Check the outdoor unit for a label that says “heat pump”
Look for a reversing valve on the outdoor unit
See if the system can provide both heating and cooling
Check whether the thermostat has an “emergency heat” or “aux heat” setting
Look for warm air coming from the vents in winter without a separate furnace running
Inspect the indoor air handler for electric heat strips
Check if the outdoor unit runs during heating mode
Review the equipment model number online
Look at the owner’s manual or installation paperwork
Ask an HVAC technician to identify the system