Unburned wood in a fireplace

[bo_knows]

I have a fireplace (not stove) with a fairly tight glass door. I've posted a few times here about odor issues, and this may be a totally stupid question, but I can't seem to find an answer after searching.

Is it typical, or OK, to have a couple of charred logs left in the fireplace after a fire? If not, what do you do when you're left with big charred pieces of wood?

Secondly, would said logs contribute greatly to an odor problem in the surrounding area of the fireplace (when the damper is closed)?

 

[jb6l6gc]

In burnt pieces are most likely due to your wood not being dry enough in the center. How long has your wood been seasoned. Also most likely would cause odour as it charred unburnt wood

 

[bo_knows]

In burnt pieces are most likely due to your wood not being dry enough in the center. How long has your wood been seasoned. Also most likely would cause odour as it charred unburnt wood

We're talking some grocery store bought wood (I know). I was simply testing the fireplace out for the first time.

So, if it's causing bad odor... what do I do to dispose of it?

 

[jb6l6gc]

If it is kiln dried at the right moisture level which I still doubt maybe your are going to big to fast on your logs. You do want a decent coal bed when adding larger splits. As far as disposing them. Put them in outside firepit or chimnea if u have one, throw in woods again if available, compost bin, have another fire, many things u can do with it. If nothing else bag and throw out

 

[coaly]

Are the sides angled and are you burning towards the rear wall of it?
Does the glass door have air intake screen or adjustable slots to control air at bottom or sides?
Is this unburned charred wood or all charcoal? (it's fine to use for the next fire and will ignite easier than firewood. Put it in a metal can like you would ashes and store outside until you're ready to use it)
Are you burning with wood raised on a grate so it gets air?
Ash piled up to bottom of grate will slow air to logs as well.

If you clean fireplace are you still getting a smell from chimney? Do you get a whiff of dirty chimney in the summer when near the fireplace?

 

[Supersurvey]

Could it be a creasote smell?

 

[bo_knows]

Are the sides angled and are you burning towards the rear wall of it?

Negative

Does the glass door have air intake screen or adjustable slots to control air at bottom or sides?

On this particular one, it does not.

Is this unburned charred wood or all charcoal? (it's fine to use for the next fire and will ignite easier than firewood. Put it in a metal can like you would ashes and store outside until you're ready to use it)

Seems like a combo of both.

Are you burning with wood raised on a grate so it gets air?

Indeed I am

Ash piled up to bottom of grate will slow air to logs as well.

Hardly any ash in the fireplace. It was thoroughly cleaned when we moved in, and I only have done 2 small test fires.

If you clean fireplace are you still getting a smell from chimney? Do you get a whiff of dirty chimney in the summer when near the fireplace?

It sort of smells if I stick my head in (would it ever not?). We just got the flue repaired (knocked out flue tiles, and put in stainless steel liner), so it really shouldn't have a lot of buildup.

Could it be a creasote smell?

See above answer.

 

[coaly]

Sounds like it needs some sort of air intake. Most doors have an intake built in, maybe they are made for a fireplace with outside air intake? If you have a screen, open doors slightly so it gets plenty of air to see if it burns down readily to ash. If so, an exterior intake with screen with your tight fitting glass doors may be needed.

If it has a smoke shelf, that is an angled back wall that tilts forward with a shelf at the top near damper, it is designed to burn against the back wall. The angled back wall deflects radiation into room and the opening into flue isn't directly over fire. That is how it should be designed.
It should also have angled walls to reflect heat into room. The angled walls at the back are closer to the fire and reflect more radiation outward instead of bouncing back and forth within the hearth. So that is what determines where the fire is placed. Normally it should be against the back wall.
Notice if a fire is built towards the front, it has much more heat loss straight up. A fire against the back wall tends to bounce radiation out into the room. Direct radiation is where most of the heat comes from and glass doors absorb most of this radiation. They do raise temp inside fireplace adding to heat absorbed by mass and prevent excessive indoor air loss up flue. So there is a net gain using them. You can see at times with damper set correctly a screen in place allows the lost radiation into the room, but glass should be closed at night to avoid the huge loss as fire dies. This is how a fireplace should be designed.

The reason I asked about a smell any other times or during summer is if there are mechanical fans or the floor plan is such that there is a large area like second story loft or stairs going up to a second floor that rising heat moves away from fireplace allowing outdoor air to use the chimney as an air intake. If it happens with the fire out, it is slowing the draft which is what is needed to get air into your fireplace opening if the doors are that tight. It's called stack effect and can equalize a chimney or cause it to draft the wrong way.

Did you go with a liner sized for open fireplace or 6 inch for an Insert?

 

[bo_knows]

The reason I asked about a smell any other times or during summer is if there are mechanical fans or the floor plan is such that there is a large area like second story loft or stairs going up to a second floor that rising heat moves away from fireplace allowing outdoor air to use the chimney as an air intake. If it happens with the fire out, it is slowing the draft which is what is needed to get air into your fireplace opening if the doors are that tight. It's called stack effect and can equalize a chimney or cause it to draft the wrong way.

Did you go with a liner sized for open fireplace or 6 inch for an Insert?

Well, this is a 2 story home. Both stories have a fireplace. The fireplace in question is on the 2nd story (the 1st story one has a 6" pipe for a stove that is to be purchased next year, the 2nd story has a 11" fireplace sized flue lined, I believe). The downstairs one always smelled in the summer, and isn't really smelling now in the winter.... now its the upstairs that smells and it didn't in the summer. We've only lived here since May, so I don't have a lot of data points.

You know, I poked my head in with a flashlight, and the fireplace IS shaped like your picture. Whats interesting is the new liner that I paid for this summer doesn't even start until something like 6ft up (somewhere above that little "shelf" of brick). Everything below it is fairly blackened out. If you get a chimney swept, do they do that close to the firebox as well?

We're getting some repairs done to prevent smoke from going up this chimney and right back down the downstairs flue (we're extending the upstairs flue upwards 2-3ft so its not level with the other one). After that happens, I'll try and do a fire that is very far against the back of the fireplace. I'm still pretty worried about the odors though. We'll see if removing that charred log makes a difference.

 

[bo_knows]

Got rid of the unburned wood yesterday and brushed all the ash down the ash dump. Had the flue open, a few candles running inside the fireplace, and the windows open most of the day (it was pretty warm). It smelled fine in the room. Blew the candles out, closed the windows, and closed the flue when we went to bed.... woke up to a stinky room, sadly.

We'll see what the chimney guy says on Tuesday. Sigh. Maybe extending this flue up 2-3 feet will help the updraft (though, does that matter when the damper is closed?)

 

[coaly]

So that chimney is acting as an air supply into the house. Opening a window gives a path of least resistance.
It can be anything from rising warm air in the house, rising through an air leak, or up steps on another floor, or mechanical fan exhausting like a dryer, bath or kitchen fan. Gas appliances like water heater, furnace, either gravity vented up a flue or power vented, they all exhaust indoor air and this chimney is the fresh air source for something. Oil burners use and exhaust indoor air. Radon fans are becoming another factor that depressurize a building. It's all about atmospheric air pressure outside being higher than inside pressure and cooler, heavier night air drops down the chimney helping the already higher outside air pressure to balance inside and out.
When you were smelling it downstairs, that chimney was the fresh air source for something.
Since this can happen when one flue is in use, if flues terminate close to one another smoke can be drawn from one to another, so they should be different heights to prevent cross drafting, but if the likely appliance causing it has it's own air intake, (like fireplace having it's own outside air source) it can be alleviated easier than extending flues.

 

[velvetfoot]

Just as another opinion: Maybe it's coming from the bricks from old deposits. Can air come down around the sides of the chimney liner? Perhaps from the area under the 6' when the liner starts? I bet a nice insert with a blockoff and insert to cap liner wouldn't be smelly, even with some downdraft. I have downdraft that I accept is part of my house at this point, but I never notice any stinky smell in the summer when it is turned off.

Does closing the fireplace damper help? I don't recall you saying you had one.

 

[bo_knows]

Just as another opinion: Maybe it's coming from the bricks from old deposits. Can air come down around the sides of the chimney liner? Perhaps from the area under the 6' when the liner starts? I bet a nice insert with a blockoff and insert to cap liner wouldn't be smelly, even with some downdraft. I have downdraft that I accept is part of my house at this point, but I never notice any stinky smell in the summer when it is turned off.

Does closing the fireplace damper help? I don't recall you saying you had one.

Closing the damper makes it worse. If I wasn't losing heat out the chimney, I could leave it open 100% of the time and not have much of an issue.

I don't think there is room between the liner. They knocked out all the old flue tiles, and put the liner in with some sort of refactory cement.

I know that an insert would solve this problem... but I'm putting an insert in the basement (plus, I just put the chimney liner in... dont want to immediately replace with a 6" stove liner). I didn't want to double my costs here.... which leads me to the rest of your post. Everything I read about says its a pressure problem. We put a radon fan in in the summer. Maybe that changed things? I hear HRV's are stupid expensive too.

 

[bo_knows]

So that chimney is acting as an air supply into the house.

When you were smelling it downstairs, that chimney was the fresh air source for something.

So, whats the course of action here? I do have a lot of exhausting appliances. Gas furnace, 2 bathroom fans, microwave vent, and a new radon fan (as of the summer). Do I need to find specifically which appliance is pulling the most? Can I just put replacement air anywhere? Most importantly, what are the options for replacement air in general? Seems like HRV systems are mentioned on here a lot, but they are pretty expensive.

I saw something like this mentioned in a thread here: (broken link removed to http://www.condar.com/asv.html)

If I have 2 fireplaces (1 upstairs and 1 downstairs) do I put it in the room with the smell problem, which likely has the pressure issue? Or do I put it in the room where I am going to eventually put a stove (different from where the smell is)? Or doesn't it matter?

 

[coaly]

It doesn't have to be difficult or expensive. 3" PVC pipe through basement wall with elbow pointing downward outside with insect screen. Elbow inside pointing upward. I'm retired from my own Propane co. and installed many where gas appliances required fresh air. It was called an "elephant trunk" and the warmer air inside won't drop down the pipe. It will only move into the house when higher pressure outside pushes it in. Some customers didn't like the feel of cold air coming in when a main burner was on, So I explained to them that the burner and diverter hood draw is going to allow any openings or cracks to the outside to leak outside air in. after explaining it was better to have a cold air intake closer to the appliance than migrating cold air through the house towards the appliance, they left it alone. The replacement air is going to leak in causing drafts through the house anyway! That's why I suggested a fresh air intake in the fireplace so when in operation it doesn't starve for air behind sealed doors. It can't compete with a radon blower and gas furnace exhausting indoor air to the outside. It only has the natural chimney draft to cause the low pressure area behind glass and needs higher pressure indoors to push the combustion air through.
If you have a basement window that the furnace and blower can get it's fresh air from, open it and see if it stops the smell from coming down the chimney overnight. You'll probably find no smelly room in the morning.
Does the radon fan run constantly?

 

[bo_knows]

It doesn't have to be difficult or expensive. 3" PVC pipe through basement wall with elbow pointing downward outside with insect screen. Elbow inside pointing upward. I'm retired from my own Propane co. and installed many where gas appliances required fresh air. It was called an "elephant trunk" and the warmer air inside won't drop down the pipe. It will only move into the house when higher pressure outside pushes it in. Some customers didn't like the feel of cold air coming in when a main burner was on, So I explained to them that the burner and diverter hood draw is going to allow any openings or cracks to the outside to leak outside air in. after explaining it was better to have a cold air intake closer to the appliance than migrating cold air through the house towards the appliance, they left it alone. The replacement air is going to leak in causing drafts through the house anyway! That's why I suggested a fresh air intake in the fireplace so when in operation it doesn't starve for air behind sealed doors. It can't compete with a radon blower and gas furnace exhausting indoor air to the outside. It only has the natural chimney draft to cause the low pressure area behind glass and needs higher pressure indoors to push the combustion air through.
If you have a basement window that the furnace and blower can get it's fresh air from, open it and see if it stops the smell from coming down the chimney overnight. You'll probably find no smelly room in the morning.
Does the radon fan run constantly?

Interesting. I can try the window in the basement trick. (I've left the window upstairs open, near the fireplace in question, and that seems to help. I mean, that seems obvious that the smell would dissipate with fresh air there) The radon fan does run constantly, I believe.

So, seems like if that experiment works, and the open window in the basement (with the upstairs damper shut) results in no smell, that putting some form of replacement air device in the basement would be the best.

Again... I appreciate the discussion. I've been obsessively reading about this trying to figure out a remedy. Nobody wants a stinky house.

 

[coaly]

The smell doesn't dissipate, the flow down chimney stops because the open window is a path of least resistance.
That's why when there is a door on a utility room with fuel burning appliances, the door must be vented (or removed) to allow enough square foot area for combustion air. When you can't provide that, you must add an outside air source. Installers of radon systems and central vacs should consider the air requirements for applainces and the rest of the house. A normally aspperated gas appliance uses the gas coming out of the orifice to push air out of the inside of the burner tube. Between orifice and burner is a mixing chamber or mixing tube. Atmospheric air pressure is pushed into the mixing tube to mix with the fuel. Reducing the available air pressure reduces the oxygen entering burner, but the gas pressure stays the same causing a richer mixture. So gas appliances benefit from the fresh air intake as well. The combustion chamber in appliances and wood burning devices for mobile homes is required to be in direct contact with the atmosphere since they are normally installed in a smaller space with control over sealing the structure. Approved appliances have a direct connection to the outside to prevent using any indoor air.

When you have appliances on different floors without adjoining doors with vents, I used to make a mixing box with rectangular vent duct material. Mounted to the ceiling, with an opening into the floor above, openings with vent covers on the box, and connected to an outside inlet with screen. So any appliance on any floor had an air supply. In a basement it also mixes cold outdoor air with mediated basement air and upstairs warm air, so the incoming air isn't outdoor temperature. Now there are codes against venting one floor to another without automatic closing fire dampers.

Opening the window will give the appliances including blowers the air required through the path of least resistance.
Then try your fireplace with an air intake into it or doors cracked and don't be surprised if the wood burns completely.
The air it needs through the doors is not only what it needs for combustion. You're trying to achieve complete combustion. There must be a considerable amount of extra air supplied since there is never perfect mixing of air and fuel. It is common to supply 20 to 40% excess air to assure moderately complete combustion. Supplying excess air is no guarantee that combustion will be complete. A candle flame has virtually no limit to it's air supply, yet under some circumstances, it can smoke, indicating unburned carbon particles. The same is true of a smoldering piece of wood in an open fireplace.

 

[bo_knows]

Update: It's been a warm few days here. Windows open, flue open, no smell to contend with. Last night I closed all of the windows, closed the flue, and opened JUST one window in the basement. There was no smell in the morning at all (or now in the afternoon). However, I'm not 100% conveinced, since the furnace isn't actually pulling any air because its so warm. So... I'm not sure what to think yet.

However, when the chimney guy came, I basically told him the whole saga and asked him about the possibility of a pressure issue. He more or less said that he's never heard of such a thing (sigh). He said my fireplace an flue looked clean, and nothing stuck out to him as odd. He said that I shouldn't be smelling the fireplace from 20ft away, but when he was here there was no smell.

I think that I'm somewhat on my own for figuring this out. We'll see what happens when it gets cold again and I'll report back

 

[bholler]

basically told him the whole saga and asked him about the possibility of a pressure issue. He more or less said that he's never heard of such a thing (sigh).

Find a new chimney guy if he hasnt heard of pressure issues

 

[coaly]

Thanks for the update.
As far as your chimney guy, he should certainly know there are more reasons for a chimney than venting smoke to the outside. The second less obvious reason, and the most important, is to create a low pressure area in a stove or fireplace feeding oxygen to the fire. The entire principal is about creating a pressure differential between inside and outside of the flue. The greater the pressure differential, the greater the draft. Lowering the indoor pressure with mechanical fans decreases the differential, or the pressure the air has to push into the stove. (or through your glass doors) When low pressure areas move over, you will notice a difference with less pressure pushing in. This is made up for by increasing the opening size of intake and adjusting damper for a hotter flue producing more draft to make up for less pressure at the intake. If he knows it or not, his job is all about very minute pressure changes inside and out. Wow.

Maybe you weren't aware of the basics, so knowing the principals helps diagnose most problems. There's not too many ways you can have unburned wood other than lack of oxygen or removing heat. No intake vents on doors or in fireplace and a lack of moving air up chimney caused by mechanical fans is the probable cause of smoldering out before burning completely. Giving it air into the fireplace behind doors will only cure the burning problem and give you a draft through the house towards the exhausting blower or appliance. It would prevent the air coming down chimney, but you don't want the cold air draft through the house toward the offending blower either. The intake into basement makes the furnace much happier, plus the radon fan isn't pulling heated air out of the house.

Is there somewhere else the radon blower, gas furnace, clothes dryer, bathroom fan, kitchen range fan, or any other blowers exhausting indoor air out of the building gets air from? Is that chimney the only opening from indoors to out? (most of these exhaust vents have flaps to prevent air leakage in)
Most fireplaces and chimneys didn't compete with all those exhausting appliances when built. Over the years as these new inventions are added on, the leaks and cracks into the building are no longer enough to supply the indoor air requirements. Caulking, vapor barriers and tighter windows and doors all add to the problem. The path of least resistance becomes the chimney.
If you close every window and turn on a few of these blowers and exhaust fans, try an incense stick or shake out a match in the fireplace and see which way the smoke goes. You may smell or feel a draft coming in, supplying the air for the building. You can Duplicate what happens at night by running the furnace, radon fan and any other automatic appliance that exhausts outdoors during the night. That will show just how much air is coming down the chimney with those items on during the smoke test.
Another test should be done at the gas furnace diverter if it is a natural drafting type furnace. (burners ignite heating combustion chamber that exhausts through a box with large opening into chimney to dilute and cool exhaust gasses) With furnace off, shake a match out at diverter intake to see if air flow is up chimney or being pulled back into house. This could be the intake the radon blower is using when furnace is off. When in use, that's two appliances pulling from another source, presumably the chimney.

There are ways to measure differences between indoor and outdoor air pressure. This is the weight of the air in the atmosphere at any given time at your elevation outside, compared to inside, while mechanical blowers exhaust. Similar to blood pressure using inches of mercury in a U shape tube, this measurement is in Pascals. -10 Pascals is enough negative pressure to experience all sorts of issues including fireplace smoke and smells.

 

[velvetfoot]

Closing the damper makes it worse.

Well, I don't understand that.

 

[coaly]

Well, I don't understand that.

Depends on how you're checking it. An open damper allows the very slow drift to drop through and a couple feet away you smell it just as if you're under it. Close the damper and any cracks or irregularities around damper allows the incoming air to rush through where it can faster. The flue area is trying to supply the same amount of air to replace what is being drawn out of the house through a much smaller opening. Put your nose to it, and it smells stronger since it's more concentrated in that one spot. Just a guess, since when you close the damper, you don't expect any smell, so you put your nose closer to it and hit the sweet spot.

 

[velvetfoot]

sweet spot

or, foul spot