Proper usage of flue damper on Jotul 118

[Dug8498]

Good morning all. Hoping someone can teach me a little bit about proper damper usage with my setup. I’ve attached pictures below of the stove and the setup. Those aren’t cracks in the ceiling FYI, spider webs. Also, that is not a brick chimney it’s just a brick enclosure that surrounds the fireplace. All houses in this neighborhood were built with these; I think the idea is that the stove heats the bricks. I’m surprised at how well this stove heats our house.

Last winter I burned some awfully wet oak so hot temps weren’t an issue. This year my wood is all measuring 17-22% mc on the freshly split face. This is great, except now my fires are getting incredibly hot and I don’t feel like I have a lot of control over them.

I have one magnetic Thermometer about 12 inches above the flue damper and another on the top of the stove (let me know if there is a better place to put these) I’m guessing I have single wall piping where the thermometer as I can measure such high temps with it?

When I make a fire I close the damper down to just barely open right after it really lights (10 min or so) and I close the circular air intake to about 1/4 open and even then I’m getting flue temp readings above the damper of 900+f. It seems the only way I can get that down to a moderate temp range is if the fire has died down a bunch or I close the damper completely. Is this something I can do? Close the damper completely? I am reading conflicting things about this.

Any advice would be greatly appreciated. FYI- the stove pipe goes through the ceiling in that pic and then pops out the middle of our second story roof so there’s quite a bit of length on it.

 

[Dug8498]

I know this isn’t the most interesting topic but any advice/experience would be greatly appreciated so I don’t do damage to my house/stove


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[begreen]

Three 90º in the flue is going to slow down draft a lot. It might not need the draft damper.

You will have to experiment. If draft is excessive and it is hard to control the stove then try closing down the pipe damper half way once a coal bed has been established and the wood is burning strongly. See how that works. You don't want to restrict draft to the point where the flame goes out or the fire is smoldering that would be bad. If on the other hand it makes the stove more responsive to the draft wheel control on the stove door then it could be a good thing. If it makes no change then try closing it further, maybe even all the way. Just make sure that you are not snuffing out the fire. A steady low and slow burn with a stove top in the 500-650F range is what you are trying to achieve.

 

[Dug8498]

Begreen, thank you for your response on this. I agree, all those 90 turns does seem to be quite a bit but I’m pretty certain I need that damper.

I’ve been running the damper just barely open (maybe 5-10% open) and I’m still getting 700 degree flue temps from that thermometer in the pic and very high stove temps too. I’ve been reading as much as I can on here and although 700 f falls within high end of acceptable range on my thermometer it seems like that’s too high based on what most people here say is ideal and I’m guessing I’m losing a lot of heat up the chimney if that’s the case.

So you’re saying that I theoretically can close the damper all the way. I don’t know a whole lot about the mechanics of wood stoves so I didn’t know if that was a bad idea. My parents have an open fireplace and I know if I closed the damper the whole house would immediately fill with smoke. I will try that out next time after the fire gets going and see if it snuffs the fire out or maybe makes it a bit more manageable.


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[begreen]

Every install is different. You are the best observer of what works well. 700F on a surface flue thermometer is too high. (It looks much lower than 700 in the picture) 700º is ok on the stove top, but that temp is at the high end. Try closing down the flue damper and the air control sooner and burning thicker splits. Yes, it's ok to close the flue damper all the way. It will still pass a portion of the flue gases. It's not the same as a fireplace damper.

 

[Dug8498]

Understood, that’s good to know about the damper. That picture was taken in the morning when the fire was pretty much out which is why it’s reading lower.

All of my larger / heavier splits are oak and hickory which are around 25% mc so I was going to try to use those either next year or the year after. I’m burning the wood I could get dry enough in one summer; not sure all the types but there’s a bunch of birch, maple, and some beech I think; it’s all a lot lighter feeling than the oak/ hickory. May be part of the reason the fires are taking off like they are. I’ll try closing down the air even quicker than I normally do and will try shutting the damper completely if the flue temps are continuing to read that high.


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[Bearle]

Are the door gaskets in good shape? If they aren't they will allow too much air into the stove and make it burn hot. Also i would leave the pipe damper open as they are designed to help retain the heat when closed. Think about it, your essentially blocking off half the pipe when the flue damper is closed and keeping all that heat trapped. Also all the 90 degree bends slows everything down already. Make sure your gaskets are in good shape and you should be able to control it with the air control on the stove. a lot of the time they only need to be open a 1/16 of an inch


Run a lighter around the door while its burning and see if it sucks the flame in anywhere, if it does then you have a leaky gasket. Also not sure how old that is but the top half of the stove is bolted on and sealed with furnace cement. After a long time the furnace cement can actually go bad. I had one customer that we actually had to remove the top half and re apply furnace cement and gaskets and it solved the issue. I didnt even think of that possibility until i talked to Jotul tech about the issues and they mentioned it.

 

[Dug8498]

Are the door gaskets in good shape? If they aren't they will allow too much air into the stove and make it burn hot. Also i would leave the pipe damper open as they are designed to help retain the heat when closed. Think about it, your essentially blocking off half the pipe when the flue damper is closed and keeping all that heat trapped. Also all the 90 degree bends slows everything down already. Make sure your gaskets are in good shape and you should be able to control it with the air control on the stove. a lot of the time they only need to be open a 1/16 of an inch


Run a lighter around the door while its burning and see if it sucks the flame in anywhere, if it does then you have a leaky gasket. Also not sure how old that is but the top half of the stove is bolted on and sealed with furnace cement. After a long time the furnace cement can actually go bad. I had one customer that we actually had to remove the top half and re apply furnace cement and gaskets and it solved the issue. I didnt even think of that possibility until i talked to Jotul tech about the issues and they mentioned it.

No idea if the gaskets are in good shape or not. Great idea, I will definitely check that out. The stove was put in when the house was built, so 1984, 34 years old or so. That’s a great idea and I will try the test with the lighter when I make my next fire. I think I’ve seen other members mention testing by closing a dollar bill in the door and pulling it out.

Should I also test around the top with a lighter as well? I’m not home right now so I can check but I know the very top plate is not meant to be glued on. Begreen told me a few weeks ago that it just lifts off for cleaning and that is correct. I’m guessing that you’re talking about the secondary top box being glued to the main firebox?

Also, wouldn’t it be a good thing to keep the heat trapped closer to the stove assuming the fire was still burning well as it would keep more heat in the stove/ house and allow less to go up and out of the stove pipe? Or is this not how it works?

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[begreen]

Are the door gaskets in good shape? If they aren't they will allow too much air into the stove and make it burn hot. Also i would leave the pipe damper open as they are designed to help retain the heat when closed. Think about it, your essentially blocking off half the pipe when the flue damper is closed and keeping all that heat trapped. Also all the 90 degree bends slows everything down already. Make sure your gaskets are in good shape and you should be able to control it with the air control on the stove. a lot of the time they only need to be open a 1/16 of an inch

Good tip. I was thinking about the door gasket over dinner. If it has never been changed it is definitely overdue. Our F602 however, benefits from closing the pipe damper once the stove was burning strongly. These stoves don't need a lot of draft to perform well. Closing the pipe damper improves control and gives a longer burn. FWIW, our stove has a relatively short flue on it.

 

[Dug8498]

Good tip. I was thinking about the door gasket over dinner. If it has never been changed it is definitely overdue. Our F602 however, benefits from closing the pipe damper once the stove was burning strongly. These stoves don't need a lot of draft to perform well. Closing the pipe damper improves control and gives a longer burn. FWIW, our stove has a relatively short flue on it.

I’d ask the previous owner but he’s not someone we want to keep in touch with so I’ll test it out next fire or maybe just replace it


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[Dug8498]

Figured I would post a resolution to this in case anybody has a similar setup/ question. I moved the flue thermometer up past the 2nd 90 bend and found it was reading lower than where I had it before (pic attached).

I did try running the stove with the damper fully closed, it burned, no smoke came into the house, but it was not burning very well. Stove seems to burn really well with the damper about 75- 90% closed though.

Gasket looked fine and I ran a lighter around the door with a roaring fire and the flame was not sucked in anywhere.

Thanks for the help

 

[bholler]

Figured I would post a resolution to this in case anybody has a similar setup/ question. I moved the flue thermometer up past the 2nd 90 bend and found it was reading lower than where I had it before (pic attached).

I did try running the stove with the damper fully closed, it burned, no smoke came into the house, but it was not burning very well. Stove seems to burn really well with the damper about 75- 90% closed though.

Gasket looked fine and I ran a lighter around the door with a roaring fire and the flame was not sucked in anywhere.

Thanks for the help

View attachment 231518

Is there a stainless liner run inside that old class a chimney?

 

[begreen]

That sounds about right, the 3 turns are slowing down draft already. Draft will get stronger when it's colder outside.

Flue temp will read high as the flue gases slow down. Try putting the thermometer about 6" above the flue damper and see what it reads there.

 

[Dug8498]

That sounds about right, the 3 turns are slowing down draft already. Draft will get stronger when it's colder outside.

Flue temp will read high as the flue gases slow down. Try putting the thermometer about 6" above the flue damper and see what it reads there.

That's where I had it originally and I was getting readings of 700-900+ F. Is it not in a good location where I currently have it?

 

[Dug8498]

Is there a stainless liner run inside that old class a chimney?

I'm not sure! We requested that the previous owner have the chimney swept/inspected when we were buying the house. The contractor found a crack in something (the liner I assume) and the previous owner replaced it right before we moved in. I will find the paperwork and let you know what was put in. Why do you ask?

 

[begreen]

That's where I had it originally and I was getting readings of 700-900+ F. Is it not in a good location where I currently have it?

The previous picture showed it on the elbow. I didn't know you had it lower than that. Flue gases are naturally going to cool off as the stove pipe radiates heat. Around eye level is where a surface thermometer is normally placed.

 

[Dug8498]

The previous picture showed it on the elbow.

Yes you are correct! Before I took the original pics a few days ago, I had it a bit lower, about 6-8 inches above the damper, and it was reading very hot even with the damper mostly closed, then I moved it up another 6 inches to the elbow shown in the first pic (still reading very hot). Then I moved it past the elbow (shown in the last pic). where it is currently I am getting somewhat normal readings (300-400).

 

[Dug8498]

The previous picture showed it on the elbow. I didn't know you had it lower than that. Flue gases are naturally going to cool off as the stove pipe radiates heat. Around eye level is where a surface thermometer is normally placed.

That makes sense. So if I'm getting temps that seem pretty high right above the damper, and then temps that are acceptable after the 90 degree bend, can I stop worrying about causing a chimney fire? My wife is newly pregnant so I'm trying to make sure I'm being as safe as possible.

 

[Dug8498]

I'd like to add here that I may also be closing down the air too late; I really don't know what I'm doing yet. I thought I was doing this soon enough but I may need to do it even sooner. I read something interesting posted by Begreen on another thread a few min ago that I think may have answered some of my questions; quoted below from the other thread:

"It takes time for the mass of the stove to heat up, even though the firebox is already up to temperature. Waiting too long to start turning down the air wastes fuel and can cause flue temps that may exceed the pipe rating. It's better going with flue temp than stove top temp. Start turning down the air when the probe flue temp is around 400-500º. (Surface flue thermometer temp around 250ºF)"

 

[Dug8498]

Is there a stainless liner run inside that old class a chimney?

Bholler, to answer your question, we have a 25 foot tall, 6" diameter, stainless steel liner.

 

[bholler]

Bholler, to answer your question, we have a 25 foot tall, 6" diameter, stainless steel liner.

Ok what is the class a pipe about then?

 

[Dug8498]

Ok what is the class a pipe about then?

I’m not sure? Is that the thicker pipe going into the ceiling? I’ve attached the inspection notes as well as the paperwork for the liner installed last November. Looks like it was a good thing that we stipulated a chimney inspection...

 

[begreen]

That makes sense. So if I'm getting temps that seem pretty high right above the damper, and then temps that are acceptable after the 90 degree bend, can I stop worrying about causing a chimney fire? My wife is newly pregnant so I'm trying to make sure I'm being as safe as possible.

Burn dry wood and chimney fires should not be an issue with those temps. Experiment with closing down the air quicker and just keeping it open a hair, like 1/16 to 1/8".

 

[Dug8498]

Ok what is the class a pipe about then?

Burn dry wood and chimney fires should not be an issue with those temps. Experiment with closing down the air quicker and just keeping it open a hair, like 1/16 to 1/8".

Awesome thank you