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Energy Efficient Condensing Side-arm Gas Water Heater

Lawrence Berkeley National Laboratory

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Technology Marketing SummaryJames Lutz of Berkeley Lab has invented a gas water heater that promises to be up to thirty percent more efficient than conventional gas water heaters. DescriptionThe design replaces the traditional central flue with a side-arm heat exchanger, thereby eliminating standby energy losses that occur when heat is transferred from the hot water to the cooler central flue when not actively being heated. The heated water is transferred from the heat exchanger to the tank by thermosiphonic action, or through heat-induced density changes in the water acting as a driver. No mechanical pump is necessary.

Integral to the side-arm component is a simple system for capturing heat from the water vapor in the combustion products – a second source of energy inefficiency in conventional design ­– and collecting the condensate so that it doesn’t exit through the venting system. This process involves using a small, low power electric fan and the cold water at the bottom of the water tank for cooling. A basic electric water heating tank can be adapted to the Berkeley Lab design.

This invention could be combined with an existing low-emission burner technology to produce a revolutionary clean burning and efficient gas water heater.
Benefits* Promises to be ~ 90% efficient; 30% more efficient than conventional gas water heaters
* Could be manufactured by adapting a basic electric water heater tank
Applications and IndustriesResidential gas water heating Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Application 20090188447
Condensing Side-Arm Water Heater
An apparatus for providing a condensing side-arm water heater with improved efficiency. The condensing side-arm element recirculates exhaust gases into heating the cooler part of a water heater tank by the thermosiphon (or buoyancy) effect in a counterflow configuration, thus increasing efficiency of the water heater.
Lawrence Berkeley National Laboratory 06/26/2007
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
IB-2198DevelopmentAvailable - Available for licensing and collaborative research. 06/15/201006/24/2010

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To: Shanshan Li<>