Programmable thermostats for forced air and hydronic systems, in 5-1-1, 5-2 and 7-day schedules, from single-stage up to 3 heat / 2 cool.
The setback is where the savings come from, and it works differently on different equipment. A furnace recovers quickly, so a deep overnight setback pays. A heat pump does not — a large setback forces the auxiliary resistance heat to make up the difference on recovery, which costs more than the setback saved. Heat pump installations need a thermostat with adaptive or intelligent recovery, and a shallow setback.
Stage count has to match the equipment. A two-stage furnace on a single-stage thermostat runs on high fire only and loses both the efficiency and the comfort the second stage was bought for. Check the terminal designations against the appliance wiring, not against the old thermostat — the old one may itself have been wrong.
C-wire is the practical obstacle on retrofit. Many older installations have no common wire, and a thermostat that needs continuous power will short-cycle or fail without one.
Brands include Resideo, tekmar and DiversiTech.
