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With the GSI-2 and Simple-Therm as your thermostat, you can control the AC via remote control, with schedules, and more!



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Master / Slave Operation. This master unit is mounted close to the air handler (furnace) unit. The wires coming out of the bottom are the standard thermostat connections (24 volts) and the power and temp probes. The master unit contains a relay board (GSI2-RLY) for connections to the HVAC system.



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The GSI-2 unit can be mounted in the living area and normally displays current inside/outside temperature. Turning the knob changes the set-point. Pressing the knob brings up the GSI-2 menu to turn the system to auto/heat/cool or fan.


PLEASE NOTE: The GSI-2 Controller has been discontinued. If your project calls for a similar controller, please contact Gunn Systems for more information.

Simple-Therm® Software

While many thermostats are available, few can match the capabilities of a GSI-2 unit running the Simple-Therm software.

Like Simple-Rulez, Simple-Therm files and source code are freely available.

Some rather unique features allow the GSI-2 unit to save energy beyond a simple set-back type thermostat.

This application is in continuing development and testing. Please contact us for more information.

  • One knob setting. Simply turn the knob to set the temperature. It doesn't get easier! 0.2 degree temp resolution to get it exactly where you want it.
  • IR Remote control. Uses a Standard TV remote (Set for Sony TV commands) to set temp and turn system on or off. You can change the thermostat from anywhere in the room!
  • Master-Slave operation. Remote-mounted units communicate through RS-232 Serial communications. Master is located near the HVAC unit, while the Slave can be mounted anywhere. Wireless operation is possible with optional RF modems.
  • Ambient (room lighting) Light Sensor compensates for day / nighttime (set back and save energy using a larger On-to-Off span).
  • Can drive Heat Pumps / Electric Heat / AC / Gas. Has emergency heat for heat pumps and has output for heat strip on heat pumps for large temperature differences.
  • Security code access option. With security code enabled, the user must first enter a combination (very similar to the way an old combination lock works) to gain access and set temperature or system on/off.
  • Handles degrees in Celsius or Fahrenheit.
  • Handles minimum compressor delay (programmable).
  • Handles minimum run time delay (programmable).
  • Programmable temperature calibration.
  • Programmable span (allowable temp span). Span may be programmed by time of day. Span may also be programmed via lighting and outside temperature.
  • Relays (two) on both master and slave can drive Damper Controls.
  • X10 interface emulates RCS (Residential Control Systems) Thermostat operation, allowing set-points and current temperatures to be sent over the house wiring to home automation system.
  • Zone level HVAC control in future version.

Simple-Therm requires the GSI-2 with the relay expansion board.


A Note about Applications for the GSI-2

These are just suggested applications. These are NOT complete products manufactured by Gunn Systems. All technology is offered with no warranty or assumed liability. USE AT YOUR OWN RISK.


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