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Field Test Best Practices: A Resource for Practical Residential Building Science

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Sealed Combustion Gas Water Heater

Sealed combustion gas water heaters, also known as direct vent gas water heaters, are similar to open combustion gas water heaters, but with restrictions on the air flow. In these water heaters, the inlet air flow to the burner is controlled to ensure the proper fuel-to-air ratio and the exhaust vent is also sealed between the water heater and the outside. This typically means that the system requires a fan or blower to pull the exhaust gases outside. The advantages to a direct vent system are that the combustion process is optimized and is more efficient. The entire system is sealed, so it can also be better insulated, which in turn improves overall system efficiency. There are higher installation costs with this type of water heater and the energy use of the blower must also be factored in.

Recommended instrumentation for a sealed combustion gas water heater field test includes: