Separation efficiency and peak capacity are important to analyze complex samples (e.g., peptide mapping). They depend on column plate number, system performance, and column temperature. In this article a new binary biocompatible UHPLC system is described that provides two column thermostatting modes, namely forced-air and still-air. For complex peptide mixtures of monoclonal antibody digests, still-air mode generates higher peak capacity compared to forced-air. Interestingly, the capacity gain is more evident at high temperature.