Controller for two-stage heat source usable with single and two stage thermostats

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 heating from the single-stage thermostat connected to the first terminal, or for connection to the two-stage thermostat for receiving a signal requesting low-stage heating from the two-stage thermostat connected to the first terminal;
• a second terminal for receiving a signal requesting high-stage heat operation from the two-stage thermostat connected to the second terminal;
• a microcontroller in communication with the first and second terminals, the microcontroller being configured to determine a duty cycle value for one or more heating cycles based on the duration of time in which the heat signal at the first terminal is present relative to the duration of the heating cycle, and to select a low stage time limit from a number of low stage time limits corresponding to a number of duty cycle values from a look-up table in a memory of the microcontroller, wherein the microcontroller is configured to control the operation of the two stage heat source to provide low stage the low stage heating operation when the heat signal is present at the first terminal up to the low stage time limit determined from the duty cycle valve, and to provide the high stage heating operation while the heat signal is present at the first terminal beyond the low stage time limit;
• and
• wherein the microcontroller controls the operation of the two stage heat source to provide the second stage heating whenever the heat signal requesting the second stage heat operation is present at the second terminal.

A method for controlling the operation of a two stage furnace comprising:

• determining whether a request signal for heat operation is present at a first terminal;
• calculating at least one duty cycle value based on a duration of time in which the request signal was present at the first terminal in a previous heating cycle relative to the total duration of the previous heating cycle;
• determining a low stage time limit value from the at least one calculated duty cycle value;
• providing for low stage low-heating operation as long as a signal is present at the first terminal until the low stage time limit is reached;
• providing for high stage high-heating operation after the low stage time limit has been reached, as long as the signal at the first terminal remains present;
• and
• discontinuing all heating operation when the signal at the first terminal is no longer present.

A method for controlling the operation of a two-stage heating system, the method comprising the steps of:

• actuating low stage heating operation upon detecting a request signal for heat operation at a first terminal;
• calculating at least one duty cycle value based on a duration of time in which the request signal was present at the first terminal in a previous heating cycle relative to the total duration of the previous heating cycle;
• determining a low stage time limit value from the at least one calculated duty cycle value;
• initiating a low stage timer means that is set to the low stage time limit;
• continuing the low stage low-heating operation as long as a signal is present at the first terminal until the low stage time limit expires;
• activating high stage high-heating operation after the timer has expired;
• continuing the high stage high-heating operation as long as a signal is present at the first terminal after the expiration of the timer;
• and
• discontinuing all heating operation when the signal at the first terminal is no longer present.