Heat-exchange ventilation device

A heat-exchange ventilation device comprising:

• an air supply passage to guide external air from outdoor to indoor;
• an air exhaust passage to guide air from indoor to outdoor;
• an air supply fan to generate a supply air flow from outdoor toward indoor in the air supply passage;
• an air exhaust fan to generate an exhaust air flow from indoor toward outdoor in the air exhaust passage;
• a heat exchanger provided in a middle of the air supply passage and the air exhaust passage to perform heat exchange between the supply air flow and the exhaust air flow;
• a heater connection terminal to be connected with a heater that is installed in an outdoor air-supply duct connected on an outdoor side of the air supply passage and that heats the supply air flow flowing through the air supply passage into the heat exchanger;
• a temperature sensor to measure a temperature of the supply air flow passing through the air supply passage;
• and
• a controller to control operations of the air supply fan and the air exhaust fan and turning-on and turning-off of the heater based on a measurement result of the temperature sensor, wherein
• the air supply fan is operable at one of a plurality of intensities at which different air volumes of the supply air flow are generated, and
• the controller prohibits a state in which the air supply fan is operated at an intensity lower than an intensity set in advance and the heater is turned on.