Expert: James Ball - 11/9/2008

Question
QUESTION: Hi..
I have a large brick, double sided fireplace with opennings of approximately 32"x20" on each side, and a 14"x14" square flue. We installed glass doors on both sides. When we have a fire, smoke comes into the room unless I leave only on door open (a 16"x20" openning). I'm trying to determine why this is occuring. I don't know if it was built properly in the first place. We're not the original owners of the house. The depth of the hearth is 41" (this is the distance between the doors) It has an 8" I beam across the middle, 28" high. The I beam is the centre support for 2 dampers- one for each side. Are all of these dimension a proper design? I think that the I beam is causing poor upward air draft, and may be too low versus the top of the doors? Can you let me know if it was constructed properly, and any ideas on reducing the smoke that gets into the room?

ANSWER: Hello Mark, lets start with are both dampers open completly? is the chimney tall enough?
Then if the fireplace works with the door open to the out side then you have a negative pressure issue, that is hot air raising in your home (and getting out through the attic vents, doors, lights) your house is a better chimney than your chimney. Also kitchen/bathroom exhaust fans, cloths dryers and the furnace all take house air out of the house (mechanical negative pressure) your house needs make up air, perhaps a open window in the basement? Or stop the air from getting out the attic.
I would have a local Certified Chimney Sweep (www.csia.org, there you can look up by zip code to find one near you) take a first hand look at what you have.good luck, keep me posted
James

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

QUESTION: Hi.. thanks for the help. a follow up question, in case this helps. Remeasuring, I found that the top of the door opening is only 3.5" lower that the damper/center I beam. So I've noticed that the smoke swirls around under the I beam, and then floats out into the room, because the top of the door opening is nearly the same elevation as the underside of the I beam. From the drawings on design that I've found,they recommend that the damper be installed at least 8" higher than the top of the fireplace opening. I think this is so there is a short "wall" above the opening to encourage the smoke upwards. Is that correct?

Also, good point about the chimney height. It's in the center of a sloped roof, with the minimum standard slope, and about 8 feet from the roof peak. The top of the chimney is only about the same elevation as the peak of the roof. I thought that the top of a chimney was supposed to be at least 3' higher than a nearby roof peak? Is that correct?

Again, thanks for all the help...

Answer
Welcome back Mark, yes 8" minimum above the lintel to the throat of the damper. and the height should follow the 3' (3' up from where you break the roof line) 10' (go in a 10' circle if you don't hit some thing you are ok, if you do then keep going up until you don't) then 2' (minimum) above that.
have that certified sweep take a look and they might offer suggestions on how to live with it or fix it.
James