Why is smoke entering my home through the fireplace?

Question

I recently moved to a new home with a wood burning fireplace. I've never owned one of these before and I want to become familiar with it.

With a fire extinguisher and a pot of water ready, I placed some kindling and a dry log (that came with the house) in the fireplace, along with some clippings from a shrub and some clippings from a paper shredder. Then, I lit the fire and closed the door.

Within a few minutes, a cloud of noxious smoke wafted into the room. Not knowing what could be wrong, I drowned the fire. After this, I stepped outside and observed that there was a little bit of smoke rising from the chimney.

As someone who has never owned a fireplace before, what do I need to know to operate my fireplace safely and avoid smoke coming in my home?

Answer 1

Damper closed - most likely.

Chimney blocked - while "damper closed" is a self-correctable version of this, if the fireplace has not been inspected there may be anything from bird nests to parts of a chimney in serious disrepair blocking the flue.

SO - before you become a statistic (of the chimney fire sort) call a chimney sweep and have the flue inspected to be sure it is in safe condition to use, and find out where the damper control is (often a lever or chain hanging down in the top of the fireplace.)

Another possible problem, particularly common if the fireplace & chimney is on the outside wall of the house, would be an excessively cold flue - sometimes curable by putting newspaper up into the throat of the fireplace and lighting it (before lighting the fire), to get air moving the right direction (up and out.)

Answer 2

Chimneys have a damper, which is a flap meant to be closed when the chimney is not in use. Look up from the inside of the hearth and you'll likely see a handle or chain. Generally you cannot see the sky, even with the damper open.

If the house is new to you, but not new, have the chimney inspected, and the nice person who does the work will give you tips on fire starting. Shrub clippings are likely too fresh to burn without excessive smoke. My parents liked to start a bit of newspaper up the chimney to get the draft going, but that's purely a refinement of the technique.

When done, close the damper to prevent loss of conditioned air.

Answer 3

"Flue Blockage" is the generic answer, ranging from the sliding damper being closed to some kind of physical blockage. A fire doesn't need to be totally blocked for there to be smoke come back into the room. It is a simple case of pressure - if there's less pressure in the room than in a slightly-blocked flue you will still get smoke blow back into the room.

Two common cases not mentioned by Ecnerwal are

1. Depending on the type of your fireplace, many have a metal plate in the top of the fireplace which can be removed. This makes the hot air rise in a flattened "S" shape across the top of the fire, before it goes up the flue. If this plate has been dislodged or put back at an angle, it can impede the flow of air.
2. Your flue may be blocked with soot - loose, fluffy, sticky material from partly-burned material. This is often cleaned by professionals. I have cleaned it using a long stiff wire, the high-tensile steel wire used in farm fences. With a section about 1.5 times the height of the flue (yes, I'm talking many meters) I fed it into the flue and swirled it around in a spiral motion as I went. This approach requires being able to clearly access the bottom of the flue, which means removing a heavy plate such as described in point 1.

Cleaning soot from your flue may need to be an annual event - it depends hugely on what you burn and particularly how "green" the wood is - wood for burning should generally be seasoned by being stored for at least a year, for sap to evaporate.

Answer 4

I have a modern home that is sealed against draughts. If I light my wood burner and all the windows are closed, as the fire burns it reduces the pressure in the room. This causes the smoke to start coming back down the chimney and into the room. So a suggestion would be to ensure you have a window open before you light the fire.