A representatively pumpless water heater system has an instantaneous water heater coupled in series with a storage water heater by piping circuitry incorporating a bypass valve and a mixing valve and useable to route pressurized incoming cold water sequentially through the instantaneous and storage type...http://www.google.com.hk/patents/US7298968?utm_source=gb-gplus-share專利 US7298968 - Pumpless combination instantaneous/storage water heater system
