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Old Mill stove backdrafting

Started by Stinny, February 07, 2013, 01:44:18 PM

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Stinny

I have recently moved to a home with an Old Mill wood stove in the basement on a separate short chimney, next to the oil furnace and it's chimney. With temp gauges on my newly installed 8" smoke pipe reading around 400, I've discovered the stove does not like to have new wood added causing a lot of smoke at first... which always reignites in the pipe and chimney with smoke blown back into the basement and out around every joint in the pipe. The chimney is clean... I've burned for years with a Fisher stove and never had anything like this going on except backdrafting on windy days. It also "takes off" at almost any combination of almost closed draft settings, in the firebox or the ash door, as the load of wood gets fully going... not good. Shutting down the drafts will slow the fire of course but has also caused the smoke to reignite.

Obviously I don't trust this stove at all and have only done long burns when I could watch it constantly. I've thought about making an auto damper much like the Ashley stoves that have a metal cabinet around it. That stove's damper has a coil spring connected to it that closes it down if it gets too hot and opens it when it needs air. Any thoughts on all this? Thanks. Stinny
Suzuki 4x4 on Tatou tracks tugging logs in winter

beenthere

Welcome to the Forestry Forum.
Am trying to picture just what you have, and just how this "re-ignition" might be taking place.

You say "short" chimney.  What is 'short' ?

New wood will cause smoke. When you say it "Takes off", what is that?  The same as re-ignition and burning in the chimney? or ?

When you say you are considering adding a damper like the Ashley, leads me to think you don't have a damper control on this stove.

A pic or two would be great.  :)

You may just need to control it by the amount of wood you put into burn. What wood are you burning?
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Stinny

The chimney is about 18'-19' high with an 8"x8" lined flue. The wood is hardwood... maple, oak, ash. The Old Mill brand stoves have 2 rotary draft adjustments on the firebox door and one on the ash door. The backdraft I describe is more like a loud "whoooof" sound which I believe is hot gases re-igniting in the firebox, pipe and chimney. The first time it did it, I was upstairs. It sounded like something slammed into the house. I went down to check the stove and the basement was full of smoke. I've since been able to duplicate the conditions and standing right beside the stove, it gets your attention for sure. I already had the elbow going into the chimney thimble cabled so it can't get out of the thimble. The force I saw might have been enough to blow the pipe out of the thimble without the cable.

The "condition" that causes the re-ignition is when the stove gets to 375-400 degrees
measured on the pipe right near the stove. If I've then had the fire door open and have loaded wood into the stove, then close the door and dial down (something I've done a thousand times with the Fisher stove) the drafts to where I might leave it for the night... the re-ignition happens. I want to run the stove in that range to avoid creosote so this is a problem.

The "taking off" issue is how I describe the reaction this stove has to heating up fast with plenty of new fuel wood added to a bed of coals. Obviously, when the ash door is open, it's getting a lot of air under the fire bed and it will get hot fast. But, close the ash door and set the ash door draft at just one turn open (about 1/8" of airspace of the 3" diameter dial) and the stove will shut down eventually (not enough air)... open the draft to 2 turns open and the stove "takes off"... the hotter it gets, the more it draws thru the draft and the hotter it gets again. The issue is almost the same with the 2 firebox drafts... get them closed too much and the fire goes out... just a bit more and it will maintain where you want it but you have to keep it below the 400 degree zone. Add any wind outside too and "whoooof", it blows the smoke pipe.

I mentioned the Ashley auto draft idea because it seems if I could control the air intake automatically, this stove might be OK. As I said, I've never seen a stove do this kind of blow back this way. Years ago, my father had a pipe blow out of the thimble in the middle of the night with the Fisher stove and somehow got it back in the thimble before it caused a fire or smoke problems. It was windy and the chimney there had a 6" flue in a 40' chimney.

I'm sure interested in any ideas as to why and what I could try to get control of this stove. I mentioned the size of the chimney as this is the first time I've used a 8" flue chimney and 8" smoke pipe (stove has an 8" smoke pipe outlet). Don't have any pix. Thanks, Stinny.


 
Suzuki 4x4 on Tatou tracks tugging logs in winter

beenthere

I think that it is just a matter of finding that draft adjustment between the one turn and two turns, and the right amount of wood to load. Most stoves have their inherent sweet spot between wood and incoming air. You'll find it.

But the "whoofing" is just a combo of wood, heat, and incoming air. Some, or all three, are too much from my experience.

south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Autocar

Sonnds to me your problem is when you add wood you get heavy smoke then she gets some oxygen and the smoke ignited from the hot coals. Just like coal smoke you never never cover up all your coals because she will ignite and blow your pipes clean off your stove.
Bill

Slab Slicer

I agree with Autocar about the "whooof". I get the same thing when I get a smoldering fire in the woodstove. If I don't open the ash door first to let some extra air in, That whoooof will come out the loading door into my face when I go to load it. I haven't had that issue this year. I think we've found that sweet spot, and usually have a nice fire in no time.
2016 LT35HDG25, Kubota L2501 w/ FEL, Kubota BX1500 w/FEL and custom skidding rig, Stihl MS 500i, Stihl MS362-25", Stihl MS250-20", Stihl MS192-18",  2001 F250 SD 7.3, GMC Sierra Dually 6.0 gasser, Peaqua 16" 10K trailer, Sur-Trac 12' Dump Trailer 10K
Chuck

36 coupe

First off your 8x8 lined flue probably measures 6x6.400 degree pipe temp is too high.All wood stoves will woof once in a while.A dirty chimney will cause it.Wood gas will ignite if a stove is opened quickly.My stove has woofed one time this winter so far.Stoves with a thermostat woof often when a fire smolders and the draft opens a bit.Stoves without a pipe damper will run away when a large load of wood takes fire and more smoke is produced than the chimney can handle.

Al_Smith

Open the air up and let it roar a tad bit before you add the new load of wood .

tyb525

Yes, crack the door and get it going a little bit, gets a draft going eliminating smoke and backdrafts. Our damper is always open unless the wind is very strong, using the damper to control the fire causes too much creosote, the vents should be used instead in normal conditions. And yes I got our stove going again a month or so ago, so far so good!
LT10G10, Stihl 038 Magnum, many woodworking tools. Currently a farm service applicator, trying to find time to saw!

Stinny

I always let the stove get air before I open the firebox door by cracking the ash door. Even that doesn't stop the problem if that temp gets to 400. After the stove is closed up, from a new wood load, it can whoooof back as the temp comes down.

Thanks to all for the input. Good to know it's happened to others and that the "sweet spot" issue is common. I guess I've just got to get to know the stove better. Thanks again... great forum!

Stinny 
Suzuki 4x4 on Tatou tracks tugging logs in winter

Al_Smith

Quote from: tyb525 on February 07, 2013, 10:23:56 PM
Our damper is always open unless the wind is very strong, using the damper to control the fire causes too much creosote, the vents should be used instead in normal conditions.
Hmm ,well I'm 65 years old ,been around wood stoves all my life and every one of them had a flue damper  .If they aren't supposed to be used why did they install them?

WH_Conley

I don't think I have ever seen over half dozen stoves installed without a damper. Some stoves have a damper system built in. The reason you are getting creosote is the damper is doing an efficient job of cutting down the draft. Use the damper and open everything up a couple of times a day to clean the flue, you will see more heat for the amount of wood you burn.
Bill

beenthere

I gather tyb was talking a stack damper, vs the vent(s) monitoring air coming into the stove (also referred to as a damper).

For what I can see, the older stoves that were not airtight commonly had a stack damper, as well as adjustable vents.
The airtight stoves seem to skip the stack dampers and rely on adjusting incoming air, some mechanically with a bimetal strip to close when heat was at the upper limit, or electronically sensing the temperature and making air adjustments.

For me, it is mostly a matter of putting the right amount of dry wood in for the heat needed over a given period of time. That takes a fair amount of stove attention, so putting in extra wood and relying on the stove to shut down, will bring on smouldering and creosote possibilities. Not many good shortcuts when burning solid wood.
And a controlled burnout once in awhile is what I do to keep the chimney clean, along with brushing it down a couple times a year.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Al_Smith

No seriously I'm not talking about a 1940's Round Oak or Warm Morning stove here . I have a plate steel  air tight insert made in 1982 and it has a slide damper built into it .My deceased father has a cast iron air tight insert bought around 1987 and it too has a built in slide damper .

Now maybe those "high tech " numbers don't have a damper but if they have electronic control which I've never seen but  just how good is that if you loose electrical power ?

The only stove I've ever seen that did not have a stack damper was a free standing fire place that looked like an inverted funnel or a dunce cap .You can't really choke one of them down else the whole house would smell like a smoked ham,not good .

If you don't have a stack damper all the heat is going up the flue .What good does that do? Warm the hoot owls maybe .

WH_Conley

I have an Ashley Wood & Coal, an airtight. It has the stack damper. My daughter just bought a house about 3 weeks ago that has exactly the same stove that came with the house. It does not have a damper. My SIL remarked a few days ago about my stove seemed to put out more heat than theirs does.

Get a fire going and then turn the stack damper off, not to the point of smoking and stand there a minute, you can feel the extra heat coming off the stove.
Bill

Stinny

As far as the re-ignition or puffing of this stove goes... I have thought that maybe there is too much opportunity for the air/hot gases to form in the hot 8" pipe... I may try reducing at the stove to 6" pipe and then plug into the 8" thimble with another 6" to 8" adapter. Can't help but think it could help as the pipe is what gets to the 400 degrees... maybe the less volume would mean less air in that hot area making it impossible to re-ignite. I know the only way to really know is to try it.

What do you guys think? Waste of time and money? 
Suzuki 4x4 on Tatou tracks tugging logs in winter

36 coupe

Ill try again.400 degrees is close to chimney fire time.You have flames in the stove pipe at that temperature.Ive spent 74 years with wood heat and have never used a wood stove with out a stack damper.My cook stove damper runs about 1/2 way closed, my Mid Moe runs with the damper about 80% closed.When a chimney fire happens the stack damper has to be closed to shut down the air supply.Ive spent 35 years on the fire department so Ive seen all the dumb things people do to burn down their houses.I did fire reports for the dept for many years.On fellow lost 2 houses to a stove that woofed and blew the stove pipe of the stove.He didnt think he needed a damper.Ive used a Riteway 37 stove in my shop since 1968.This stove has a thermostat on the air intake and it will run away if the stack damper is left open.You can fool with pipe sizes but you will have woofing problems until you put in a stack damper and stop filling the stove with wood.Most people who ask for advice have already made up their mind to do the wrong thing.

Al_Smith

After rereading this thing a couple times and debating weather or not a stack damper is need I hit on something .

If you are choking down the fire with the intake air what you are doing is shutting off a source of oxegon to the fire .As it smoulders away it's gassing the products of combustion but due to lowered internal temps plus a lack of combustion air the conditions are not such to ignite the gasses .You open the door and it back fires and singes the hair off your arm .

Now it only makes sense that if you more completley burned off the gasses that one you'd get more heat where you need it ,in the stove not going up the stack .Two and also important the more gas you burn off the less rises in the flue and therefore less creosoting when the gasses condense on the sides of the flue .

With a stack damper you can still regulate the temps to keep the flue upwards of 300 degrees which seems to be the magic temp to nullify creosote accumulation .

Take a look at the ashes .They should be nothing but powder if it's set up right .Not lumpy unburned charcoal .

Al_Smith

More .You have basically three stages of wood burning  ,the flamed log ,the gas produced by same and charcoal .

To build and maintain a good fire you really need to have the fuel in all three stages .The charcoal holds the most heat and is the least in producing the gasses that produce the creosote formation .

For example to bank a fire at night you need to first have a good bed of coals ,then the second layer logs in the burning stage and thirdly the last you put on over that .If you do it right it will hold all night and you haven't a thing to worry about .

You can't let it burn down to just a teeny bit of live coals then toss in a half a wheel barrow full of wood .Close down the intake and sure as God made little green apples it will gas on you .

Corley5

You've got 40' of chimney but is it taller than the highest part of your roof?
Burnt Gunpowder is the Smell Of Freedom

Stinny

Lots of good advice here for sure. Don't know why I didn't mention it in the first post (36 coupe) but the 8" stove pipe has a damper in it... and, it seems the consensus is that I'm choking the fire using the intake drafts only and also letting the temps get hotter than I need to prevent creosote build up. I'll try opening the 2 intake draft dials to give the fire plenty of air to burn and use the stack damper to get the stove to settle around 300 degrees. How's that sound? 
Suzuki 4x4 on Tatou tracks tugging logs in winter

Al_Smith

Sounds a lot better than cooking it off at 400 plus . ;)

No seriously I just think you just have to figure out how to fire the stove .40 foot is a lot of stack but if it worked on another stove there seems to be no reason it won't on this one .

Corley5

Maybe, but it sounds to me like there isn't adequate draught  :)
Burnt Gunpowder is the Smell Of Freedom

Al_Smith

If you have 40 foot of 8" stack it should be I'd think .40 feet of round because of the way the smoke escapes would equal about 10-11 inchs of square .That thing should have plenty of draw unless the birds made a nest in the flue and you've gassed them .

Anything can happen you might have the creosoted body of a stupid raccoon that got stuck going after a bird .I don't think a cat would shinny up that high but cats being cats are not always the sharpest tool in the shed .

If a cat can be dumb enough to climb a tree and not be able to get back down who's to say what they are incapable of .

Corley5

That leads to the question- Is the chimney clean?
Burnt Gunpowder is the Smell Of Freedom

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