Start with the equipment, not the thermostat
The thermostat identifies the control, not necessarily the heating or cooling equipment. Go to the outdoor condenser, furnace, air handler, heat pump, or packaged unit and look for the manufacturer rating plate.
The serial number is usually labeled “Serial,” “Serial No.,” “S/N,” or “MFG No.” The model number is a separate field. Photograph both lines together whenever possible.
Outdoor air conditioner or heat pump
Check the cabinet panel near the refrigerant service valves and electrical disconnect. On older equipment, the plate may be faded, painted over, or hidden behind a protective cover.
Do not remove a live electrical service panel just to read a label. A plate that is not visible from the exterior should be handled by a qualified technician.
- Right or rear cabinet panel
- Near service valves
- Inside the top lip on selected units
- Under a removable non-electrical information cover
Furnace or air handler
Turn off the system before opening a normal homeowner access door. The rating plate is often on the inside wall of the blower compartment or on the back of the removable door.
Avoid touching wiring, terminals, burners, capacitors, or sharp sheet-metal edges. If the label is behind a sealed or electrical compartment, stop and ask a technician.
Mini-split and packaged equipment
Mini-split indoor and outdoor units each have their own model and serial numbers. Record the outdoor unit first when you are checking system age, then capture the indoor heads if you need a complete equipment inventory.
Packaged rooftop or through-the-wall equipment often places the label behind a service door. Commercial access and rooftop work can create fall, electrical, and mechanical hazards; use a qualified professional.
Make the label readable
- Wipe dust with a dry cloth only
- Use side lighting to reveal stamped characters
- Take one full-label photo and one close-up
- Keep the camera square to the plate
- Double-check 0/O, 1/I, 5/S, 8/B, and 2/Z