Safe And Efficient Chimney Use - Thermal
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Safe and Efficient Chimney Use

During the Christmas season we hear an awful lot about chimneys and how a certain large, jolly man dressed in red squeezes his way down them on Christmas Eve.  Other than that, what else should we know about using our fireplace and chimney safely and efficiently?

Furnace Flues

  • A chimney typically has multiple flues in order to accommodate the fireplace, furnace, and water heater.
  • If you have a furnace that is below 90% AFUE Efficiency it will vent through the chimney.  The chimney allows the carbon monoxide to exit the home, and the flue should be opened anytime the appliance is running.  Typically in homes you are unable to close this flue.


  • Your flue or damper should be open anytime you are using the fireplace.
  • Many dampers have chains labeled “C” for closed and “O” for open that hang down into the fireplace so you can easily tell if it is open or closed.
  • If this is not the case with your damper, there are other ways to determine whether or not it is open.  You can see if you feel the outside air, or during the daytime look up the chimney to try and see the outside light.
  • There may be a time when you are sure the flue is opened, but you cannot see the outside.  If this is the case, your flue may be blocked by fallen branches or birds’ nests.
  • When the fireplace is not in use, the damper should be shut so as not to unnecessarily waste energy.


  • A chimney should be cleaned out every 5-10 years in order to prevent the build up of creosol.
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