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Flue or Vent Dampers on Boilers

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  rev. 2008-11-25        

Existing Conditions

The existing heating boilers are piped in such a way that water flows evenly through all boilers whether they are firing or not.  These boilers have atmospheric burners, meaning that air from the boiler room flows by convection (without a fan) into the bottom of the boiler, past the burner and heat exchanger, and out through the flue.  If the burner is firing, that air combines with the fuel to allow combustion.  If the burner is not firing, there is still a significant air flow.  When a boiler is not firing, heating water is still being pumped through it, so the heat exchanger acts as a giant radiator.  The air passing through the boiler picks up heat from the heat exchanger, and passes up the flue and outside.

Retrofit Conditions

New atmospheric boilers can be factory-equipped with flue dampers that shut when the boiler is not firing.  The dampers block the wasteful migration of hot air up the flue.  This type of damper arrangement should be installed on the boilers at this facility, and electrically interlocked with the burner controls for safety.

Further Benefits



Application Details


Issues and Concerns

At the time of this writing we believe that this type of installation is legal and in conformance with current building safety standards.  However regulations dealing with boiler flues and vents are continually changing.  Before proceeding, it will be important to confirm with the local building safety authority that the installation will be approved.


This recommendation is in accordance with Section 6.3 Heating, Ventilation and Air-Conditioning Systems of the ASHRAE Standard on Energy Conservation in Existing Buildings.  ASHRAE Standard ANSI/ASHRAE/IESNA 100-1995 – Energy Conservation in Existing Buildings is an approved standard of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., the Illuminating Engineering Society of North America and the American National Standards Institute.



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