Help - smell of smoke in basement when having fire in fireplace above


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Old 11-17-08, 11:51 AM
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Help - smell of smoke in basement when having fire in fireplace above

Whenever we light a light in our wood burning fireplace on the main floor, we can smell smoke coming out of the fireplace in the basement which is directly under the one on the main floor. The whole basements fills with the smell. Both are non-inserts and have separate flutes. Does anyone know why this is happening? We had both flutes cleaned and checked recently and nothing appeared wrong.
 
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Old 11-17-08, 02:36 PM
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Could be negative air pressure in the home. Open a window or door part way to see if that equalizes the pressure and solves the problem. Turn off kitchen and bath vent/fan units.

Before you light the fire, do you twist up a piece of newspaper and light it and stick it upwards toward the flue to establish draft? Then, strike the match to see if the chimney has a good draw and start the fire.

You indicate inserts, perhaps opening the damper more so that you get a better draw may help. Building a more active fire can often provide more draw. If smoke odor is more evident at the end of the fire as it dies down, then the house is returning to negative pressure. Negative air pressure in the home is due to lack of air. Heat rises. Positive pressure tends to be in top of house. Cold air sinks to basement where there is negative pressure.

There are chimney caps available that prevent wind entering chimney, down drafts, and back puffing. A chimney professional can advise you if chimney is properly built within specifications for proper draw. For instance, chimney should exceed 3' above roofline and 2' higher than any obstruction (such as another roof line) within 10'. Chimney information from firewood.com

Wood stove top menu

Homes today are built tighter, so that is often a major factor in contributing to negative pressure in homes. Burning a wood fire consumes a lot of indoor air. So, the fire will attempt to draw air anywhere it can such as around windows, doors. If fireplace does not get enough air, then the negative pressure will draw the smoke to the lowest level. If there is a second flue, smoke will cross draft to the second flue, such as the one for your insert, and back into the home at the lowest point. Handouts - Why burn outside air?
 
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Old 12-11-08, 08:27 AM
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I used to have a similar problem at my house. The problem was that the separate flues shared a single, multi-flue chimney cap. The smoke from the fireplace would spread out and "hang" under the common chimney cap. As it cooled, it would sink down through the furnace flue into the basement. I verified this by turning off the basement lights and using a strong flashlight to look for smoke. With the flashlight, I could see the smoke coming out through the barometric damper on the furnace.

I had intended to create a sheetmetal baffle between the flues inside the common chimney cap. However, I ended up relining both flues (for other reasons) and now have individual caps. The problem has gone away.

If you have a multi-flue cap, or if the two flue exits are very close to each other, this may be part of your problem. If so, you need to find a way to isolate the flues more. Maybe separate caps and/or some sort of veritcal baffle between the flue exits?
 
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Old 06-24-09, 06:37 PM
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smoke smell from fireplace when air condition is on

have alot of smoke smell coming thru register when a.c. is on. have 2 fireplaces main level and basement insert. the basement smells like crazy and drawing to the furnace and blowing thru the house. this is a 90 unit that has an inlet and exhaust outlet/ checked to see if pluged, not, opened windows, closed dampers, glass doors, and still drawing from the basement fireplace, it is in the high 80's and dry outside. A.C. seems to be working fine but drawing the fireplace like crazy, lived in the house 11 yrs never had it this bad.
 
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Old 06-25-09, 07:55 AM
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My thoughts

Originally Posted by huntnut4ever View Post
have alot of smoke smell coming thru register when a.c. is on. have 2 fireplaces main level and basement insert. the basement smells like crazy and drawing to the furnace and blowing thru the house. this is a 90 unit that has an inlet and exhaust outlet/ checked to see if pluged, not, opened windows, closed dampers, glass doors, and still drawing from the basement fireplace, it is in the high 80's and dry outside. A.C. seems to be working fine but drawing the fireplace like crazy, lived in the house 11 yrs never had it this bad.
If cooling coil is in the basement, they often cut a large return vent in the plenum to keep the coil from getting iced up. If you have dampened down the supply vents in the basement, then there can be a negative pressure caused by the oversized return. Have you recently replaced or sealed the interior door to the basement? I would try opening the interior basement door to see if that helps. You should be able to use a draft detector (eg burning punk stick) to see if draft through stove is decreased when someone opens the door.

If this is the case, then you will have to either 1) increase the supply vents in the basement, or 2) vent the interior basement door to decrease the negative pressure. Remember, beyond the smell, you are drawing in hot, outside air that adds a load to your AC unit.
 
 

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