Expert: Bart Ogden - 1/12/2009

Question
QUESTION: Hi Bart, I have had a chimney fire and I am somewhat surprised. I clean the chimney twice each year with a proper size brush. When I do I get all the loose flakes off and the chimney and connection to the firebox look clean.
Is it possible that my flue is too big? It is 10". Fire box is 43" wide by 24" high and tapers 19" back. The chimney is about 13" high. I had read that a flue that is too big can cause the draft to be too slow.

Thanks,
Ed Q

ANSWER: Hi Ed,

If you have a masonry fireplace and didn't clean the smoke shelf area thoroughly you left a potential fuel package in place for a chimney fire.

Before this system is used again, I recommend you contact a local CSIA Certified Chimney Sweep to do some on-site diagnosis of your problem and to conduct a Level 2 chimney inspection because of this sudden-occurrence event.  The system and flue tiles need to be inspected carefully to ensure that there is no damage.

You can find a CSIA Certified Chimney Sweep at www.csia.org.

The size of the flue has no effect on draft, only on flow, all factors being equal.  An oversized flue system can cause increased residence time and decreased stack temperature, which, in turn, can cause accelerated creosote accumulation.

I'm assuming you meant that your flue was 13 feet tall, not 13 inches tall as your post stated.  This flue height should not impact creosote accumulation substantially.

Thanks for using AllExperts.Com and good luck with your project.

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney, Inc.
Wichita, KS
Voice 316-265-9828
Fax 316-265-9890
www.HomeSafeKS.com

CSIA Certified Chimney Sweep #2653
CSIA Certified Dryer Exhaust Technician #10
NFI Certified Wood Specialist
NFI Certified Gas Specialist
NFI Certified Pellet Specialist
NFI Master Hearth Professional
NCSG Technical Advisory Council Member

---------- FOLLOW-UP ----------

QUESTION: Thank you for your quick response. My flue is a 10" round metal one. My chimney is in fact 13' and not 13" as I mistyped. I was hoping to be able to clean the chimney myself with the 10" brush I bought. I wanted to know if I must clean it down to shiny metal or scrapping the flakes off would suffice?

Ed

Answer
Hi Ed,

If you have a round metal flue, you should be using a round plastic bristled chimney sweeping brush sufficiently oversized to exert enough pressure on the flue walls to remove the existing creosote.  An up and down scrubbing action is the mode of operation.  Be extremely careful that you don't dislodge the inner or outer flue sections.

There is no need clean the metal flue walls spotless, but you must remove as much of the creosote as possible to prevent a chimney fire.

You must then remove any creosote from the fireplace or connector area.

You shouldn't see much more than dirty metal with brush marks when you're finished.

If you feel you need a professional, you can find a CSIA Certified Chimney Sweep at www.csia.org.

Thanks for using AllExperts.Com and good luck with your project.

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney, Inc.
Wichita, KS
Voice 316-265-9828
Fax 316-265-9890
www.HomeSafeKS.com

CSIA Certified Chimney Sweep #2653
CSIA Certified Dryer Exhaust Technician #10
NFI Certified Wood Specialist
NFI Certified Gas Specialist
NFI Certified Pellet Specialist
NFI Master Hearth Professional
NCSG Technical Advisory Council Member