Upon detection of a flammable gas condition, an intelligent thermostat regulates operation of appliances that have sources of ignition which could be the source of or may ignite the flammable gas. This hazardous condition is detected by a flammable gas detector and is communicated to the intelligent thermostat by wired or wireless communications. The intelligent thermostat then communicates with these appliances either via wired or wireless communications. The intelligent thermostat may also provide a visual warning user interface screen to inform the occupant of the hazardous condition, and may signal smoke detectors in the dwelling to sound an audible flammable gas warning. Alternatively, the flammable gas detector may signal the smoke detectors in the dwelling to sound an audible flammable gas warning directly.