During a major wind storm, a branch of an oak tree (which was undeniably
too close!) knocked the concrete cap and about 2 bricks off the top of my
chimney. This chimney serves an elderly oil furnace and a gas HW heater.
I intend to rebuild the chimney as soon as weather allows, probably March
or April of '08. The chimney appears to draw adequately... it is approx.
35 feet from the boiler breeching. I will prune back the offending branch
next week. Is there a major danger to leaving the chimney like this until
the weather improves enough to take it down to the roof level (pitched) to
re-build?
Smoke Free Masonry Chimneys
Summary: Smoke free masonry fireplaces can be achieved. Firebox width, height
and depth is now easy enough to calculate. Your builder can determine
the needs of your room versus the output of your fireplace.
Related
Articles: Fireplace Design & Installation,
Fireplace Design & Dimensions
DEAR TIM: My husband and I just moved into a new home with a masonry fireplace. We started a fire and smoke rolled into the room. We checked the chimney for blockages and found none. The damper was wide open as well. What could be the problem? Our fireplace is three feet wide. Is that too small? Can you see anything else in my photos? E.G.
DEAR E. G.: Tell me, did your home construction contract include a strong warranty? You're going to need it. Your photos clearly show several major problems with your fireplace design and construction that are contributing to your smoking problem.
The combustion of wood in a fireplace is very complex. The exhausting of smoke and toxic gases from the fireplace is controlled by three major factors: air pressure, temperature difference between inside and outside air, and the fuel combustion process. Improper design and/or sizing of the firebox, smoke chamber, and your chimney can cause an imbalance which will lead to a smoking fireplace.
This is my own wood-burning fireplace. The firebox is built to exact standards including the hidden smoke chamber directly behind the wood mantle.
Several problems are obvious in your photographs. The height of your fireplace opening is too tall in relationship to the 36 inch width of the opening. Furthermore, your firebox appears to be too shallow. This puts the fire too close to the fireplace opening and your room.
Your three foot wide fireplace opening should only be 29 inches tall. The firebox depth should be 16 inches. This depth does not include the thickness of the decorative brick which faces your fireplace. The distance from the floor of the fireplace to the bottom of the damper should be 37 inches. The smoke chamber, the area between the damper and the first flue liner, needs to be a minimum of 27 inches high.
Speaking of flue liners, I think the mason installed one that is too large. In your case, it should have inside dimensions of very nearly 10 inches by 14 inches. Smoke has to push the heavy, cold air up and out of the chimney. An oversize flue liner can make this a difficult process. What's more, my tables indicate that the minimum height for your chimney should be 21.5 feet. That measurement is taken from the top of the last flue liner to the floor of the fireplace.
As much as I hate to say it, I'm afraid that your entire fireplace and chimney need to be reconstructed. The two week process will be long forgotten after the smoke clears.
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Comments:
R. A. Broder, AIA 26 Nov 2007, 14:07
ATB 26 Nov 2007, 17:29
Not since you said you will be taking it apart in five months. Mother
Nature may assist you slightly in the meantime.
Maaz 08 Dec 2007, 05:49
Hi,
I am currently in a dilemma on whether to get an open fireplace using wood and coal, however the local council have said the area I live in a smoke free zone. I can of course by smokeless coal but would also like to burn logs. Is there something I can do to the chimney so that the amount of smoke is limited. Thanks for your help.
AsktheBuilder 08 Dec 2007, 07:18
Maaz,
No. If you want less smoke, you must burn everything in the fireplace. This is usually done by introducing massive amounts of oxygen into the fire much like a blacksmith does with a bellows. The only downside is you will probably burn down your house. Most fireplaces are not designed to be steel-mill blast furnaces.
Kevin E. Gage 07 Jan 2008, 07:08
Hello. I have read the various articles on smoking fire places and recently
extending my chimney to see if I could eliminate the back draft. It did not
work. My fire place has the following dimensions - front width 64", height
42", depth 23", rear width 29". The damper is 42" x 7". I also have a
copper extension the full length of the fire box.
It appears the smoke is drawing from the center but enters the room from the edges of the fire place. Any suggestions to fix this would be appreciated. Kevin
AsktheBuilder 07 Jan 2008, 07:36
Kevin,
I have another column about Fireplace Design that has a table of all of the dimensions and their relationship. Search and discover it. See if your fireplace has been built correctly. Be sure to read what I say about the smoke shelf and its height above the fireplace opening.
Jason 11 Jan 2008, 02:01
You could opt for a Masonry Heater which is smokeless or near smokeless. It
is designed specifically to burn cordwood quickly and competely...
Lee 14 Jan 2008, 23:16
Hi,
I live in a 1850 colonial with 4 chimneys. Each has been rebuilt and lined with what appears to be 6" round galvanized pipe, then back filled with concrete. Each chimney has 2 flues 1st/2nd floor openings. Have had problems with all first floor openings smoking. Haven't checked 2nd floor operations. Chimney sweep suggested removing caps (bluestone)to create more draft. No change. Had mason take a look and declared no smoke chamber/or had been filled with concrete? Sweep says maybe should remove all piping as flue is constricted and too small for 32wx31h firebox (rumford). Mason says major rework necessary, no way they will work the way they are. What's going on?
AsktheBuilder 15 Jan 2008, 06:46
Lee,
I need you to read ALL of my chimney and fireplace columns. You will discover one that has a fantastic table in it that tells you the proper flue size for your fireplace as well as the proper firebox sizes. I think the mason is right - the entire design was ruined by the idiot that installed the metal liner. You will soon discover the importance of the hidden smoke shelf and chamber when you read my columns.
Cory 07 Feb 2008, 11:20
Hi,
I'm building a log cabin about 22' x 16'. What size fireplace would work best for this space. And how big shuld my chimney, damper and flue be. View all comments |
