Chimney Back Drafting

[peteml]

Does anyone have any suggestions/comments as to why our chimney will be working just fine and then it will reverse and all the smoke will come into the house. We just had it cleaned and the cracks sealed. We can start the fire just fine, but sometimes the smoke doens't go up. There is no flue on the chimney either.

Thanks

[LazyPup]

There are many factors that effect the overall draft of a chimney. Basically a chimney functions by the basic law of physics that states hot air is lighter than cold air, therefore the hot air rises. As the inside of the chimney and flue get hot the rate of draft will increase proportionally. In the case of chimneys there is also a correlation between the internal diameter of the flue opening and the height of the chimney, the larger the flue diameter the taller the chimney must be to insure good draft.

If the backdrafting you are experiencing is only happening during the first few minutes after the fire is lit it is a result of cooler air in the chimney, and the problem should correct itself as the chimney begins to heat up. One trick here is to use a lot of small kindling that will produce a higher flame and increase the stack temperature faster to begin the draft effect.

If the smoke is backdrafting after the fireplace and chimney have had sufficient time to preheat you may need to add an extension on the top of the chimney to increase the draft.

[kactuskid]

You need a combustion air source to help in maintaining your draft. So, opening a window in the same room as the fireplace will provide enough air for you. Doesn't have to be wide open , but cracked at least a 1/4" -1/2" to allow the air through. Also make sure that no exhaust fans are running in the house while you have a fire going. (like a kitchen or bath exhaust fan)

Also, put a piece of crumpled up newspaper ontop of the log after you light it. Close the fireplace doors. The heat from the paper will start your draft off really fast. Then you can open the doors back up.

It would be in your best interest to have a fireplace liner installed inside your chimney, this would help in maintaining a proper draft and it would keep your bricks from deteriorating.

Also make sure you burn hard woods and keep the fire hot.

Here's a link that'll give you lots more details

http://mb-soft.com/juca/print/outsidea.html