The authors carried out questionnaires and field measurements on the hot water consumption and the performance for CO2 heat pump water heater in houses. The new type CO2 heat pump systems were set up in 7 houses and the measurement was started from September 2008. In this paper, the performance and characteristics of different heat pump systems were considered based on the results under running condition in middle season and winter. Monthly and daily fluctuations of hot water usage and heat pump performance were discussed. Moreover, the general opinion of heat pump water heater system was shown by user survey of website.
