Patent ID: 7731096

Claim:
A controller for a two-stage heat source, adapted to be connected to either a single stage or two-stage thermostat, the controller comprising: a first terminal configured for connection to the single-stage thermostat for receiving a signal requesting heat operation from the single-stage thermostat connected to the first terminal, or for connection to the two-stage thermostat for receiving a signal for first-stage heat from the two-stage thermostat connected to the first terminal; a microcontroller in communication with the first terminal, the microcontroller being configured to calculate a duty cycle value based on a duration of time in which a heat signal is present at the first terminal relative to a duration of a heating cycle, and to determine a first stage time limit that is determined from the duty cycle, wherein the microcontroller is configured to control the operation of the two stage heat source to provide first stage low heating operation while the first stage heat signal is present up to the first stage time limit, and to provide second stage heating when the first stage heat signal is present beyond the first stage time limit period.