Hi. Yet another question about fire going out

[paullyj]

I have an 35 year old osburn of unknown model similar in size to a current osburn 3500 stove

Its in great condition . we are only using regularly last few years after only using it off and on for the previous 30 years

It runs great plenty of heat with excellent draw no smoke out of flue , just perfect

BUT only with door slightly open

Close the door on a raging fire with plenty of coals with air vent fully open
and the fire goes out immediately . Air nent is working properly

flue is clean and wood is dry dry aussie red gum

There is some but not a lot of rust build up on the metal plate

Can rust and ash block hidden air vent tubing

I found one 1/2 inch hole on inside of fire box that exits via an 1/8 inch hole under front door

This must be some sort of air bleed hole but unblocking it was of no consequence to problem

Replacing this unit is $5000 so i would like to fix it

Any clues on my problem

 

[bholler]

I have an 35 year old osburn of unknown model similar in size to a current osburn 3500 stove

Its in great condition . we are only using regularly last few years after only using it off and on for the previous 30 years

It runs great plenty of heat with excellent draw no smoke out of flue , just perfect

BUT only with door slightly open

Close the door on a raging fire with plenty of coals with air vent fully open
and the fire goes out immediately . Air nent is working properly

flue is clean and wood is dry dry aussie red gum

There is some but not a lot of rust build up on the metal plate

Can rust and ash block hidden air vent tubing

I found one 1/2 inch hole on inside of fire box that exits via an 1/8 inch hole under front door

This must be some sort of air bleed hole but unblocking it was of no consequence to problem

Replacing this unit is $5000 so i would like to fix it

Any clues on my problem

What is your chimney type height and size? What are the outside temps? And what is the moisture content of your wood?

 

[paullyj]

hi

6 inch flue (not insulated ) Insert is inside open fireplace and flue is 20 feet high and cleaned also visually sighted inc cap and fully clean

wood is most definately tinder dry been corded for many years Aussie red wood burns super hot

Its south australia so not too cold like Nth America .

I light when outsde temps drop below 10C 50 f inside it would be about 15 C 60 F

The door is open max 1/2 an inch duplicating air flow possible throu underside vent

a large bed of hot coals and burning wood on top

Doesnt a slightly open door prove that everything else is Ok

Regards Paul

 

[bholler]

hi

6 inch flue (not insulated ) Insert is inside open fireplace and flue is 20 feet high and cleaned also visually sighted inc cap and fully clean

wood is most definately tinder dry been corded for many years Aussie red wood burns super hot

Its south australia so not too cold like Nth America .

I light when outsde temps drop below 10C 50 f inside it would be about 15 C 60 F

The door is open max 1/2 an inch duplicating air flow possible throu underside vent

a large bed of hot coals and burning wood on top

Doesnt a slightly open door prove that everything else is Ok

Regards Paul

Not enough temperature differential between inside and out is most likely causing weak draft

 

[gruesome]

Not enough temperature differential between inside and out is most likely causing weak draft

The temperature difference between inside (=stove intake) and outside air would only matter before the stove pipe and chimney pipe are filled with hot gas, no? After that, the density difference between the hot flue gas and the outside air (and the chimney height) should drive the draft pressure. A few degrees difference in inside vs outside should be negligible compared to the hundreds of degrees difference between the flue gas and either of the surrounding air temperatures. The OP says there is already a good fire going, so the average flue gas temperature should already be quite high, unless there is very little flow and/or there are excessive heat losses along the way.

Could it be the stove connection to the chimney insert is very leaky, or maybe even not really connected? That would steal all the draft, wouldn't it, making the effective flue height very short?

If that connection is good, then I'm guessing there either is a restriction in the stove air inlet, which creates an extra pressure drop when the door is closed, or the stove has sufficient air, but produces too little heat, maybe due to wet wood or insufficient wood load, or there is under pressure in the room or building the stove is drawing air from, which also directly subtracts from the draft pressure. The last two possibilities can be tested (as has been suggested many times before in similar threads) by loading the stove with known dry construction lumber, and by opening an outside door or window in the room the stove is in. I don't know how to test the first possibility without taking the stove apart (but maybe somebody else does).

 

[kborndale]

The difference between 20 degrees and 50 degrees outside makes a large difference on your draft in all stages of the fire. It's the room temp of the stove room vs the outside temp that matters. Yes once you have a good hit fire established your draft gets better but is still strongly influenced by the temps in the room vs outside.

 

[BillBurns]

I preheat my flue with a space heater. Works for me.

 

[bigealta]

paul post a couple pics of your stove and the outside of your house showing the chimney.

 

[gruesome]

The difference between 20 degrees and 50 degrees outside makes a large difference on your draft in all stages of the fire. It's the room temp of the stove room vs the outside temp that matters. Yes once you have a good hit fire established your draft gets better but is still strongly influenced by the temps in the room vs outside.

I completely agree that warmer inside air will give you a head start on draft (i.e. there will be draft pressure and thus flow even before the fire gets started); I do not have enough experience to judge whether that is a huge advantage, or whether a stove should work regardless. (That advantage/head start goes away if you have an outside air kit connected, correct?) My (modern, EPA emissions compliant) stove is sitting outside, has a 10' total chimney height, and starts up and drafts just fine. But all that doesn't help the OP ;-)

Can one measure intake restriction by putting a (suction) blower on the stove flue? But that sounds like it would get rather technical real quick.
I agree that pics would help; maybe include one of the stove connection to the chimney.

 

[gruesome]

I preheat my flue with a space heater. Works for me.

But Paullyj has a draft problem even when the flue is already hot, apparently. That's puzzling. And he's certain he's putting super dry wood on the fire.
My favorite guess is still that the stove pipe is not really connected to the chimney liner, but just stuck into the chimney opening. Easy to disprove by looking, and hopefully posting a picture.

 

[stoveliker]

I think I agree with the OP that if the door is a bit open and the fire rages, that there evidently is decent draft. It needs to be enough to overcome the additional impedance of the air inlet orifices when closing the door, but if it was NOT enough draft for that, I would say that some smoke roll-out and a lackluster fire would be the result with the door open.
That does not seem to be the case.
The flue should be tall enough, I think, at 20 ft (straight up, I presume, given the "looked clean" suggesting one can look from one end to the other) even for marginal (warm) weather.

If the wood has been stacked (off the ground?!) for many (3+) years, it should be fine too.

The home is not sucking air out, as otherwise smoke roll out with the door open would be happening.

This all points to an obstruction in the air inlet system I think, as the OP posited.

OP: if you can pull out a surround from around the insert there could be a plate with model info. That might give you a clue to search for a manual that may show where the air system goes, if you can't figure it out by yourself.

 

[paullyj]

But Paullyj has a draft problem even when the flue is already hot, apparently. That's puzzling. And he's certain he's putting super dry wood on the fire.
My favorite guess is still that the stove pipe is not really connected to the chimney liner, but just stuck into the chimney opening. Easy to disprove by looking, and hopefully posting a picture.

very hard to look as insert is a tight fit in an original open fire

the chimney is about 6 x 3 feet and 20 feet tall

flue runs out the centre of the top the fully plastered top of chimney

Flue must be good I think because if i close door there should be smoke leaking from the supposed leaking flue into house

paul post a couple pics of your stove and the outside of your house showing the chimney.

 

[paullyj]

But Paullyj has a draft problem even when the flue is already hot, apparently. That's puzzling. And he's certain he's putting super dry wood on the fire.
My favorite guess is still that the stove pipe is not really connected to the chimney liner, but just stuck into the chimney opening. Easy to disprove by looking, and hopefully posting a picture.

very hard to look as insert is a tight fit in an original open fire

the chimney is about 6 x 3 feet and 20 feet tall

flue runs out the centre of the top the fully plastered top of chimney

Flue must be good I think because if i close door there should be smoke leaking from the supposed leaking flue into house

Not enough temperature differential between inside and out is most likely causing weak draft

thanks for reply.

but it drafts perfectly with the door just open with a raging fire and large bed of coals

 

[paullyj]

But Paullyj has a draft problem even when the flue is already hot, apparently. That's puzzling. And he's certain he's putting super dry wood on the fire.
My favorite guess is still that the stove pipe is not really connected to the chimney liner, but just stuck into the chimney opening. Easy to disprove by looking, and hopefully posting a picture.

flue looks clean but i would not be able to see any cracks that might let air in or out . Its old but would not have been used 100 times

But with the raging fire and then shutting door smoke should exit every available hole and fill inside of house via the chimney cavity.

chimney is air tight and fully plaster capped where flue exits

 

[paullyj]

But Paullyj has a draft problem even when the flue is already hot, apparently. That's puzzling. And he's certain he's putting super dry wood on the fire.
My favorite guess is still that the stove pipe is not really connected to the chimney liner, but just stuck into the chimney opening. Easy to disprove by looking, and hopefully posting a picture.

Its a good connect from heater to top of flue. If i shut the door you would expect a lot of smoke to enter house as chimney is in great condition . its air tight from top to bottom except a little opening around flue into chimney opening

 

[bholler]

very hard to look as insert is a tight fit in an original open fire

the chimney is about 6 x 3 feet and 20 feet tall

flue runs out the centre of the top the fully plastered top of chimney

Flue must be good I think because if i close door there should be smoke leaking from the supposed leaking flue into house

thanks for reply.

but it drafts perfectly with the door just open with a raging fire and large bed of coals

Yes but it doesn't have enough draft to overcome the resistance when the door is closed

 

[stoveliker]

If it's marginal draft it'll get better (resolved) when it gets cold outside.
If the air inlet is obstructed it'll get not nearly as good when it's cold because the additional impedance of thatnis much larger for the additional cold weather draft to overcome.

 

[Prometeo]

it could be a coincidence, in combination with low atmospheric pressure, or are the combustion air ducts of the stove dirty? try opening a window anyway. I assume that the air lever is fully open and not fully closed... Also check above the baffle if everything is clean

 

[bigealta]

I don't know about that chimney cap? Looks restrictive to me?
Post a pic of your stove too, maybe someone can spot something off.