Concerned about smoke and downdraft when not burning

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New Member
Apr 17, 2024
I'm about to pull the trigger on installing a wood stove insert into our masonry chimney but I'm concerned about downdraft and a smell when the stove is not burning. I've seen a few other posts that hint at this potentially being an issue. Details are:

- 100+ year old 2 story house, definitely not airtight
- There is a noticeable draft in the chimney as is (we have it "closed off" with fireplace doors) but it is quite noticeable. The bricks on the hearth are noticeably cold in the winter.
- It's an exterior chimney on a sheltered north/east facing wall, unlined but would install an insulated liner + insulation above the insert.
- The stove is for ambiance and to supplement the current heat system so I anticipate using it mostly in the evenings and probably not every night over the winter. Not planning on burning around the clock.

Is this going to be a likely issue? The last thing I want is to spend the money on the insert and regret it because I've added smoke fumes in the house.

Install the insulated liner and a block off plate should keep those issues from happening
Agreed, an insulated block-off plate will help reduce heat loss so that the insert can perform better. If there is room behind the insert then some insulation behind it will also help.

If there is no downdraft and smell now, then it probably won't be an issue.
I think the OP meant (with "draft") that there is cold air coming down the chimney now - leading to a cold hearth.

The block off plate will prevent cold air from sinking down outside the liner. But there can still be air coming down inside the liner. That would then go through the insert into the room. However, it's unlikely that will be more than what it is now.

The insert will improve the energy efficiency of the home, even when not burning it, as it will leak less than the fireplace does now.

If the chimney is 2 stories tall, the height should be enough.
Note that any fans in the home (kitchen or bathroom exhaust) that are on might suck air in through the flue (now and later).

If you're going to be an evening/weekend burner, I would get a non-cat insert.
And make sure you have working CO and smoke detectors on each floor and in the room with the fireplace.
Finally, note that (modern) inerts need wood to be drier than what one can burn in a fireplace. So I suggest to get firewood now, stack it off the ground and top covered. Buying seasoned or kiln-dried firewood often results in disappointment when burning a modern insert as it's often not dry enough despite the sellers' claims.
Amazing - thanks everyone. The chimney has been inspected - it's in good shape. To clarify - currently there is a noticeable 'down draft' in the fireplace. I added some weather stripping between the glass fireplace doors and the brick to help but it's pretty noticeable anyway (current damper is totally shot). The bricks are cold - not sure if that's from the draft or the chimney just generally being a cold sink. We're in coastal New England so temps below 20 degrees are common.

The shop I'm talking to is hesitant about installing a block off plate - they said the plate can delay noticing water coming in the chimney and they recommend just stuffing the area around the liner with mineral wool.

The point about added smell being unlikely if there's no smell now is reassuring and makes total sense.

And I believe we're looking at an RSF focus 3600 insert - we need a flush mount and I didn't want to worry about a cat.
Rockwool will still be letting air through. Air sealing (metal plate+silicone bead), plus rockwool insulation is the best.

My opinion is that that if they don't have trust in their ability to make the chimney closed free from water intrusion, you better find another shop...
The shop I'm talking to is hesitant about installing a block off plate - they said the plate can delay noticing water coming in the chimney and they recommend just stuffing the area around the liner with mineral wool.
That's a strong argument for a proper, well sealed top cap, but not to skip the blockoff plate.

If there is currently some downdraft then there may be negative pressure in the room. This can be caused by air leaks in the second story. Some typical causes are a leaky attic door or hatch, an open whole house vent in the ceiling or leaky windows.

Other causes can be exhaust fans in the kitchen or bath, a dryer, radon fan, etc.
I'll have to ask them about the block off plate again. Perhaps something I'll make ahead of time and ask them to install with the stove.

Unfortunately it's just a leaky old house. We've sealed as best we could around doors, windows, etc. We'll insulate and seal the attic someday but between having to update the wiring and then seal and add insulation its crazy expensive.
Sealing the attic is not expensive - if you do it yourself.
I did. Bought 20 cans of polyurethane spray foam, and a few tubes of silicone. The latter for any electrical box or penetration (spray foam is flammable). The former at all sides of top plates of internal and external walls.
You have to pull up the existing insulation, then work on the seams and electrical penetrations. Then put the insulation back.

(I also spent $1000 on unfaced R38 batts that I put on top of, and 90 deg rotated from the existing faced R19 insulation that was between the joists. That gave me R57 and a sealed attic.)

The attic hatch can be closed quite well with a $50-$100 big box store thing, or make something yourself as I did with 2 latches on the attic hatch, a strip of felt on the sides of the attic hatch where it meets its counter part at closing, and then pink foam boards installed on a ledge (and I glued insulation batts on top of that foam board).
The felt and latches seals it, and the foam board + batts insulate it.

All that for less than $200 in sealing and $1000 in insulation. And a total of 6 weekends in the attic.

Together this at least halved my heating needs. I think it was 2/3rd less.

Anyway, a home will function as a chimney just like the chimney does; air moves up. If one prevents air from being able to get out in the top levels, less will go up, and the pressure at lower levels will not be as negative, decreasing air entering through the chimney.

Another thing to look at is sealing all electrical outlets and switchs. Not only on external walls, but also internal ones (as any warm air intrusion there can easily move either to the attic if not sealed as described above, or to the side walls of the home and leak out at rim joists). Use silicone to close the holes where wires enter the boxes, and use a $2 foam template from the big box store under the "lid" of the boxes.

This sounds all like a lot of work, but if you spend only the weekends for 2 months and get this all done, you'll likely save at least 50% on your heating bill. I did in a 1978 home.
I wish it were that easy but the electrical needs to be updated for most of the second floor which is a large part of the cost. I'm not trying to put all that work and insulation in around old wiring.
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