A combustion air regulating apparatus which is adapted for use with two stage induced draft furnaces and which allows such furnaces to be used with low cost AC inducer motors of the type having one or a small number of nominally fixed operating speeds. A flow restrictor assembly is disposed in fluidic...http://www.google.ca/patents/US5993195?utm_source=gb-gplus-sharePatent US5993195 - Combustion air regulating apparatus for use with induced draft furnaces
