fireplace, what give with smoke

[Chester]

<font face="Verdana, Arial" size="2">Originally posted by fahnoe:


The basement fireplace had the same opening, just a taller chimney, so I figured I could either add height to the chimney (expensive) or reduce the aperature with a set of doors (less expensive). The addition of doors solved my problem: even when they're open, the frame reduces the opening enough to draw properly.

--Larry</font>

Interesting comments, but from my experience it goes even further. In my basement I have a wood burning stove with two cast iron doors. All performs well, and it will draw perfectly with the doors open for the first couple of hours or so. When the chimney reaches operating temperature there is a hugh reduction in the draft effect and you can have wisps of smoke coming out into the room with both doors open. Close one door and it will operate with out smoking again. But, to return to the same draft effect that was there upon start-up (everything cold) you need one door closed and the other just cracked open. Have been told that in industry a similar thing happens to their boilers, so it looks to me like the chimney height is not the only consideration effecting the draft available.

[rockrat]

Ok, I have just about had it.

I have a nice big fireplace. It is a big wall of rock with a fire box constructed in it. I clean it out every year in the fall before the big cold.

So, I have learned that any outdoor temp over 40ºF results in a bit of a backdraft which puts some smoke in the house. It is just enough that you can't see it but your eyes will let you know.

Tonight, its about 38ºF outside and falling. I stoked up a fire around 6:00pm and enjoyed a beverage with a book near the heat. The cats were happy warm and I was fine.

About 8:30 I threw a log on and noticed it was smoking a bit. So I moved the log to the back to keep the smoke drawing up the flue. Seemed to work well.

But within about 10 min, I smell a bit of smoke. I poke the logs and move things aroun a bit. I even go and crack open a window at the far end of the room. I feel a draft comming in and I watch the smoke roll up the flue.

It all clears out and I shut the window. Back to life and it will probably fine now.

So what gives? Did I let the flue temp drop? I try to keep a good fire burning. Normally, it gets so hot I have a bit of trouble getting near it without gloves on.

It seems to do this every once in a while.

What am I missing?

rock

[aboard_epsilon]

For heat and fumes to go up the chimney it needs to carry some room air with it.
so the room must be vented .
the fire also consumes air from the room .....this must be replaced from somewhere
some people put a vent in from the ouside with a tube that comes out underneath the grate..so you dont get drafts of air being replaced in the room.

also caution many people have died from having unvented fires burning in houses.

all the best...mark

[deltap]

Does the fireplace have its own outside air supply? If it worked when a window was opened, maybe the house is too tight. All that volume going up the chimney may create a negative pressure in the room causing draft to be lazy.

[railfancwb]

Our fireplace seems to draw better when I've kept a bed of ash (about 2") under the grate -- unless I forget to open the damper. Charles

[snowman]

your chimney may not be tall enough either.

my brother in law's chimney needs another two feet added to it, it doesn't stick above the top of the house high enough.

-Jacob

[big-dipper]

Lots or air going up the chimney, needs to come from somowhere (like your open window). I don't believe the flue temp is the problem, your house may be too "tight", the fire needs to breathe. I got a leaky house, opening the glass doors on the fireplace, it's almost like there's an air hose balsting the fire! Smoke goes away fine with the doors closed.

[HWooldridge]

We have the same problem on occasion and you can sometimes see the smoke rolling out the front of the opening. Soon, there is a haze of smoke thoughout the entire house. I have found that good healthy flames help - a big log will smoke unless there is a real good bed of coals under it to keep the flames going. The fire also needs to be against the back of the fireplace so the box heats up and causes it to draw. I made a grate that keeps the coals about 3 inches off the hearth and push the logs well back in the grate.

You might try a couple of things - a lot of small logs will make more flames. Another suggestion is a fireback, which is a cast iron or steel plate that gets warm and radiates into the room plus that heat helps carry smoke away.

[rockrat]

It's an old house and I always thought that there were enough gaps around to pull air from the outside. If I shut the front door with the back door not latched, it would not move. My buddies house is tight. Do the same there, and the back door will fly open. I know, there are volumetric claculations that could probably explain the difference.

I do have the ability to get under the firebox. I might try and install a quick little air supply from outside and see what happens. Might make all the difference in the world.

Ok, major spelling errors tonight, maybe lack of oxygen. Edit....

Yes, I opened the little window back up and the fire is almost out. I think we are safe tonight. I know how you tool hounds are.
Just waiting for me to give it all up.

Ha ha ha..

[This message has been edited by rockrat (edited 03-02-2006).]

[Carl]

Some nights our wood stove burns so easy and so hot that I have to close the damper quite soon to keep it from getting so hot that you can't get near it. Other nights it is extremely hard to keep hot. Some nights it is the wind backdrafting it. On some still nights though I always thought it might be the barometric pressure causing even thinner air than we normally have up here at 9500 ft. elevation.