The boiler blowdown rate is the quantity of water removed from the boiler for the purpose of controlling water parameters by periodic blowdown. Typically this value is expressed as a percentage of the feedwater input to the boiler. 5% is the normally specified value for blowdown rate but highly depends on the boiler feedwater quality. Blowdown rate can be calculated as: qBD = qS fc / (bc - fc) Where: qBD = blowdown rate (lb/hr) qS = steam consumption (lb/hr) fc = Total Dissolved Solids (TDS) in the feed water (ppm) bc = maximum allowable TDS in the boiler water (ppm)