Furnace Vent Clearance to Wood or Combustible Materials Can Be A Fire Safety Concern if Too Close

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Published: April 27, 2014 Last Updated: April 5, 2015

6 inches or 1 inch ?

When homes are remodeled, new furnaces or water heaters are installed or the home has been reroofed, vents get moved or shifted a little and loose the proper clearance to combustible materials. When this happens, the vents may end up too close to wood or other combustible materials.

Fire safety

There are several different types of vent piping, including:

1. Metal single wall vent pipe

2. Metal Double wall vent pipe, often called “B” vent pipe

3. Transite – a whitish looking cementious pipe containing asbestos material. Early 1900’s to about 1975 it was used.

Each type of vent pipe has recommended clearances to combustible materials

1. Metal single wall generally requires 6 inches of clearance

2. Metal Double wall / “B” vent requires 1 inch minimum clearance

3. Transite generally requires 1 to 3 inches depending on various factors.

Trim back the wood, shift the vent or ….

Correcting this condition is often done by cutting back the wood that is too close to the vent pipe so that there is proper clearances.  If the vent is a single wall vent, then cutting back the wood or switching the single wall to a double wall may make this task easier. At times the vent can be moved or shifted over a little, to get the proper clearances.

Who to consult? Qualified handymen, plumbers for water heater vents and HVAC contractors for furnace vents.

Home owners may at times trim back wood or re-position a vent themselves. Water heater vents may be re-located or adjusted by plumbers and Furnace vents may be corrected by HVAC contractors. Also, qualified handymen can generally do this type of work as well.

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About how much do I expect to pay to move the vent or cut the wood around the vent. Thank you

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