Expert: Bart Ogden - 12/31/2005

Question
-------------------------
Followup To
Question -
We have very strong creosote/stale smoky smell in the room
(large room: 12' H, 23' L, 15'W) from fireplace (50"L, 40"H, 25"L)
when fire is NOT burning.   Smell only occurs days when
humidity outdoors is above 80%: is NOT related to wind speed or
temperature outside.  There appears to be downdraft in flue
(fireplace windy/cold even when flue closed: I am being told this
is because the flue is too wide for this size fireplace; round flue
is 15" diameter, chimney is 25' tall, in 1 floor room, situated on
outside edge of house built 1939).  Heating system is radiators
(water).   Is one solution to install a chimney cap with an
integrated lock-top damper to shut out the downdraft?   Thank
you very much for your attention to this query.
Answer -
Hi Jonathan,

You're likely experiencing a pressure problem in the house that's causing the fireplace flue to act as the make-up air source.

One partial solution might be to install a flue cap with an integrated lock-top damper, but in extreme cases, it's not going to be the final solution.

You'll still need to find out where the pressure problem is with the house.

I would suggest you visit www.csia.org and find a local CSIA Certified Chimney Sweep who is familiar with pressure testing and have them come out and look at your individual situation.

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

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney
Wichita, KS
www.homesafeks.com

Follow up question:
Hi Bart,
Thanks for the quick response.   The room is older, large, has old sash somewhat drafty windows, is built over a dirt crawl space and has radiator heat.  I understand from our building engineer that pressure problems are more likely in newer houses with small rooms and tightly sealed windows.  Would you agree, or could pressure problems arise for other reasons, and would they only arise during high humidity?

Answer
If the house leaks enough (too much) it can act as a better chimney than the flue.  Check for that as well as the termination meeting the 10-2-3 rule as well.  

I'd start there first to find the source of the depressurization.

Something's happening to cause the reversal.

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney
Wichita, KS
www.homesafeks.com