Hello Tim,
I just built a house with a very large “cooking” masonry fireplace. The opening is 6’ long by 4 ˝’ high, the top is arched. I have days when the fireplace works wonderfully and other days you can see the smoke going up but then it swirls and comes out at the very top. If I keep a door slightly open across the fireplace for a while it does not do that. Other days I don’t have to open the door, it works great for days. Then all of a sudden the next day I will have the smoke billowing out. Why does it do it some times and not other time? Help!!
Andrea Stephens
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Andrea,
Fireplaces smoke because they are not built right. There can be many different defects: improper firebox design, missing smoke chamber, chimney flue too large, chimney height too short, etc.
Many people do not realize there are distinct relationships between the width and height of a fireplace opening and the shape, size and sloped faces of the internal firebox size of the flue and the overall height of the chimney. I have covered this topic in great detail in a past column and I have produced a table showing the size relationships in a past Builder Bulletin that is located on my subscription-based Premium AsktheBuilder.com website.
You can use the information in the table to determine if the fireplace firebox was constructed properly. If is defective, you are going to have to bite the bullet and get the builder to do it right the second time around.
Tim Carter
www.askthebuilder.com
W3ATB