Smoke Up One Flue and Down The Other -- Help!

kreinhardt

New Member
Oct 13, 2019
8
Cornwall, CT
Hi,

First time poster, and also first-time homeowner (...if I had only known!)

Anyways -- I have a dual-flue chimney that supports an upstairs fireplace, as well as a basement wood stove. Facing the chimney indoors, the upstairs fireplace is the right flue, and the basement stove is the left flue (see pics for context, which show my one-night temporary fix to block off the downdraft with aluminum tape...no more fires until I properly address the issue!).

Having looked both upward and downward, I'm 95% certain that each is independent of the other the length of the chimney, and for what it's worth, the basement is insulated.

I've come to discover that when I have a fire upstairs, smoke is going up that flue and down the other, causing the basement wood stove to emit smoke. I somewhat understand this is because there's a negative draw down to the basement, and that the stove flue stoppers and damper aren't fully sealing. I hope to fix that by to the best of my ability by disassembling the stove-to-chimney flue pipe and ensure that the inner damper can rotate to full-close, and to also redo fire ropes on flue collar & stove doors. I'm not sure if that will fix the issue, or if I there are other forces I should consider?

Could someone please speculate on the dynamics of my current issue / setup? And also give some council / guidance on how to best address?

Any council / guidance, preferably qualified :), would be MUCH appreciated!

- New Home Owner (aka, Kevin)
 

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EatenByLimestone

Minister of Fire
Jul 12, 2006
7,329
Schenectady, NY
What does the top of the chimney look like?
 

kreinhardt

New Member
Oct 13, 2019
8
Cornwall, CT
What does the top of the chimney look like?
Thanks for the response, Matt.

Here's an likely unhelpful picture of the chimney from the outside (won't be able to get on top until later today when I have a ladder spotter). Having been up there before, there are two distinct terracotta channels for each flue at the top, but that said, it doesn't truly mean that they're independent of one another (could be common below the top chambers).

Kevin
 

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fire_man

Minister of Fire
Feb 6, 2009
2,365
North Eastern MA
Can you put a 3' temporary extension on your fireplace flue to see if that fixes the problem?
 

kreinhardt

New Member
Oct 13, 2019
8
Cornwall, CT
That's a good thought, and thinking about this more...would an alternative to an extension be a top-mounted damper? That'd surely have to seal fully to prevent any drawdown, right? I think it would allow me to keep the current common-level flue setup w/o extending one around and above the chimney cap.

Definitely check my thoughts on the top-mounted damper vs. extension...my knowledge-base is beyond novice here :)
 

EatenByLimestone

Minister of Fire
Jul 12, 2006
7,329
Schenectady, NY
What happens if you open a basement window when you run the upstairs fireplace? In a tight house, I can see a fireplace pulling so much air that it can only be made up by pulling air down the other flue.
 

jetsam

Minister of Fire
Dec 12, 2015
4,720
Long Island, NY
youtu.be
Make the upstairs flue 2-3' taller with a piece of stovepipe, and add an air intake for the basement stove. You probably can't do a proper OAK, but you can add a PVC pipe with a valve on it and a warm-air trap outside to admit outside air near the stove.
 
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kreinhardt

New Member
Oct 13, 2019
8
Cornwall, CT
Make the upstairs flue 2-3' taller with a piece of stovepipe, and add an air intake for the basement stove. You probably can't do a proper OAK, but you can add a PVC pipe with a valve on it and a warm-air trap outside to admit outside air near the stove.
Flue extension is doable (I'd rather add an upper damper, if that's possible), but the downstairs OAK might be challenging. There's an OAK on the upstairs fireplace, but putting a proper one in the basement for the stove would take some doing (is adding one to the chimney post-construction even possible? I'd obviously have to do some serious masonry drilling). See pics of current OAK on the upstairs fireplace.

I'm not sure I follow your PVC pipe / valve suggestion (where would this be connected to?).
 

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begreen

Mooderator
Staff member
Nov 18, 2005
82,958
South Puget Sound, WA

jetsam

Minister of Fire
Dec 12, 2015
4,720
Long Island, NY
youtu.be
You shouldn't consider a basement OAK unless it's a walk-in basement. The outside air has to stay lower than the firebox at all points, which is not possible in most basements.

The PVC pipe I suggested would not connect to anything- it would only admit outside air into the room. It's a work-around for people who can't have an OAK for one reason or another.
 

kreinhardt

New Member
Oct 13, 2019
8
Cornwall, CT
You shouldn't consider a basement OAK unless it's a walk-in basement. The outside air has to stay lower than the firebox at all points, which is not possible in most basements.

The PVC pipe I suggested would not connect to anything- it would only admit outside air into the room. It's a work-around for people who can't have an OAK for one reason or another.
Okay, well it is a walk-out basement (two large french doors, as well as two windows). To that point, thought, I'm not totally sure that the outside-to-inside airflow via an OAK (or PVC workaround) will bring a whole lot of benefit, as even when I have one of the french doors totally open (did this to help clear out the smoke), the downstairs wood stove flue is still drawing down smoke from the upstairs fireplace flue.

I stopped into a Fireplace / Hearth store, and I got suggestions from raising the bluestone chimney cap ~12" (currently 8" raise), to taking the cap off and putting a staggered extension on one / both of the fluepipes (a suggestion that came up earlier, and we seem to be headed that way). I also got a comment of "I don't think you're going to be able to solve that problem", to which I replied "so you're saying everyone in history who has ever had a dual-flue chimney has / always will have negative draw? And, therefore, I have an unusable chimney? (Maybe my I can't see through my novice understanding of the dynamics at play, but I find it difficult to believe that it's "unsolveable".

Hmmmmm. Will try having a fire in the woodstove tonight to see if there's the same drawdown into the upstairs fireplace (haven't experimented with this yet). If not, then the main issue is the downstairs flue, which I guess I have a few options to explore (*cracked* window, flue extension).

Who knew home ownership is such a journey?!
 

begreen

Mooderator
Staff member
Nov 18, 2005
82,958
South Puget Sound, WA
It's a common enough problem that there are products made to solve it. Be sure they extend the upper fireplace flue and not the basement flue.

This article should be helpful in understanding negative pressure on the lower floor of a house.
 
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brenndatomu

Minister of Fire
Aug 21, 2013
5,062
NE Ohio
From your outside chimney pic it looks like there are two separate flues that discharge into one big area created by that stone cap...if that cap could be cut in half and the one side raised (with a divider in between the two flues) I bet that would do a lot to remedy the situation...with it the way it is now its really just inviting this problem to happen!
 

jetsam

Minister of Fire
Dec 12, 2015
4,720
Long Island, NY
youtu.be
aeven when I have one of the french doors totally open (did this to help clear out the smoke), the downstairs wood stove flue is still drawing down smoke from the upstairs fireplace flue.
You will probably also have a heck of a time starting a fire downstairs in mild weather.

I would personally see that as a hazardous situation. Probably get rid of the stone cap and extend the downstairs flue the minimum needed to get a cap on it, then extend the upstairs flue as much as is practical. Or maybe just drill a hole in the cap for the one flue, but big core bits are hundreds of dollars.

Definitely preheat that flue and test the draft before trying to light a fire there. (Run the torch in the stove for a couple minutes to warm the flue, then put a lit match or candle in front of the open stove door. Flame/smoke pulls into the stove, light the fire. Flame/smoke blows back at you, do not light the fire.)

I've heard of people using electric heat guns for this purpose too (they sell them for stripping paint and thawing pipes).

If that fireplace is an unlined open fireplace, not using it may solve your problem by itself. Those things blow a tremendous volume of air out of your house.
 
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brenndatomu

Minister of Fire
Aug 21, 2013
5,062
NE Ohio
I've heard of people using electric heat guns for this purpose too (they sell them for stripping paint and thawing pipes).
Don't forget the lowly hair dryer...that's the trick I taught my sister to use to help with the downdrafts she commonly deals with in milder winter weather...works great!
 
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SpaceBus

Minister of Fire
Nov 18, 2018
4,329
Downeast Maine
You will probably also have a heck of a time starting a fire downstairs in mild weather.

I would personally see that as a hazardous situation. Probably get rid of the stone cap and extend the downstairs flue the minimum needed to get a cap on it, then extend the upstairs flue as much as is practical. Or maybe just drill a hole in the cap for the one flue, but big core bits are hundreds of dollars.

Definitely preheat that flue and test the draft before trying to light a fire there. (Run the torch in the stove for a couple minutes to warm the flue, then put a lit match or candle in front of the open stove door. Flame/smoke pulls into the stove, light the fire. Flame/smoke blows back at you, do not light the fire.)

I've heard of people using electric heat guns for this purpose too (they sell them for stripping paint and thawing pipes).

If that fireplace is an unlined open fireplace, not using it may solve your problem by itself. Those things blow a tremendous volume of air out of your house.
Do you think the fireplace would pull the smoke into the house if he lights the stove?

To the OP: Did the fireplace show any signs of use prior to you using it? What about the basement stove?
 
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kreinhardt

New Member
Oct 13, 2019
8
Cornwall, CT
Do you think the fireplace would pull the smoke into the house if he lights the stove?

To the OP: Did the fireplace show any signs of use prior to you using it? What about the basement stove?
Yes, both have signs of significant use, albeit being well kept / cleaned.

Speaking to my neighbor, he said the the former owner (who was a real "character", to say the least) always had this problem....May explain why he was such a character. Regardless, I need to test the stove to see if there's a draw into the fireplace (will do another evening this week, as the flue collar is disassembled and I can't take on reassembly this evening).

A big thanks to ALL who posted their insights / ideas on how to solve my connundrum. I'm also going to call a few different fireplace guys tomorrow and see if I can get them to swing by and give separate diagnosis / quotes. I'm not wed to having the chimney cap and would willingly get rid of it if I need to do one / two extensions (sounding like the best / only option)...however, I AM we to the idea of having two functional fire sources! That's one of the many things that gives this house appeal!

I will persevere, and update you all on my progress. Stay tunded!
 

brenndatomu

Minister of Fire
Aug 21, 2013
5,062
NE Ohio
I think, could be wrong, but standard/best practice when having multiple flues next to each other is to have them each separated by a foot or so in height...one thing I wonder about is if the height is supposed to increase or decrease if going with the direction of prevailing winds?
 

SpaceBus

Minister of Fire
Nov 18, 2018
4,329
Downeast Maine
Yes, both have signs of significant use, albeit being well kept / cleaned.

Speaking to my neighbor, he said the the former owner (who was a real "character", to say the least) always had this problem....May explain why he was such a character. Regardless, I need to test the stove to see if there's a draw into the fireplace (will do another evening this week, as the flue collar is disassembled and I can't take on reassembly this evening).

A big thanks to ALL who posted their insights / ideas on how to solve my connundrum. I'm also going to call a few different fireplace guys tomorrow and see if I can get them to swing by and give separate diagnosis / quotes. I'm not wed to having the chimney cap and would willingly get rid of it if I need to do one / two extensions (sounding like the best / only option)...however, I AM we to the idea of having two functional fire sources! That's one of the many things that gives this house appeal!

I will persevere, and update you all on my progress. Stay tunded!
Your fireplace is mostly a decor item. When burning a fire it will actually cool the house down since all your heat goes out the chimney. There are high efficiency fireplaces, but they are quite expensive to purchase and install. The wood stove in the basement would be the primary heater. You should post some photos of the stove install. A good chimney sweep will also be able to help you out, the fireplace guys are trying to sell fireplaces and accessories.
 
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kreinhardt

New Member
Oct 13, 2019
8
Cornwall, CT
Sorry, All - - I just realized that in my original post I didn't include a picture of the basement stove (is now updated / shown).

Please feel free to chime back in if the calculus has changed with the new pic.

Time for bed!
 

kreinhardt

New Member
Oct 13, 2019
8
Cornwall, CT
Your fireplace is mostly a decor item. When burning a fire it will actually cool the house down since all your heat goes out the chimney. There are high efficiency fireplaces, but they are quite expensive to purchase and install. The wood stove in the basement would be the primary heater. You should post some photos of the stove install. A good chimney sweep will also be able to help you out, the fireplace guys are trying to sell fireplaces and accessories.
Thanks for the insight :) . I've updated the OP with pictures of the stove install. And yes, the stove in the basement is the primary heater, with the fireplace being decor / ambiance (IMO, running it for special occasions makes the heat / money it expends well worth it!).

And 10-4 on the Chimney Sweep vs. fireplace guys; they felt "salesy" from the get-go.
 

jetsam

Minister of Fire
Dec 12, 2015
4,720
Long Island, NY
youtu.be
I don't know what's going on in that stove's flue pipe, but it is nothin' good. (Maybe a black garbage bag stuffed in as a temporary air block?)

Fireplace-wise, generally the area of the flue is 0.1 the area of the fireplace opening. Stoves of a size that people put in houses generally operate on a 6" pipe, or an 8" pipe for the larger ones.

So a stove with the door open has 28 square inches open to the sky, whooshing air out of your house. (Once you close the door, the rate of exhaust gets much lower, down to very little if you have a stove with good air control doing a low burn.)

A fireplace with a 28 square inch flue (like a regular woodstove), your fireplace opening would be 16.8" x 16.8", which is smaller than any I've ever seen.

Your fireplace (at a guess) is roughly 36" x 36", which calls for a 130 square inch opening.

SO: Your fireplace's flue is probably over 4x the size of your stove's flue. The fireplace has absolutely no air control except for the damper (which, as anyone who has closed one on a burning fire will tell you, generally remains open while the fireplace is in use), and is exhausting warm air very quickly when it's not burning, and much faster than that when it is burning.

The stove not only has a much smaller flue whooshing warm air out of your house (which also sucks in the same volume of cold outside air), but it also limits how much air goes up through the flue via its air controls. (Plus it is engineered to put heat into the room, not up the flue, and modern stoves have a reburn system...)

This is why fireplaces became obsolete in the 1700s. We're still catching up with the news, I guess. (I grew up in two houses "heated" primarily with open fireplaces, and I have no idea why anyone would have decided that was a good idea in the 1800s, let alone the 1900s. At least in the 1700s they could have argued that British restrictions on American steel production and blacksmithing made the stoves too expensive.)
 

EatenByLimestone

Minister of Fire
Jul 12, 2006
7,329
Schenectady, NY
If that stove is your primary heat, I recommend upgrading it. Your going to use a lot of wood burning that.
 

begreen

Mooderator
Staff member
Nov 18, 2005
82,958
South Puget Sound, WA
A choked down Defiant is going to add to the problem if draft is weak. The stove is supposed to have an 8" flue all the way.