At Mathis Sydney Plumbing and Heating Company, Inc., it`s never business as usual. You see, we believe the most important “product” we provide is your increased home comfort, safety and, ultimately, peace of mind. Beyond superior products and service, we adhere to and a set of you can count on… no matter what. Eternal Hybrid? and Eternal Condensing Hybrids work on the Counter Flow Principle. This is an opposite approach to the way industry has traditionally built water heating appliances. Unlike any other water heater appliance, Eternal has achieved the highest efficiency in the industry without sacrificing your comfort..