What a smart thermostat saves, and what it does not
A thermostat controls when the system runs. That is a real saving and a firm limit, and the wiring decides whether it can be fitted at all.
4 min readUpdated
A smart thermostat is a scheduler with a good screen. Everything it saves comes from running the system less at times you did not need it, which is genuinely worth having and is also the whole of the effect.
Where the saving actually comes from
- Setbacks that hold reliably, rather than a schedule nobody kept.
- Not conditioning an empty house, through geofencing or occupancy sensing.
- Runtime reporting, which is the first honest picture most homeowners get of how long their system is on.
- Filter reminders based on hours run instead of a date on the calendar.
What it cannot do
It will not fix a room that is always wrong, because that is a distribution problem and a thermostat measures one location. It will not make an oversized system dehumidify. It will not improve efficiency while the system runs, because it has no influence over the equipment beyond telling it to start and stop.
Check the C wire before buying
Most smart thermostats need a common wire for continuous power. Older homes frequently do not have one run to the thermostat location. The fixes are a pulled wire or an adapter at the air handler, both straightforward, but both worth knowing about before the box is opened. Multi stage, heat pump and zoned systems also have wiring requirements a general purpose model may not meet.