Vent Damper

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Automatic Vent Damper- A device installed in a furnace or boiler's venting system to restrict the loss of heat after the furnace or boiler has been shut off. Vent dampers are usually used in conjunction with an intermittent ignition device (IID), but can be used with standing pilot flames as well. Vent dampers often ship on new furnace and boiler models, but it is possible to retrofit older models as well.

Honeywell and Effikal both sell American Gas Association-certified vent dampers.