Yes, you need Smart Maintenance hardware on every HVAC system that you want to monitor. If you have more than one heating and cooling system in your home, you’ll need Smart Maintenance hardware (sensors) on both sets of equipment if you want to monitor both of them. We consider an HVAC system to be a heater/furnace/air handler/indoor unit AND a heat pump/air conditioner / outdoor unit. If you have multiple systems, you have the option to install the smart technology on one or more systems.