Description

Thermostat selection and wiring can greatly enhance the operation of a furnace retrofit. For example, a new furnace with a staged gas valve will not have access to all its features if a non-matching thermostat (single-stage) is selected. Furthermore, the number of connectors must also match between the furnace and thermostat if greater functionality is desired. thermostat / wiring incompatibilities may result in lower furnace efficiency and thermal comfort. Modern (two-stage or greater) thermostats can also be programmed to remind the user of the recommended filter replacement date(s).

Challenges

ECM MOTORS: In high-efficiency furnace replacements, the new furnace fan speed (CFM) and
existing ductwork are often not compatible. As a result, manufacturers have come up with system improvements that work with existing duct systems to improve comfort levels and reduce operating costs. Utilization of a staged gas valve with variable speed blower motors is the preferred choice for most installers and customers.

COMPATIBLE THERMOSTAT AND WIRING: In order to provide access to all of the features of the new furnace, a compatible thermostat with the same number of wires is required.

EXISTING CONDITIONS: Most existing thermostats have 2-wire LVT wiring, whereas most compatible
thermostats now require multiple wires.

Solutions

• Fish in new wiring with the appropriate number of wires and connect them in such away that it matches the operation of the staged gas valve.
• Where fishing in a new wire is too difficult, there are three solutions:
  • Find a new thermostat location where there is space for the appropriate number.
  • Locate the thermostat at / or near the furnace and use a remote sensor installed at the old thermostat location. This is an inexpensive option, however, every time a building occupant wants to view or change the settings, a trip down to the furnace is required.
  • Use a wireless thermostat. Note that wireless thermostats may be an additional expense and may require battery replacement as part of servicing.