A draft inducer blower assembly includes a blower having a fan, a dilution air intake passage, an exhaust gas intake passage, and a discharge passage. The blower is configured to operatively connect to a heater system in a manner to facilitate flow of combustion air into a combustion chamber and to draw dilution air into the blower and to mix the dilution air with the exhaust gases and to facilitate flow of the mixed air and exhaust gases through the vent. The dilution air intake passage is positionable in at least a low flow configuration and a high flow configuration. The dilution air intake passage is more restrictive of intake of dilution air in the low flow configuration than in the high flow configuration.