Oil fired furnace venting into the same chimney flue as a natural gas fired water heater.

Just the fact that oil burner and gas burner are sharing the flue is not necessarily a problem, as far as I know. You can't have solid fuel and gas/oil sharing the same flue.

My take on this and I have spoken with OIl companies on this is that the mixing of the exhaust gases creates an acid which is flamable and causes deterioration of the flue liner.
I find it all the time and was just wondering of everyone elses finds and comments.

It's allowed. If all else is right I don't raise an eyebrow.

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Chad Fabry, Rochester, NY
StructureSmart Home Inspections, Inc.
www.structuresmart.com

thanks Chad, any links about it or is that your take on it.?

Interconnection is allowed per NFPA 211 as long as you meet several criteria:
-There are primary safety controls on both appliances
-There is sufficient draft available for the sale operation of both appliances
-All appliances are located in the same room

In short, it has to work.

Gas combustion produces hydrochloric acid while oil produces sulfuric acid. Both product traces of other acides. Acids are not considered combustible but are corrosive. In addition, the higher the sulfuric acid concentration, the higher the dewpoint. This means burning lower grade #2 oil results in more condensation of acids. Both fuels will cause corrosion. I'd worry more about the liner, vent connectors, makeup air, etc. than interconnection.

John was correct: solid fuel cannot common vent with anything else including other solid fuel appliances.

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disgusted with some people on this forum. Out of here!