It usually describes capacity and features, for example a string ending in 060 or 036.
- The serial number is unique to your unit. It is usually labelled "Serial No.", "S/N", "Ser. No." or "N° de série".
- If the plate has a printed "Mfg. date" or "Date of manufacture", that's the answer, and you don't need to decode anything.
- Can't read it? Take a photo with flash from an angle, then zoom in. Faded foil labels are often easier to read in the photo.