fireplace smoke

MI - Michigan, United States   

My nephew has two fireplace in his home on separate flues. 

Also the hot water heater and the furnace have separate flues and are in the same chimney structure. 

When he builds a fire in the main floor fireplace smoke comes down the basement fireplace flue and smokes up the house.  on top of the chimney is a slab on concrete which is raised above the flues by about six inches.  it covers the entire chimney though raised at least six inches. 

It is supposed to keep rain from getting in the flues.  Is this what is causing the rpoblem? 

Have you ever seen a chimney with this on the top?



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by ChimneyChick | June 08, 2015 ChimneyChick's avatar
Midland, Ontario

very common practice to put a full concrete rain cap over a large chimney.
What you are experiencing is a convection current of smoke, hot smoke rises, hits the concrete cap and then the cold surrounding air pushes it down the other chimneys.
Normal heat cycling hot air rises, cold air descends to take the place of the evacuated hot air.
You could stop this by putting a top sealing damper cap on the basement fireplace so that when the upper is in use nothing can get down the other flue channel.

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