Stovax Stockton 7 help needed

[Alycidon]

5 hours ago, openspaceman said:

I noticed my Morso had much less draw than the Jotul 602 it replaced and I put it down to the more tortuous path the primary and secondary air take, especially the fact the flow over the glass is a downwash so it is running counter to heat rising and thus doen't really draw well until there is a good hot flow up the chimney.

This is typical of many modern stoves,  air now tends to enter the stove from the base at the rear so that by the time it gets to enter the firebox along the top line of the glass its superheated.

 

The other issue is many stoves are fitted with an upper and lower baffle plate arrangement,  this holds the heat in the stove for longer and helps efficiency but can create issues with draw.    If necessary remove the upper baffle and try the stove without it in place.   I have known a few Morso's have this issue.

 

Modern stoves really need a minimum draw up the flue of 12PA,  a 10 year old design would work perfectly well on 8PA.   Ultra efficient, ultra clean stoves require a better performing flue.   Pull can be boosted either with a wind driven rotary cowl or an electric draft booster cowl.

 

A

[Stubby]

14 hours ago, Alycidon said:

Modern stoves should be airtight,  older ones less so.   It is highly likely the Olymberel which is a budget stove is leaking air into the firebox from all sorts of places hence its free burning. 

 

The Stockton 7 is nominally rated at 7kw,  as such it does legally require an outside air vent being installed unless the installer considers that the  house has adequate natural ventilation.   This would usually be things like gaps under the doors and around the windows,  pretty unlikely I would have said in these days of double glased everything.

 

So air supply could be a problem.

 

How is it installed ?,  ideally it should be on a 150mm diameter flex flue liner.  No liner and your pull can be radically reduced depending on the house chimney diameter.  Think you said the house was old so likely to have a very large chimney and have lime based mortar between the bricks or stone.  This really does need to be lined.  How high is the flue,  the higher the better.

 

Fuel size,   for optimum performance load 2 or 3 logs at a time,  loading one big one and you wont get the turbulence required in the firebox.  I am taking for granted that the fuel is dry,  ie 16% or below.

 

Air controls,  refer to your Stovax user manual,  usually the primary air going in under the fire is for lighting only on wood or for use with solid fuels.

 

Once the stove is going close the bottom ( primary) air supply and manage the fire purely on the secondary air supply coming in above the fire. 

 

Finally are there any trees or buildings taller that the top of your chimney, if so winds could be blowing down onto your roof and flue preventing the smoke getting out and severely reducing pull.

 

A

 

 

Agree with all the above except the 16% moisture or lower bit , but lets not get into all that again ! ?

[Stringman]

21 hours ago, Alycidon said:

Modern stoves should be airtight,  older ones less so.   It is highly likely the Olymberel which is a budget stove is leaking air into the firebox from all sorts of places hence its free burning. 

 

The Stockton 7 is nominally rated at 7kw,  as such it does legally require an outside air vent being installed unless the installer considers that the  house has adequate natural ventilation.   This would usually be things like gaps under the doors and around the windows,  pretty unlikely I would have said in these days of double glased everything.

 

So air supply could be a problem.

 

How is it installed ?,  ideally it should be on a 150mm diameter flex flue liner.  No liner and your pull can be radically reduced depending on the house chimney diameter.  Think you said the house was old so likely to have a very large chimney and have lime based mortar between the bricks or stone.  This really does need to be lined.  How high is the flue,  the higher the better.

 

Fuel size,   for optimum performance load 2 or 3 logs at a time,  loading one big one and you wont get the turbulence required in the firebox.  I am taking for granted that the fuel is dry,  ie 16% or below.

 

Air controls,  refer to your Stovax user manual,  usually the primary air going in under the fire is for lighting only on wood or for use with solid fuels.

 

Once the stove is going close the bottom ( primary) air supply and manage the fire purely on the secondary air supply coming in above the fire. 

 

Finally are there any trees or buildings taller that the top of your chimney, if so winds could be blowing down onto your roof and flue preventing the smoke getting out and severely reducing pull.

 

A

The Stockton is quite a few years old but that is something to consider.

Although we do have inefficient double glazing there are large gaps under the doors, and bare floorboards  so there should be a good draft, But i will certainly try  opening the window to see what effect that has.

 

Its installed on a 150mm liner and i would guess the height is 20ft plus no trees or anything getting in the way

 

"Once the stove is going close the bottom ( primary) air supply and manage the fire purely on the secondary air supply coming in above the fire."

 

Thats the crux of the matter that often we have to have the top full open and then the bottom partially open.

 

Wood is well seasoned chestnut never less than 18% before it goes into the woodshed so probably around 15% by the time it gets burnt.

I will try the wndow option then at the weekend will have a good rummage around the inside.

21 hours ago, Alycidon said:

 

 

 

[Stringman]

A slight update.

I Had a rummage around in the stove, moved the baffle plate up and down a bit and slid it back a bit.

I made sure i used the logs were slightly smaller.

The fire performed much better. I made sure it was really burning well before i shut the lower vent off.

then we could control the fire from just the top vent.

One thing to ask though.

As a rule of thumb when the fire is established i tend to turn down the top vent until I cant really hear any induction roar - more of a chuckle. Does this sound  correct or should it be more of a throaty chuckle or the full on induction roar?

 

Many thanks

[Dan Maynard]

A slight update.
I Had a rummage around in the stove, moved the baffle plate up and down a bit and slid it back a bit.
I made sure i used the logs were slightly smaller.
The fire performed much better. I made sure it was really burning well before i shut the lower vent off.
then we could control the fire from just the top vent.
One thing to ask though.
As a rule of thumb when the fire is established i tend to turn down the top vent until I cant really hear any induction roar - more of a chuckle. Does this sound  correct or should it be more of a throaty chuckle or the full on induction roar?
 
Many thanks

I run mine with a low roar, that keeps the air washing down the glass and also makes sure the burn is nice and hot. Ideally the flames should burn blueish once the initial yellow flare up has gone after a log is added.

If you close it too much then the draft goes and the flames get lazy and yellow, these will be making smoke which you don't want as more likely to deposit soot in the chimney.

[Stringman]

Dan,

many thanks for that. I have just turned it up a bit and can hear the air being sucked in. I have a lovely window of flames but very few blue flames, and only the bottom part ( though the glass needs a good clean) even when fully roaring there is hardly any blue tinge

 

[Stubby]

17 minutes ago, Stringman said:

Dan,

many thanks for that. I have just turned it up a bit and can hear the air being sucked in. I have a lovely window of flames but very few blue flames, and only the bottom part ( though the glass needs a good clean) even when fully roaring there is hardly any blue tinge

 

On my Burley I can shut it down so that the flames are sorta dancing above the logs seemingly not touching them . I think this is burning the gas from the wood .

[Dan Maynard]

Dan,
many thanks for that. I have just turned it up a bit and can hear the air being sucked in. I have a lovely window of flames but very few blue flames, and only the bottom part ( though the glass needs a good clean) even when fully roaring there is hardly any blue tinge
 

Yeah maybe bluish orange is a better description. When the wood first goes on you get a lot of yellow flame and then as this burns off it goes more orange. It also depends on the wood, so the lighter wood eg pine tend to burn more yellow, elm oak will be less.

The main thing is to have the fire burning hot, that helps with complete as possible combustion and keeps flue temp up so that you don't get tars condensing up there. I clean my glass very rarely because the air flow down it keeps it clean.

[neiln]

I think the blue flame is carbon monoxide burning.  Different gases burn with different colours, the cellulose in the wood first oxidises to form CO, and that then burns with the blue flame.  The yellow flames you get from a fresh log are much more the resins/turps burning.

 

For least smoke you want vibrant, dancing flames.  I suspect the Stockton 7 will have an audible roar.  My 5 with smoke control kit is always audible.

 

Playing with mum's Franco belge (that stove is always quiet, vibrant flame or not) I love the 'constant lazy flash over' stubby refers to, the smoke burning several inches above the logs.  I can set it so the flame looks clean and the chimney emissions are too to the eye, but I'm sure with measuring equipment this state is much dirtier.  It does however seem to be more efficient, virtually as hot as with more air, but a couple of logs last twice as long.

 

Anyway, for clean, vibrant, dancing flames.

[openspaceman]

15 hours ago, Dan Maynard said:

Yeah maybe bluish orange is a better description. When the wood first goes on you get a lot of yellow flame and then as this burns off it goes more orange. It also depends on the wood, so the lighter wood eg pine tend to burn more yellow, elm oak will be less.

I think this bluish orange is the area to aim for.

 

As you say if you put a dry bit of softwood on it rapidly evolves offgas ( the results of heating the wood is pyrolysis which means splitting the wood components by heat). This offgas then burns in what is known as a diffuse flame, the oxygen enters the fuel rich gas from the outside, the oxygen then further splits away the hydrogen and burns as a flame but leaves the carbon particles glowing yellow in the flame until enough more oxygen diffuses into the flame and oxidises this carbon. This is where a jet of hot air aids turbulence. If enough oxygen cannot pass into the flame before it cools down (mostly by radiatingto a cool surface) the carbon particles reform to a mixture of sooty particles, some of the carbon atoms reform in the heat to tiny plates of graphene, a single layer of graphite, graphite resists oxidation so once formed these sooty particles tend to carry over into the flue. This is why it is important to keep the combustion chamber hot and with enough residence time for the flame to be able to burn out.

 

 

My take on this by observing the glass window on my little Morso II, is that you really need to see all  the flame within the box to cut soot. Even so I have noticed, as the firebox is small, if I put a dry piece of wood on top of hot coals the sudden evolution of offgas overwhelms the ability of the downwash secondary air and the excess air holes half way up the back of the firebox and I can see sooty smoke. This happens with birch and holly for some reason, of course we know birch has an oily bark but holly? The only way to avoid these yellow flames going up the flue and being quenched is to cut the logs smaller, and not to load above the level of the excess air holes, so less offgas is suddenly evolved and there is adequate air to burn it.. That is a bit of a challenge to me.

15 hours ago, Dan Maynard said:

The main thing is to have the fire burning hot, that helps with complete as possible combustion and keeps flue temp up so that you don't get tars condensing up there. I clean my glass very rarely because the air flow down it keeps it clean.

The main thing is to keep the combustion hot enough with adequate air to burn the tars before they get the chance to enter the flue. Wood moisture is the biggest  culprit for lowering the temperature in a modern insulated firebox.