Noncondensible gases in the condenser will reduce the energy efficiency of centrifugal water chillers. Noncondensible gases were injected into the condenser of a 250-Ton R-11 centrifugal chiller, and measurements were taken to determine their effect on condenser performance. The data spanned 25 to 75% load with up to 8% volume fraction of CO2 (based on the void volume of the condenser) To illustrate at 70% load, the condensing temperature was increased 2.3°C with 5% noncondensibles. The additional condensing side resistance at this condition is 2.2 times a water side fouling resistance of 4.4 ' 10--5 m2 -- C/W. At 70% load, 8% noncondensibles cause the compressor power increase of approximately 6% over that for zero noncondensibles. The experimental results are compared with predicted values using an analytical model.