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Condensing Gas Water Heater

Condensing gas water heaters come in two forms: a storage tank type and tankless. The principle behind both is the same: The hot exhaust gas produced during the combustion of natural gas is used to heat the water. This is done by making the exhaust pipe in a shape with more surface area, thus, promoting heat transfer. A diagram of a tank-style condensing gas water heater is shown in the figure below.

Tank-type condensing gas water heater. The exhaust pipe is coiled inside the tank to promote further heat transfer. Credit: Energystar.gov

Condensing gas water heaters use more of the heat generated by burning natural gas and are more efficient than standard gas water heaters. According to the EnergyStar® website, storage type condensing gas water heaters are 30% more efficient than high efficiency gas water heaters. Condensing tankless gas water heaters can be even more efficient since they eliminate tank losses but have the same consideration requirements as any other type of tankless water heater. Another benefit to condensing water heaters is that the exhaust is much cooler than in standard gas water heaters since all the heat is removed, so the exhaust pipes can be PVC and much smaller in diameter. This makes installation easier and removes one hazard (a hot exhaust pipe) from the house.

Recommended instrumentation for a condensing gas water heater field test includes: