Chimneys

Published on January 26th, 2014 | by Henri

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Flue must be lined when switching from gas to wood heat

Q.    We are thinking of adding a wood burner to our existing forced air duct work. We currently have a single-flue brick chimney with no tile liner. Is it necessary to line the chimney if it is in good condition and services no other appliances, such as the water heater or gas furnace? The chimney goes through the center of the house.

A.    Are you planning to disconnect the gas furnace and replace it with the wood burner? Or is there another flue for the furnace? Or a newer furnace vented through a wall? The NFPA (National Fire Protection Agency) no longer allows more than one appliance per flue, so you are fine since you mention the flue in question is not serving any other appliance.

But of greater concern is what will happen to the chimney flue when you start burning wood. Burning wood, even dry wood, results in the formation of a very corrosive chemical called creosote. It will literally eat the bricks and mortar out of your chimney leaving black creosote to ooze out and stain everything.

Yes, you absolutely need to have the chimney lined with the appropriate-size stainless steel liner or concrete forms. The person doing the work may also suggest pouring insulation between the brick chimney walls and the stainless steel liner in order to keep the gases even warmer as they ascend the chimney. The fact that the chimney is in the center of the house is a definite plus, as the main body of the chimney will remain warm. This will be helpful in reducing — but not eliminating — the formation of creosote and in providing a better draft for the stove.

You should also use ACS (Anti-Creo-Soot) on a daily basis, following the instruction on the spray bottle. You should be able to buy ACS from a stove shop or a chimney sweep.

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