Smoking chimney and smoking fireplaces part 6: fireplace smoke enters rooms

It is one of the most valued features in our homes. And all too often, the fireplace is labeled "non-working" and sits unused, because the homeowner doesn't know what to do about a smoking problem. Here I will show how most smoking problems can be handled relatively easily, with little or no expense. We'll cover:

If you're saying, "my fireplace smokes", here's a trick for monitoring smoky fireplaces: If you can't see the smoke spilling from the fireplace, shine a flashlight across the fireplace opening. The light reflecting off the smoke particles will make it easy to see. 

Fireplace causes smoke to enter other rooms - smoking chimneys

You operate the fireplace, and smoke enters the basement below, or some other room in the house. Sounds like a strange problem, doesn't it? But it is fairly common. 

Some non-chimney-related possible causes are:

  • Open windows, allowing smoke outside the house to come in. Sounds silly, but this happens more often than you might think.
  • Fans or air exchange systems drawing smoke back into the house.
  • Air currents in the house drawing smoke from the room where the fireplace is located. 

If none of these seem to be the case, focus on the smoking chimney related possibilities: 

Downdraft in second flue

Some chimneys contain more than one vertical passageway (flue). Often, a furnace or another fireplace or stove vents through the second flue. But if either (a) there is an unused second flue, or (b) the appliance it serves is not currently being used, then the unused flue, being cold, sometimes draws cold air down into the room where the chimney connection to the second flue is located. 

Cold air sinking down this second flue can bring smoke from the fireplace with it. So the smoke is literally traveling up one flue and down the next. Check to see if the room where the smoke is found contains an opening into a second flue (or an appliance, like a stove or furnace connected to a second flue). 

Note: Sometimes old openings into chimney flues are covered with a metal "pie plate" on the wall. These are likely spots for smoke to enter, as "pie plate" covers are not air tight.

If you don't plan to use that flue or appliance, have a chimney professional seal the flue. This can be done either at the top of the chimney or where the unused appliance connects. Your chimney professional will advise you on the best way to do it. 

If the second flue serves a fireplace that you sometimes use, have your chimney professional install a top-sealing damper on the second fireplace. This is a damper at the top of the fireplace flue, which you operate by means of a cable connected to a handle in the fireplace. It seals the second fireplace from the top, much more tightly than a standard throat damper (the cast-iron kind, installed just above the fireplace opening). 

Of course, you have to open it when you use the second fireplace, but when you are using only the primary fireplace, keep it shut and no smoke will be drawn down to that room. And for those times when you want to use both fireplaces, a cold flue won't be a problem. 

If the second flue serves a furnace, a wood stove, or some other appliance that you use, consult your chimney professional, as this can get sticky. Usually, the solution will be modifications to the chimney (such as adding height), re-lining with an insulated lining system, or some kind of chimney cap. A comprehensive look at the chimney structure by an expert will be necessary to make an accurate recommendation. 

Breaks between adjacent liners

Cross your fingers and hope this isn't the problem. If you have more than one flue in the chimney, you should have a liner in each flue. If there are breaks in the linings, smoke could be crossing over to one of the adjacent flues. A cross-flue problem like this can result in smoke leaking into the home through a chimney-connected appliance in another room. 

The best way to build a masonry chimney is to separate each flue with a solid brick partition (called a wythe). But in some regions, a wythe is not required by code. And even in areas where it is required, some chimneys are not actually built with a wythe between the flues. 

If the flue liners are broken, or shift, creating gaps, and no wythe is present, smoke can cross over into an adjacent flue. If that flue is cold, the smoke might be drawn back into the house. 

The solution is to re-line the chimney – not just to solve the cross-flue problem, but because a damaged flue liner is a serious fire hazard. If you use both flues, you need two new liners. Consult a chimney professional, and request a thorough check of the flue liners to determine if they are damaged and in need of replacement. 

Chimney cap too short

Chimney liners often extend a few inches above the top, or crown of the chimney. This is deliberate, as it helps keep water on the chimney crown from funneling down into the flues. But if you have a chimney cap (which you should) it is important to have enough space between the tops of the liner tiles and the cap. If the chimney cap is installed with too little space between the cap and the liners, smoke could back up into the house. 

Check the space between your cap and the tops of the flue liners. Use binoculars if you can't tell, or ask your chimney professional to check it next time you have the chimney cleaned. Five inches or so is fine for a normal-sized cap, and often slightly less than that is adequate. But if the cap's only a couple of inches above the tops of the flue liners, either (a) have the liners cut down, but not lower than your state and local codes require, or (b) install a taller cap. 

And if the cap's unusually large – for example, if the chimney top is four feet wide and six feet long, and you have a full- sized cap on it, with the flues located under the center of the cap – then you might need a little extra space between the tops of the flue liners and the cap, since the cap could act like a baffle, retarding the flow of flue gasses. 

If you think the cap is too low, but you are not sure, try removing it temporarily, and try the fireplace without it, before you start changing things. But a cap's important, so make necessary corrections and re-install it promptly.

 

Smoke Signals: Have a question about your chimney?