Fan apparatus

A fan apparatus, comprising,

• a passage in which a fan is interposed;
• a switching device that switches an effective sectional area at a predetermined portion of the passage;
• and
• a control device,
• wherein:
• on a premise that at a state where the effective sectional area at the predetermined portion of the passage is switched to a predetermined first-area by the switching device, a value of a current flowing to the fan when a rotational speed of the fan is made to a predetermined rotational speed is defined as a first fan-current value, at a state where the effective sectional area of the predetermined portion of the passage is switched to a predetermined second-area which is larger than that of the first-area by the switching device, the value of the current flowing to the fan when the rotational speed of the fan is made to the predetermined rotational speed is defined as a second fan-current value, and a ratio of the first fan-current value to the second fan-current value is defined as a detected current ratio,
• the control device is configured to:
• memorize as a standard current ratio a detected current ratio that is detected when the fan apparatus is set up;
• and decide a clogging degree of the passage by comparison of a detected current ratio after detection of the standard current ratio with the standard current ratio.