What is furnace draft inducer or ventor motor?
The draft inducer is the small fan motor that set on the front of the furnace when you remove the outer panels, keep in mind not all furnaces have them.
Whenever the government mandated they had to raise efficiency on furnaces to a minimum of I believe of 80%, that surpassed what natural convection could do reliably. With the advent of the draft inducer they were able to control exactly how much air is moving through the heat exchanger. By doing so they could accuratley determine the amount of BTU'S and the AFUE. This is why it is so important when you change one inducer motor out that it is like for like and not a look alike.
It is true that the inducer clears the heat exchanger of any unburned gas, but that is not the true pupose of the prepurge mode. The 30-45 seconds the fan is running before ignition is doing a bunch of different things, but mostly the computer is checking limits, pressure switch, etc. to make sure system is ready to fire up. If in this time it finds an anomoly it will not allow furnace to fire up and you will get a code. The byproduct of this prepurge is that it gives you a shot of clean air for start up combustion, however this is not the prepurge primary goal.
Popular furnace motor brand are Fasco, Jakel Inc, Ametek Windjammer, Rottom, Broad Ocean.