A blower systems includes a blower housing, a gasket, and a clamp. The blower housing includes a dilution air inlet port having a tubular portion with an end margin having a plurality of flanges separated by slits enabling flexing of the plurality of flanges to resiliently move radially inwardly from an unflexed position. The gasket extends within the end margin of the dilution air inlet port. The air supply system includes an inlet portion, a combustion air portion, and a one-piece fitting having an inlet, dilution air outlet, and a combustion air outlet. The clamp is positioned radially about the plurality of flanges such that it can secure a source of dilution air within the dilution air inlet port.