Line voltage thermostats are installed in a series with a single stage conditioning system on a 120V or 240V line. Electricity flows through the thermostat to the system allowing the thermostat to complete or break the circuit based on room temperature. Typically they control a zonal heating system, but can occasionally control a central electric furnace. This measure specifies two thermostat types Electronic Line Voltage Thermostats (ELVTs) and Line Voltage Communicating Thermostats (LVCTs).
There are a few ways ELVTs and LVCTs could save energy. All ELVTs may reduce deadband and reduce drop while some offer programmability. LCVTs could save energy through connectivity and on-board occupancy sensors or geofencing, though the later is not incorporated into into proposed savings estimate due to lack of data.
The saving mechanisms have not been confirmed. For this reason, and given lack of studies showing conclusive energy savings (most studies are inconclusive, with some even showing negative savings), the measure is set to "Planning" category, with a research strategy.
At the measure's most recent review, the RTF set the measure savings to zero. This is the RTF's best estimate of savings, which is based on a reconsideration of the merits of the savings mechanism in light of the many decades of study, which have not yet confirmed the savings mechanism nor shown reliable savings estimates. In addition to zeroeing-out the savings estimtes, the RTF also set the measure to "Under Review" status for a three-year period. This will allow time for an ongoing impact evaluation to be completed and to be considered by the RTF at the measure's next update.
