I want to install a Honeywell RTH8580WF Wi-Fi thermostat in place of an existing Honeywell thermostat, but there is no C wire connected to the existing thermostat (which may explain why we have to keep replacing batteries in it) and no "Spare" wire that could be connected to C at the HVAC unit and at the thermostat -- even if I could get at the furnace: these are rented premises.
I've read that it's possible to use an external 24V transformer, but Honyewell tech support just told me in a chat that that's possible only for 2-wire heat-only systems.; is that true? There are posts and YouTube videos that seem to suggest otherwise. This is a 4-wire gas and A/C system.
Advice?
Perce