I smell smoke. But why?

[walkingbaboon]

When we first lit a fire in our fireplace, we smelled smoke on our second floor and in our basement. There were a few cracks in the mortar in the back of the fireplace and as a result we suspected cracks might be elsewhere too. For this reason we thought we'd need a chimney liner (and have been thinking about installing an insert for our fireplace).

We just met with a reputable and highly recommended chimney and masonry contractor who said that he doubted there were cracks but that it was more likely that smoke was being drawn down the (unused) furnace flue, and suggested plugging the unused flue with insulation (or something else) from the top. We have a chimney cap so hopefully it wouldn't get wet. This is obviously a cheaper solution than the liner. But does his explanation (and his solution) makes sense?

Also, should (or can) we stop the draw of air down the other chimney by plugging it at the bottom near the ash drop rather than the top?

Potentially relevant details:
House was built in 1917, 3 stories tall, clay tile with brick exterior, plaster on the inside of the clay tile (no insulation, no wall studs on the exterior walls). The only fireplace is on the first floor. Chimney is brick lined with clay tile (straight shot up, no bends). Ashdrop is in the basement. Furnace was upgraded before we bought and is direct vent (so no longer uses the chimney). HW heater vents in a different chimney. Top of the chimney was repointed recently, and has a cap.

I don't know what kind of furnace the house used to have (From the age, I suspect some sort of coal burner). The basement wall that has the ash drop is drywalled so I can't see where the older furnace opening is/was. Would the "furnace" chimney have been connected to the same ash drop as the fireplace?

White vertical whitish lines in the back of the fireplace in this image were filled in with masonry "caulk" for fireplaces.

 

[DAKSY]

First of all, did the contractor actually look down the chimney flues with a camera? That's where you probably want to start. Get a thorough inspection of your system. It could be that there is some communication between the chimney flues. Secondly, I would definitely block the hole in the wall where the last furnace vented. If you're burning wood upstairs & the basement smells like smoke, then the unused flue is drawing replacement air in through the unused flue. The smell of smoke on the secnd floor is worriesome & another reason to get a complete chimney inspection...

 

[begreen]

+1. Also, a liner may still be advisable, especially if the flue tile is large or if there are any flaws in the clay tile. Given the age of the house and chimeny I would plan on a full liner. The insert will function better and it will be much easier to clean. If there is an adjacent flue at the chimney top, the new liner should terminate about a foot above the other.

 

[clemsonfor]

Yea i would run a liner when you get a stove. Yes smoke will draw back down the flues. U can use insulation but a better seal would be to get some thin galvanized metal and then use some RTV silicone and silicone it down to the top of the unused tile.

 

[My Oslo heats my home]

I have heard of the downdraft of one flue next to another at the top of a stack. You hear alot of that with the British rowhouses that have multiple chimneys coming up together. I like the idea of the SS liner being installed and the unused chimney being plugged at the top (not permanently) to eliminate the draft issues with the second chimney.