Expert: Bart Ogden - 1/21/2006

Question
--Thanks Bart,

That was very helpful.  I am considering an exhaust fan and could do the installation myself.  However, could you tell me what problems I might encounter if I just opened up the other flu tile in this double-flu chimney?  In other words, does having an over abundance of flu area cause problems?

sincerely,

Jerry Kerr






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Followup To
Question -
Hi Bart,

My double-sided fireplace often puts smoke into the house, but always into the same room.  The fireplace openings are 672 sq. in. in the family room, and 816 sq. in. in the living room, which is the room that takes on smoke.  Both sides have glass doors that I can adjust, but it seems that no matter how I adjust the doors on the larger sized opening, I still get smoke into that room.  I always keep the doors on the smaller opening all the way open.

This happens almost everytime I have a fire, but I won't have any problems until I get a log that is especially smoky, them I don't seem to have enough draft to keep all the smoke going up the chimmney.  I have tried cracking a window near the fireplace, in the room that takes on smoke, but this did not help.  Here are some specs. on my situation:

- flue size is 10 x 14 flu tile
- there are actually two of the above mentioned flu tiles in this chimney, but one is sealed off at the chimney top with concrete, and at the bottom with metal plates.  Previous owner says it was built that way and was never tried with both flues open.
- My chimney is about 26 ft. tall (Measuring from above the damper).
- My house has a crawl space underneath, is 30 years old, and is not especially air tight, but its not too bad either.

Should I try opening up the other flu tile.  According to the way I do the math...one, 10x14 flu tile satisfies the 1/10th rule.

Or, should I buy a chimney extender that might give me more draw?

Thanks for your time,

Jerry


Answer -
Hi Jerry,
    According to my math the flue is incorrectly sized.  The INSIDE Dimension of the flue tile should be at least 148.8 square inches.  This flue tile at 10x14 reported I.D. is only 140.0 inches at a best case scenario.
    If, and this is a big if, the flue is perfectly straight, perfectly smooth on the interior and has no restriction in the way of an undersized screen on a chimney cap, the flue might work - provided there are no pressure differentials in the house.
    Most 2-sided fireplaces suffer smoking problems of one sort or another due to what I've described above.
    It's very likely that the only way you'll solve this is by one of the following:
    1.  Solve the pressure differential problem in the house (particularly if it's a multi-story house)
    2.  Install an Exhausto chimney fan on top of the fireplace and physically exhaust the combustion by-products.

    As far as adding a chimney extender to increase draft, that only works in certain specific conditions and circumstances.

    I've fought these for years and, in most cases, it's simply easier to instll the fan which is a guaranteed solution.

    If you need a fan, we carry those in stock in our warehouses and can ship to you.

Good luck with your project and thanks for using AllExperts.Com!

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

Answer
Hi Jerry,

The answer to your question is "Possibly".

If the smoke chamber area is not properly shaped and transitioned into the flue openings you can actually cause turbulence and smoke eddies at that junction which can inhibit draft.

Although you would theoretically be increasing flow, the inhibition of draft might be an issue in some circumstances.

Also, if by opening the other flue up, if it is not properly transitioned, you could be letting combustion byproducts in behind the other flue system.  This could lead to those byproducts migrating to the living space or to an inaccessible area that could not be properly maintained.  Either of those areas could lead to life and/or property damage.

If you can do the fan installation yourself, you'll be able to take care of the problem you're experiencing without the time and materials involved in a "possible" solution.  

Good luck with your project and thanks for using AllExperts.Com!

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