Mysterious smell, common ideas checked already...

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zsoltc

New Member
Dec 5, 2021
13
SE Michigan
Hello Fellow Wood Burners,

I found this site and registered recently to try to figure out a problem I am seeing (more like smelling) the first time. Let me give you the history, what I did and checked so far.

The house is an 1987 ranch, it has its original masonry fireplace. The fireplace is located in the living room, the chimney and the fireplace is built in a way, half of it is essentially the exterior of the house (I hope I am describing it correctly, not sure about the proper term). We bought the house in 2018, the fireplace was not used since then. The fireplace has a glass door and a damper just above the firebox, which seems to seal well (inspected visually and no draft of any kind when closed). The chimney has a chimney cap.

This year we wanted our first fire so I called around to have a chimney sweep company clean the chimney/fireplace. Labor shortage etc. I was told they can come in 2 months... I took the issue in my own hands and ordered the rod-and-whip system (Gardus SootEater). I checked several reference images how a clean flue should look like. My impression was that the flue looks very clean, but I went through it with the whip anyway. I also brushed the firebox and the damper with a wire brush then cleaned the debris and the ashbox.

I have experience with terracotta stoves from my childhood so I figured this should be similar. Made a fire, lit up, it was beautiful. I could smell just a bit of smoke when the fire was lit but I was used to it from the terracotta times. The fire had a very nice shape, I would say it definitely had a good draft. The glass door was completely opened. In order to play it safe, I only had a single batch burnt, to make sure I am not doing something wrong, so the chimney / firebox / fireplace wasn't too hot I assume (not sure if this matters).

Since the evening of this first fire I can smell a smoky scent. The smell is like the smell of your clothes when you sit next to a campfire for 2 hours. It's not smoke but that smoky smell. I stuck my head in the firebox, I can' really smell anything. The damper is closed and I can feel no draft. There was some older insulation between the masonry and the door, I pulled that out and threw away, because it seemed that the top part of the door is where the smell comes from. Opened a couple of windows and now waiting whether the smell persists.

The masonry was whitewashed with standard latex paint diluted at a 1:10 ratio, there is a small portion of the masonry which is covered by the door and heat might be trapped there but I doubt it can burn the paint...

Please help investigate, I am both bothered by the smell and want to make sure it is not a health hazard, especially now with our 2month old son.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,443
central pa
Hello Fellow Wood Burners,

I found this site and registered recently to try to figure out a problem I am seeing (more like smelling) the first time. Let me give you the history, what I did and checked so far.

The house is an 1987 ranch, it has its original masonry fireplace. The fireplace is located in the living room, the chimney and the fireplace is built in a way, half of it is essentially the exterior of the house (I hope I am describing it correctly, not sure about the proper term). We bought the house in 2018, the fireplace was not used since then. The fireplace has a glass door and a damper just above the firebox, which seems to seal well (inspected visually and no draft of any kind when closed). The chimney has a chimney cap.

This year we wanted our first fire so I called around to have a chimney sweep company clean the chimney/fireplace. Labor shortage etc. I was told they can come in 2 months... I took the issue in my own hands and ordered the rod-and-whip system (Gardus SootEater). I checked several reference images how a clean flue should look like. My impression was that the flue looks very clean, but I went through it with the whip anyway. I also brushed the firebox and the damper with a wire brush then cleaned the debris and the ashbox.

I have experience with terracotta stoves from my childhood so I figured this should be similar. Made a fire, lit up, it was beautiful. I could smell just a bit of smoke when the fire was lit but I was used to it from the terracotta times. The fire had a very nice shape, I would say it definitely had a good draft. The glass door was completely opened. In order to play it safe, I only had a single batch burnt, to make sure I am not doing something wrong, so the chimney / firebox / fireplace wasn't too hot I assume (not sure if this matters).

Since the evening of this first fire I can smell a smoky scent. The smell is like the smell of your clothes when you sit next to a campfire for 2 hours. It's not smoke but that smoky smell. I stuck my head in the firebox, I can' really smell anything. The damper is closed and I can feel no draft. There was some older insulation between the masonry and the door, I pulled that out and threw away, because it seemed that the top part of the door is where the smell comes from. Opened a couple of windows and now waiting whether the smell persists.

The masonry was whitewashed with standard latex paint diluted at a 1:10 ratio, there is a small portion of the masonry which is covered by the door and heat might be trapped there but I doubt it can burn the paint...

Please help investigate, I am both bothered by the smell and want to make sure it is not a health hazard, especially now with our 2month old son.
You probably have a reversed draft when the fireplace is not in use pulling smell down the chimney
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,443
central pa
Can that be the case though? The damper is closed and we never had this smell before... How can this be triggered by a fire?
Yes the damper is far from air tight. And with the fire you warmed things up made new deposits etc.
 

zsoltc

New Member
Dec 5, 2021
13
SE Michigan
Yes the damper is far from air tight. And with the fire you warmed things up made new deposits etc.
How can I prove it? If yes, what is causing it? The house is single story I, have no radon system, bathroom fans are not usually running as I have windows in the bathrooms...
 

EatenByLimestone

Minister of Fire
Hold a candle by the damper. Watch the flame. I suppose insense or similar would work too.
 

EbS-P

Minister of Fire
Jan 19, 2019
2,413
SE North Carolina
Our fireplace had that smell. Cleaning all the ash out helped some. It would come back the first warm / real hot week of the season. We stopped burning. Is was just to sensitive to the smoke. We installed a wood stove/insert with insulated liner now no more smell ever.

Might try a hotter fire with really dry wood. Or bio bricks.
 

FPX Dude

Feeling the Heat
Oct 4, 2007
415
Sacramento, CA
Stuff a towel or something in there, just remember to remove when lighting again. I put a little tag on mine hanging down so I can see it to help remind me.
 
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zsoltc

New Member
Dec 5, 2021
13
SE Michigan
Hold a candle by the damper. Watch the flame. I suppose insense or similar would work too.
I tried with an incense stick. There is a very minor draft with the damper closed but still in the right direction, i.e out the chimney. Tested both with furnace on and off (forced air). I am pretty confident there is no down draft...
 

zsoltc

New Member
Dec 5, 2021
13
SE Michigan
Our fireplace had that smell. Cleaning all the ash out helped some. It would come back the first warm / real hot week of the season. We stopped burning. Is was just to sensitive to the smoke. We installed a wood stove/insert with insulated liner now no more smell ever.

Might try a hotter fire with really dry wood. Or bio bricks.
I will definitely try some other wood. This was some firewood I kept from a silver maple we had to cut down in our backyard.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,443
central pa
This would help in case of a down draft I assume, which I think I have no issues with...
You had no issue at that particular time. Outside temp barometric pressure wind etc will all Chang that.
 

zsoltc

New Member
Dec 5, 2021
13
SE Michigan
You had no issue at that particular time. Outside temp barometric pressure wind etc will all Chang that.
That's fair but I am focusing now on yesterday evening's effects. Day and night time temperatures were between 30-40F, significantly lower than the inside temperature. My understanding of the stack effect is that during winter, this would cause warm air escaping through the chimney. During summer, it is the other way round (warmer air tries to sink in the colder rooms of the house through the chimney) and that's why several other people reported smoky smell during the cooling season.
Am I missing something?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,443
central pa
That's fair but I am focusing now on yesterday evening's effects. Day and night time temperatures were between 30-40F, significantly lower than the inside temperature. My understanding of the stack effect is that during winter, this would cause warm air escaping through the chimney. During summer, it is the other way round (warmer air tries to sink in the colder rooms of the house through the chimney) and that's why several other people reported smoky smell during the cooling season.
Am I missing something?
Unless the chimney is cooled down in which case that cold air will drop down.
 

zsoltc

New Member
Dec 5, 2021
13
SE Michigan
Unless the chimney is cooled down in which case that cold air will drop down.
I really appreciate the time and effort to try to help me, but I'm not sure I am following you.
In one of the previous comments you mentioned that outside temperature, pressure and wind may affect the draft direction, now we add the chimney temperature.
These two days, the variation in outside temperature and humidity was not significant, less than 10F between day and night. There was no rain or any other significant weather change either.
Yesterday the chimney was still relatively warm from the fire, I assume it cooled down this morning and that's when I did the draft test. So almost the same outside conditions, cooled down chimney and the draft was still upwards.

This is what I wrote in a previous comment:
I tried with an incense stick. There is a very minor draft with the damper closed but still in the right direction, i.e out the chimney.

I should have added that, with the damper opened, it was a strong upwards draft, I did not even need the incense stick, I was able to feel it with my hand.
I am not saying downwards draft does not exist. I am saying that since the issue appeared, it is almost the same inside and outside condition and I see no down draft, which makes me believe it is not a factor in the smoky smell.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,443
central pa
I really appreciate the time and effort to try to help me, but I'm not sure I am following you.
In one of the previous comments you mentioned that outside temperature, pressure and wind may affect the draft direction, now we add the chimney temperature.
These two days, the variation in outside temperature and humidity was not significant, less than 10F between day and night. There was no rain or any other significant weather change either.
Yesterday the chimney was still relatively warm from the fire, I assume it cooled down this morning and that's when I did the draft test. So almost the same outside conditions, cooled down chimney and the draft was still upwards.

This is what I wrote in a previous comment:
I tried with an incense stick. There is a very minor draft with the damper closed but still in the right direction, i.e out the chimney.

I should have added that, with the damper opened, it was a strong upwards draft, I did not even need the incense stick, I was able to feel it with my hand.
I am not saying downwards draft does not exist. I am saying that since the issue appeared, it is almost the same inside and outside condition and I see no down draft, which makes me believe it is not a factor in the smoky smell.
Fair enough.
 

zsoltc

New Member
Dec 5, 2021
13
SE Michigan
Coming back to the other two suspects: what wood is good or not good to be put in a fireplace? The wood I used did sit outside for a winter, then I managed to move it in a shed and let it dry out for another year. Can the wood decay in a way it smells stronger/does not burn well?
The other thing is the insulation around the door, is that necessary? I saw fireplaces which were completely open, only a mobile spark screen in front of the firebox. How critical is that insulation, should it be "airtight" when stuffed between the masonry and the door?
 

NorMi

Member
Nov 18, 2021
110
Northern LP, MI
Can that be the case though? The damper is closed and we never had this smell before... How can this be triggered by a fire?
Fresh deposits as was mentioned. How can the smell of smoke be triggered by a recent fire? Honestly...
How can I prove it? If yes, what is causing it? The house is single story I, have no radon system, bathroom fans are not usually running as I have windows in the bathrooms...
You can smell the smoke - there, your nose proved it. There's a few things that can cause the smell of smoke in the living space:
  • The fact that a fire was recently ignited inside the living space.
  • Negative pressure potentials, such as:
    • Opening or closing a door
    • Opening or closing a window
    • A slight breeze of any wind movement greater than "0"
    • Opening or closing an attached garage door
    • Any imperfect seal on any door, window, attic access, or other opening on the house
    • The aforementioned fans, bathroom, range hood, etc, which need not be operating to generate pressure potentials
    • A vented combustion appliance running, like a furnace, hot water heater, dryer
    • Air literally passing through the walls of the house, since it's a house and not a submarine or spaceship.
That's fair but I am focusing now on yesterday evening's effects. Day and night time temperatures were between 30-40F, significantly lower than the inside temperature. My understanding of the stack effect is that during winter, this would cause warm air escaping through the chimney. During summer, it is the other way round (warmer air tries to sink in the colder rooms of the house through the chimney) and that's why several other people reported smoky smell during the cooling season.
Am I missing something?
Yes, I would say you are missing something, but it's subtle. You've read about the stack effect, a very real thing. When the chimney is "cold", i.e. no active fire within the past hour +/- the temperature differential is very small On a single story house, the vertical pressure differential is small. When the air outside is not very cold, like 30-40F ,the pressure differential is *very* small. So the mass of air from a stack effect is going to move quite slowly. When you close the doors and damper, they are not air tight, but they prevent most of the mass of air from moving. Without mass moving, the stack effect is almost completely gone - without unrestricted openings, the flow rate is much too small to make any real stack effect happen, and without mass movement/flow, there is almost no inertia in the system to resist any negative pressure potential causing inversion of (very slow and minor) flow. F=MA. Now, a gnat's fart worth of negative pressure potential can suck the fresh deposit stink right into the living space. Since it stinks a lot, a little stink goes a long way.

Coming back to the other two suspects: what wood is good or not good to be put in a fireplace? The wood I used did sit outside for a winter, then I managed to move it in a shed and let it dry out for another year. Can the wood decay in a way it smells stronger/does not burn well?
The other thing is the insulation around the door, is that necessary? I saw fireplaces which were completely open, only a mobile spark screen in front of the firebox. How critical is that insulation, should it be "airtight" when stuffed between the masonry and the door?
The perimeter insulation increases the resistance of the total system and slows the heat transfer from the house to the uninsulated masonry chimney system. It is not airtight, but it's more air resistant when the insulation is installed. The seals on your fireplace will never be fully airtight, nor fully stink proof. Only burn dry, seasoned wood in your fireplace, of course. Wood sitting outside should be covered on the top, or in a shed, good good. The wood burned well, most likely. The chimney is very heavy and massive, and the walls of the chimney are cold. Smoke condenses on any surface <300 degrees in its path and leaves a stinky moist coating. It takes a long time to get a multi-ton chimney to >300F inside. Every time you start a fire on a cold chimney, you create a new, very nasty layer of moist stink. Fresh moist stink is very stinky. A single, short fire probably never gets hot enough to dry all the newest stink juice out, since the whole chimney from top to bottom never reaches that magic temperature, which then makes the stink more stinky as well, since it's not been dried out fully, but still nice and fresh and moist. The situation stinks, quite honestly.
 
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zsoltc

New Member
Dec 5, 2021
13
SE Michigan
NorMi, thanks for your detailed answer, unfortunately, I am not sure whether there was some sarcasm (which I honestly don't appreciate) or it is just your funny style of writing (which is cool).
Fresh deposits as was mentioned. How can the smell of smoke be triggered by a recent fire? Honestly...
This is taken out of context. I mentioned in my first post that I have experience with terracotta stoves, the smell of a smoke is something I am used to when starting a fire and shortly after or even if for some reason the fire is not getting enough air. My complain, the topic starter, was the lingering smell of smoke even after more than 24 hours. This might be normal with a fireplace, it is definitely not normal with a terracotta stove, hence my question.

You can smell the smoke - there, your nose proved it.
The question was about the downwards draft, not smoke. Maybe I wasn't wording it perfectly.

  • The fact that a fire was recently ignited inside the living space.
Again, the question was about lingering smoke smell, 24+ hours after the fire.

I found your explanation about tiny movements interesting, some other topic on this site also mentioned the effect of a forced air heating system. I cannot prove or disprove it, what I can tell is that I used the incense stick both with the furnace running and stopped. In both cases, the movement of the incense smoke moved clearly in the upward direction. I played around the door and the vents of the door, every little crevice around the door effectively sucked in the incense smoke albeit very slowly. In other words: no matter what I did, even with the damper closed, I could still see a minor upwards draft with the incense stick smoke. Of course, this does not mean I covered everything you mentioned, but I still find it representative, the furnace blower is definitely something I expect to have a major effect on the overall pressure in different rooms, as there is no such thing as perfectly balanced feed and return.

I understand the smoke condensing on cold surfaces, I am still reluctant to believe that smell can come back to an extent it gets noticeable. My two reasons: the fire box did not have a noticeable smoke smell, when I stuck my head in briefly; during cleaning I found a bird nest (even egg shells and bird poop) but we never had any kind of smell in the house.

Long story short, I will watch out for outside conditions, what wood am I burning and how long am I burning it. I will probably start a couple more fires to figure it out.

P.S: the bird infestation was because the previous owners neglected the house. We had to rebuild the chimney (the top 10 rows) and that's when the chimney cap was also installed which only happened this year. This means that it was raining in the chimney for at least 3 years since we got the house and there was never any smell coming from the fireplace.


 

stoveliker

Minister of Fire
Nov 17, 2019
4,353
Long Island NY
Extrapolating your incense/candle data while noting that the temps are similar neglects the fact that wind is not constant. Turbulence near.the chimney cap can momentarily push gases in your home, especially when the temps.are such that only a minor draft exists in "constant wind" conditions.

A shirt burst of creosote-contaminated air can create a long lingering smell.

Also,.not smelling anything for years when it was not in use doesn't say much; new deposits will generate new smells.

I'm not saying this is the answer, but if you don't smell anything in the firebox, it has to come down from the chimney, regardless of what your measurement (taken at some point in time, under certain conditions) say.
 
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zsoltc

New Member
Dec 5, 2021
13
SE Michigan
Extrapolating your incense/candle data while noting that the temps are similar neglects the fact that wind is not constant. Turbulence near.the chimney cap can momentarily push gases in your home, especially when the temps.are such that only a minor draft exists in "constant wind" conditions.
This is a fair point, my 5 minutes don't say much, I can't exclude momentary movements. Ultimately my goal of finding out the source is to eliminate or reduce it significantly. If we accept the idea of the smell being caused by contaminated air down the chimney (no matter the mechanism), what is the solution?
Somebody mentioned the inserts because they were unable to cope with the smell. Is this really the only way to eliminate it? I like the idea of a fireplace but I am not sure I would want to spend 2k+$ on an insert.
Stuffing old blankets up the damper would become quite messy after the first use and only closing the damper is obviously not enough.

Let me put this question differently: you guys are obviously using /have used a fireplace, do you also notice a lingering smell of smoke in the first one two days after the fire?
 

Rickb

Minister of Fire
Oct 24, 2012
1,197
St.Louis
Even with my stove I have had a stale smoke smell a few times days after I used the stove do to a draft reversal. Normally it happens when there are large swings in temp during the spring, but it does happen with a cold stove.
 
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NorMi

Member
Nov 18, 2021
110
Northern LP, MI
If you'd like to do some more tests after the house clears of the current smell, there's a few other possibilities to improve your process that might help. The first thing I noticed is you had a smoke smell right at the beginning of the fire, this is common and perhaps the main issue is it simply permeated into your furnishings enough to make most or all of the lingering smell in the house, so try to minimize that.
Open your damper and glass doors at least 30 minutes to an hour before you establish a fire - this will let the stack effect start to create a natural draft and begin to put at least some heat into the chimney. Make sure you have a window cracked so there is always enough makeup air available to keep the draft CFM up, fireplaces take a lot of draft.
Start the fire with a small amount of very dry wood kindling, one or two small splits and a few crumpled newspapers - this should start a hot fire in less than a minute or two, minimizing both the smoking time and smoke volume on startup. Resist using any unsplit kindling, branch cuttings, or unsplit limbs - these often dry slowly and are too wet internally to get a fast, hot start. Make sure you are using a cradle to keep the wood up off the floor of the fireplace. You should not smell smoke in the room when you are starting the fire if the chimney is drafting well enough to handle all the exhaust that is being created.
Make sure your wood is split down small enough, and verify the moisture with a cheap digital moisture meter on a fresh split. Burn stuff that is only under ~20%. Keep your splits under 6" diameter or so. If you hear or see sizzling at the end grain, it's a good sign the wood is far too wet.
Burn at least 80-100 lbs. of wood per session and keep the fire going raging hot at all times. To heat 2-4 tons of brick mass to a good temperature takes a bare minimum of ~200-300k BTU/hr of energy to actually transfer into the brick, which is a slow heat transfer interface at the margin. Getting and keeping the chimney system as hot as possible will minimize the wet creosote formation.
*Don't close the draft down or the doors right away, and clean the fireplace out before you close it down. Use a ash vacuum or a sealed ash bucket to get it all out of the house cleanly.
 
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zsoltc

New Member
Dec 5, 2021
13
SE Michigan
If you'd like to do some more tests after the house clears of the current smell, there's a few other possibilities to improve your process that might help. The first thing I noticed is you had a smoke smell right at the beginning of the fire, this is common and perhaps the main issue is it simply permeated into your furnishings enough to make most or all of the lingering smell in the house, so try to minimize that.
Open your damper and glass doors at least 30 minutes to an hour before you establish a fire - this will let the stack effect start to create a natural draft and begin to put at least some heat into the chimney. Make sure you have a window cracked so there is always enough makeup air available to keep the draft CFM up, fireplaces take a lot of draft.
Start the fire with a small amount of very dry wood kindling, one or two small splits and a few crumpled newspapers - this should start a hot fire in less than a minute or two, minimizing both the smoking time and smoke volume on startup. Resist using any unsplit kindling, branch cuttings, or unsplit limbs - these often dry slowly and are too wet internally to get a fast, hot start. Make sure you are using a cradle to keep the wood up off the floor of the fireplace. You should not smell smoke in the room when you are starting the fire if the chimney is drafting well enough to handle all the exhaust that is being created.
Make sure your wood is split down small enough, and verify the moisture with a cheap digital moisture meter on a fresh split. Burn stuff that is only under ~20%. Keep your splits under 6" diameter or so. If you hear or see sizzling at the end grain, it's a good sign the wood is far too wet.
Burn at least 80-100 lbs. of wood per session and keep the fire going raging hot at all times. To heat 2-4 tons of brick mass to a good temperature takes a bare minimum of ~200-300k BTU/hr of energy to actually transfer into the brick, which is a slow heat transfer interface at the margin. Getting and keeping the chimney system as hot as possible will minimize the wet creosote formation.
*Don't close the draft down or the doors right away, and clean the fireplace out before you close it down. Use a ash vacuum or a sealed ash bucket to get it all out of the house cleanly.
Thanks for the tips, based on all the answers I tend to believe, the smell comes from the chimney. After more than 2 days the smell is virtually non-existent, this morning I think I still felt it but nothing concerning.

I will pay attention to opening the window, using the right wood and try burning more than just a batch. I do have a cradle, it is brand new, I did not even mention it, I didn't think it can cause any smell...

This weekend I am planning on having another session, I will report back, at least to tell about the experience...
 

Corey

Minister of Fire
Nov 19, 2005
2,680
Midwest
Didn't see anything in my quick scan of the thread, but is this a 'single flue' chimney? ...only this one fireplace and no other flue's? It seems that once every couple years someone mentions burning a fireplace/stove and the smoke leaving that flue gets pulled back into an unused second flue (basement fireplace, gas appliances, etc) in the same chimney. That can often lead to a smoke smell indoors. Might also take a peek if you burn again and make sure the smoke isn't doing something weird like swirling around and getting pulled back in an attic vent or similar.

I also don't know how 'tuned' your nose is, but if you're burning something like oak/ash, etc and smell a pine/fir/other common framing lumber smoke smell, that would be a good time to throw on the brakes!
 
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