An air heating and cooling system includes (1) a heat pump, illustratively devoid of auxiliary electric resistance type air heating structure, operative to provide refrigerant-based heating or cooling of air being delivered to a conditioned space, (2) a fuel-fired modular blower selectively operable to generate combustion heat, and (3) a control system associated with the heat pump and the modular blower. The control system has a heat pump thermostat electrically connected to a modular blower control and operative to transmit to the modular blower a first signal indicative of heating operation of the heat pump, and a second signal indicative of a need for alternative heat during a heating demand cycle. The modular blower is operative, in response to receiving both signals, to provide combustion-based air heating in place of refrigerant-based heat pump air heating.