Abstract: This paper focuses on the effect of supply temperature,water flow velocity,and tube spacing on the hot water floor heat exchanger through experiments.The testing experiments were carried out in four rooms with the same two-pass style arrangement and different tube spacings in an office building in Beijing.Heat flowand floor surface temperature were analyzed and compared as the supply water temperature and water flow velocity were varied independently,and non-uniformity of floor surface temperature in different tube spacings was determined.The optimal ranges of supply water temperature,water flow velocity,and tube spacing for Beijing's office buildings were presented.