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Choosing the Right Thermostat
 

Purpose:

The purpose of this documentation is to provide customers with the proper knowledge to choose the proper thermostat (tstat) for the desired application. Although Leviton tstats are classified as electronic, communicating models, they are considered typical “mechanical” models, with regards to functionality. Also, there are some additional factors that can affect which product is used.

Discussion:

Proper tstat selection will typically depend on three (3) primary factors:

  1. Conventional Heat/Cool or Heat Pump
  2. Single vs. Multi-Stage
  3. Zone/Damper Control

HAI manufactures 2 primary models of tstats – RC-1000 and RC-2000. They are applied as follows:

  1. RC-1000 – This model is used for single stage conventional heat and/or cool systems, as well as single stage heat pump systems (Single stage cool and primary heat, with auxiliary heat support). Although designed to support “power-stealing” (employing R, G, Y, and W), HAI recommends using a common in all applications. NOTES:   In heat only applications, three conductors (R, W, and C) are required. A cool only application requires four conductors (R, G, Y, and C). The RC-1000 can be used in many (not all) zone control applications that “do not” require a master/slave or similar configurations.
  2. RC-2000 – This model is designed for use in multi-stage conventional heat/cool and heat pump systems, providing up to two stages of cooling and up to three stages of heating. The RC-200 can also be used in single stage systems. This model “is required” for applications employing Master/Slave zoning applications. The RC-2000 also has a built-in humidity sensor and output control for humidity applications.

Additionally, the following models, which have been discontinued, would be applied as follows:

  1. RC-80B – This model is used for single stage conventional heat and/or cool systems - it was originally designed as a “power-stealing” tstat (employing R, G, Y, and W), but with the addition of the back light feature, most applications require a fifth conductor for the common. NOTE:   In heat only applications, three conductors (R, W, and C) are required. A cool only application requires four conductors (R, G, Y, and C).
  2. RC-90B – This model is used primarily in zone/damper applications where a master/slave configuration is employed. It can also be used in applications to replace the RC-80B, where the “power-stealing” feature is causing performance issues.
  3. RC-100B – This model is used for single stage heat pump systems and has an auxiliary heat feature. This model is not designed for “dual-source” heat pumps, although in some applications, there is an Emergency Heat work-a-round available.
  4. RC-112B – This model is used for multi-stage heat pumps. It provides two stages of cooling and up to three stages of heat.
  5. RC-122B – This model is used for multi-stage conventional heat/cool systems and provides 2 stages of cooling and heating.

Zone/Damper control products can introduce some interesting dynamics in tstat selection. Some of the more important dynamics are:

  1. Older control products utilize a master/slave configuration, which would require the use of an RC-2000 at the Master, as well as each Slave location.
  2. Transformers – In some applications, the zone/damper controller will only provide 24VAC for the master tstat. In these applications, a 24VAC, 5-20vA transformer can be connected to the Rh and C terminals of the RC-2000 in Slave locations (CRITICAL NOTE: the factory jumper between Rc and Rh must be removed in this application).
  3. Some zone/damper control companies have begun manufacturing products that utilize tstats designed to “communicate” directly with the zone/damper controller. Some examples are the Carrier Comfort zone and Infinity Control, the Trane Comfort Link, and the Bryant Evolution. In these applications, Leviton tstats are 100% incompatible and cannot be used without additional hardware (Leviton automation controller and zone control RS-232 interface).
Article ID: 1053