Where to find the serial number
Every furnace, air conditioner, heat pump and water heater has a data plate (rating label) with the model and serial numbers. Here's where to look.
Gas furnace
Turn off power at the furnace switch, then remove the front lower panel (the blower door). The label is usually on the inside of the cabinet or on the back of the panel. Some models also have a small serial sticker on the outside of the cabinet.
Air conditioner or heat pump (outdoor unit)
Look on the side or back of the outdoor unit, usually near the electrical connections or service valves. Labels fade in the sun, so a phone photo with the flash on often reads better than your eyes.
Tank water heater
The label is on the side of the tank, usually above the gas valve or the upper electrical access panel. It lists the model, serial, capacity and fuel type.
Tankless water heater
Check the side or bottom of the unit's cover. Some brands put it inside the front cover, so turn off power and gas before opening it.
Model vs. serial number
- The model number describes the product line, size and efficiency. Many identical units share it.
- The serial number is unique to your unit and usually encodes when it was built.
- Look-alike characters trip people up: O vs 0, I vs 1, S vs 5, B vs 8.