Insulation clearance on water heater flue?


Old 07-14-10, 09:43 AM
Thread Starter
Join Date: Jul 2002
Location: Ca
Posts: 743
Insulation clearance on water heater flue?

Hi all,

I added cellulose insulation to my attic and I noticed that the previous insulation (blown fiberglass) was in contact with the water heater flue. I almost certain the flue is single wall, about 3 inch diameter. House was built about 12 years ago. Do I need to provide clearance?

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Old 07-16-10, 09:10 AM
Join Date: Nov 2001
Location: USA
Posts: 1,873
First and foremost you have to check with your local building officials. The first place I would go if I was you is the local fire department.

Blown in fiberglass does not catch fire but it melts. Cellulose has a variety of chemical additives and one of them makes it fire retardent. Most use a chemical that requires a direct flame to ignite the cellulose, however, once you move the flame away from the cellulose the fire goes out. Some use chemical additives that even with a direct flame the cellulose will not ignite. Check with the manufacturer which type you have.

Some towns, regardless of the type of insulation used, require clearances around combustion gas flues. Again you should check with your local building officials.

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