help: fireplace has a smoke problem

[lobolmart]

hello,

i bought a 2 story house and it has a fireplace in the living room.
one big problem though...it doesn't work unless a window or a door is open in the said room or otherwise smoke starts building up over the fireplace. the fireplace can't really heat up the room due to the required airflow.

i need some help to fix this, so i've provided some schematics of the whole installation (sorry, can't take decent photos ATM). my units are metric.

*) this is the house overview:

in this view the back of the house is pretty much north - i.e. where most of the wind is comming from. i haven't calculated the roof angle, but it's less than 45 degrees.

https://dl.dropboxusercontent.com/u/1627980/fireplace/fireplace_image1.png

*) this is the fireplace
it's a weird one...
the base is a quarter of cylinder with radius of about 90cm.
the "exhaust" (not sure about the term in english) is conical, yet not that good looking.
the skeleton inside is probably a metal net to provide a shape. the filling is probably slaked lime, sand and cement + something else,
while the coverage is painted plaster.

what happens is that whenever i start a small fire that produces slightly more smoke,
there doesn't seem to be enough "pull" for this smoke to leave the conical exhaust and it's starts to enter the room.
...if i open a window or the door slightly the smokes goes through the exhaust into the chimney, but the room starts getting cold.

https://dl.dropboxusercontent.com/u/1627980/fireplace/fireplace_image2.png

*) this is a view from the top - looking down the chimney

it's a double chimney...my guess is that the second hole was planned for the bedroom above the living room but it's currently unused and completely closed bellow.

there are these wierd brick cavities between the two chimney holes, which seem more like a construction imperfection and not like something planned.
these seem to go all the way down between the two chimeny holes.
hot air seems to go though the cavities!

https://dl.dropboxusercontent.com/u/1627980/fireplace/fireplace_image3.png

notes / questions:

*) i ran a stone tied to a rope through both holes to make sure they are clean!

*) i'm pretty sure that the chimney needs to be taller, as currently it doesn't follow the "2ft" rule (0.5 / 0.6m)?
should that be the first thing to try?

*) given the "weird cavities" between chimney holes, would those affect the air flow in a negative way?
i've tried closing the second unused chimney hole from the top with a metal plate, but it didn't change anything.

*) someone told me that the chimney should not be a T-shape on top. any idea why is that?

*) it feels like the base of the fireplace is too low, while the cone is too high. would changing that make any improvement?

*) is the "cone" shape a bad idea for an open fireplace in general? perhaps this one needs a complete redesign?

thanks for any ideas!
l.

 

[jatoxico]

You are probably suffering from the stack effect. You can look it up for more detail but with the fireplace on the lower level, air in the house is rising into the second floor and attic due to pressure and temperature differences. Air then escapes out the top of the building. The building is trying to make up for the lost by pulling air down the chimney. Opening the window alleviates the pressure difference and provides another source for the lost air.

The problem may lessen as the flue warms up but w/ and open fireplace (hard to get much heat even when working well) and an outside chimney it may be a tough go.

Stack effect is not always easy to overcome but make sure there are no obvious sources of air loss like clothes dryers, kitchen or bath fans on at the same time. Also any attic stairs etc should be well sealed.

 

[begreen]

If the two flues are connected with those cavities then yes, they could be spoiling draft. They would cause air to be pulled from the adjacent flue instead of from the fireplace opening a the base of the chimney. It would be good to drop a camera down then (secured to a rope) to inspect what is happening down the flue.

Where in Bulgaria are you? If this is a rural area is there any inspection at all on construction? And in some other areas inspectors are simply paid off.

 

[lobolmart]

You are probably suffering from the stack effect. You can look it up for more detail but with the fireplace on the lower level, air in the house is rising into the second floor and attic due to pressure and temperature differences. Air then escapes out the top of the building. The building is trying to make up for the lost by pulling air down the chimney. Opening the window alleviates the pressure difference and provides another source for the lost air.

The problem may lessen as the flue warms up but w/ and open fireplace (hard to get much heat even when working well) and an outside chimney it may be a tough go.

Stack effect is not always easy to overcome but make sure there are no obvious sources of air loss like clothes dryers, kitchen or bath fans on at the same time. Also any attic stairs etc should be well sealed.

thanks for the answer,
indeed this fireplace seems very inefficient. even if i can't test it fully as i need to have a window / door open at all times.

i may have to consider complete redesign or introduce air in some way near the fireplace.

 

[lobolmart]

thanks for the response,

If the two flues are connected with those cavities then yes, they could be spoiling draft. They would cause air to be pulled from the adjacent flue instead of from the fireplace opening a the base of the chimney. It would be good to drop a camera down then (secured to a rope) to inspect what is happening down the flue.

yes, i can imagine. they are connected and it seems like it's a construction imperfection - i have no idea why would someone leave these. i can fill up some near the top, but with a flashlight i can see these going all the way down and i can't fix that without destroying the whole chimney - i.e. ~6m+.

do you think that covering the unused flue would help the one which is used to pull more?

Where in Bulgaria are you? If this is a rural area is there any inspection at all on construction? And in some other areas inspectors are simply paid off.

near Golden Sands. the house is 1km away from the coast of the Black Sea. its *very* windy, moist and cold during the winter.
they would inspect the roof height, but i doubt they would care much about the chimney being 1m higher than any regulation.

in fact, i never heard someone being regulated about chimneys, so i wouldn't be surprised that there is no chimney regulation in the area.

edit: i can probably make the chimney quite high if that would help.

 

[begreen]

The fireplace will never be a good heater. As the fire dies down it will continue to suck warm air out of the house. You might try capping off the unused flue to see what happens, look for a cleanout door too, that can be a source of draft spoiling leakage. Even if blocking off the unused flue helps I don't like this arrangement. Those crossover passages are going to be uncleanable creosote traps.

In the long term you might want to consider other options. One might be to drop a stainless 150mm liner down the fireplace flue and have the directly connect to the rear vent of a wood stove. This might take some demolition of the conical hood to accomplish, but in the end you would have much better heat.

I was in Bulgaria about 8 yrs ago, beautiful country. We only made it as far east as Veliko Tarnova, never got to the Black Sea. Would like to return at some point.

 

[lobolmart]

The fireplace will never be a good heater. As the fire dies down it will continue to suck warm air out of the house.

i did get the suggestion to install a large stove, remove the cone shape and turn this into a closed design.

You might try capping off the unused flue to see what happens, look for a cleanout door too, that can be a source of draft spoiling leakage. Even if blocking off the unused flue helps I don't like this arrangement. Those crossover passages are going to be uncleanable creosote traps.

ok, will do.

In the long term you might want to consider other options. One might be to drop a stainless 150mm liner down the fireplace flue and have the directly connect to the rear vent of a wood stove. This might take some demolition of the conical hood to accomplish, but in the end you would have much better heat.

that's a very good solution to bypass possible issues from these cavities. i think this liner wasn't that expensive the last time i checked.

I was in Bulgaria about 8 yrs ago, beautiful country. We only made it as far east as Veliko Tarnova, never got to the Black Sea. Would like to return at some point.

my aunt lives in VT.
hope you find the time to visit Bulgaria again.

thanks for the valuable information.