The invention relates to a water heater comprised of a cylindrical tank 18 which has a central flue 20 that is mounted with the cylinder axis 40 vertical. The water heater further includes a gas burner 22 provided the base of the tank 18, which burns a gaseous fuel so as to discharge heated gases up...http://www.google.com/patents/US6378777?utm_source=gb-gplus-sharePatent US6378777 - Natural draft water heater
