Does a Shared Chimney Mean More Problems?

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In some areas, building codes allow more than one appliance to vent through a single chimney. Even oil and gas flues can sometimes use the same chimney flue. This can present some challenges, but a lot depends on the size of the flue as well as other aspects of the installation. A regular chimney inspection will usually reveal potential issues that you will be informed of, and we will help keep an eye on these issues over time during your regular chimney inspections.

Potential Shared Chimney Problems

With a shared chimney, two or more combustion gas producers in the building will vent through the same conduit. It is possible to create a large chimney with more than one flue. In such cases, the flues must be properly spaced and sealed to prevent leakage.

Venting gases from different areas through a single flue could very well be a violation of building codes. It is important to have individual flues for a heater and fireplace for example. Otherwise, gases produced by one appliance can leak into another area of the home. If you are using one heating appliance but not the other, gases can escape through the other appliance creating a danger for the occupants. If gases are coming in through the fireplace, it might be necessary to take the drastic step to seal it off. This should be a temporary measure as the fireplace may be needed at a later time. Here are some examples where hazards are created when more than one heating appliance uses a single flue.

  • A furnace, a basement water heater and fireplace on an upper level connected to a single flue
  • A home with more than on fireplace one different floors connected to a single flue
  • One flue connected to a woodstove and a fireplace on different floors
  • A single flue connected to more than one fireplace on the same level

Some of these situations may actually be building code violations depending on the area. Some of these are most likely to be found in older homes that have not been updated to current standards. This can be even worse in old homes with unlined chimneys. A blockage in the chimney flue could also lead to gases escaping through one area while a heating appliance is being used in another area.

As you would expect, more burning means not only additional gases, but quicker creosote buildup in many cases as well. It is possible for a chimney flue to become overloaded when too many combustion appliances are connected to it. If you live in an old building with a shared flue, talk to one of our CSIA Certified Chimney Sweeps about your options. We can advise you on the best way to proceed to make your home and chimney safer.

Give us a call at 610-626-2439 to schedule a consultation, chimney cleaning, or inspection. Schedule your appointment for cleaning and inspection soon to miss the post-winter cleaning rush.

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