Described herein is an apparatus and method for avoiding frost buildup on the air intake and or ice buildup on the ice condensing surfaces of the exhaust vent of a condensing appliance. The apparatus comprises a heat-conducting path that extends between the exhaust gas in the exhaust vent of the appliance, and the frost condensing surfaces at or near the air intake opening of the combustion air vent. The heat-conducting path has a first section in thermal contact with the exhaust gas and a second section in thermal contact with the frost condensing surfaces at or near the air intake. In one configuration, the heat-conducting path is a heat pipe. In one configuration the heat-conducting path is a heat exchanger assembly. The passive transfer of heat energy via the heat-conducting path, from the exhaust gas to the frost condensing surfaces at or near the air intake, avoids frost buildup.

The present disclosure addresses systems, media, and methods of configuring a heating system comprising a plurality of combustion-type heating devices fluidly coupled to a vent system. Configuring the heating system includes receiving operating pressure data from one or more pressure sensors in a flue of one of combustion-type heating devices and the vent system. The operating pressure data from the one or more pressure sensors is indicative of a pressure at a corresponding location in the vent system. Configuring the heating system further includes comparing the operating pressure data to stored operational pressure data indicative of operational pressure ranges indicative of permissible operating parameters associated with preventing backflow of flue gases into the one of combustion-type heating devices and outputting instructions for a damper to at least partially open or at least partially close based at least in part on the operating pressure data and the stored operational pressure data.

This disclosure relates generally to a system to dehumidify, alternately heat or cool a first space, and/or provide a controlled amount of CO.sub.2 to the first space. The system includes an indoor unit with a gas furnace with a first coil, and a second indoor coil. The first indoor coil and the second indoor coil are in fluid communication. A damper is in fluid communication with the exhaust for the gas furnace, for directing an amount of CO.sub.2 from the gas furnace to the first space. A control module is in electrical communication with the first indoor unit and the receptacle to control a position of the damper between an open position and a closed position, wherein the open position of the damper allows the amount of CO.sub.2 to be provided to the first space.