Pumice chimney Q's

[zoothorn]

Hi chaps over here,

 

I have an 8kW woodburner ( nestor Martin but a bit ropey) into a 10" pumice lined 7m chimney. I was told a pumice chimney is 'good.. if not one of the best types' by my builder, so being pleased I didn't need liner (& chips etc) extra install cost, went ahead like so. 3ft of enamel 6" diameter links stove to start of the old pumice chimney.

 

What bothers me/ worries me, is whether a 10" pumice lined one is more prone to soot build up, to say a 6" liner affair. Sweeping mine, with a drill-driver & rods spinning etc, I'm never too convinced enough soot is removed. I get about one very big handful of black soot, sweeping twice a winter. I do only use it evenings, & only 4 nights a week too.

 

Are there any soot build-up risks ascociated with pumice ones I wonder? Do 6" metal liner additions mean sweeping procedure is alot better perhaps? I do burn 2/3rds softwood ( extremely dry stuff, never ever fir heavy in sap) & 1/3rd well seasoned ash.

 

Thanks for any advice, zoot

 

 

 

 

Edited October 7, 2022 by zoothorn

[joe90]

If you are getting very little soot then your woodburner is working well, I also have a pumice liner and get very little soot in it.

[zoothorn]

40 minutes ago, joe90 said:

If you are getting very little soot then your woodburner is working well, I also have a pumice liner and get very little soot in it.

Hi J, that's an interesting idea.. tbh the one thing I am sure of, is my woodburner -isn't- working well, but that is, with regard to it having some small structural gaps ( impossible to fix, underneath, & @ back). Different point.

 

It's possible the chimney is actually doing fine as you suggest tho: I do have to have it really full to get it going ( & its got a large box, without firebricks as it's designed), in order to get the thing to produce good heat. So much so some parts of the stove have warped.. I think poor quality spain mfr parts as likely as my using it.

 

Thing is I'm just unsure. I don't like this. Can I trust my builder to have inspected the pummice condition really well as he said he did? How do I tell I'm not caking on thick crusty creosote my brush isn't decent enough to remove?

 

Would you be able to hazzard a guess as to what sort of method this was likely built? As I say, it's 10" diameter, round, pumice. If it for eg was a series of pipe sections bonded together, with some fireproof 'chips' or insulative something around, between it & the old brick outer rectangle.. then I have more peace of mind. If it was formed by something firing pumice spiralling round & round, gradually going up, it would be onto some circular something. 
 

It was used before I moved in, it had an LPG stove here ( red big bottles left outside suggests LPG). I replaced this with my woodburner of a similar size. I'm not sure if that gas stove suggests a particular pumice chimney type.

 

Thanks, zh

[markc]

Soot is a sign of poor combustion, no soot is a good burn. You won’t get stuck on “creosote” unless you are burning rubbish … (even then it won’t be creosote).

Is it difficult to light? Or doesn’t draw well? Gas and oil burners pull in their own air (generally) due to pressurised nozzle effect. A wood burner chimney draw to pull in combustion air. It’s quite possible your chimney is too big or not enough air able to get in through bottom of the burner

[joe90]

Yes mine takes a while to get going, the pumice takes time to heat up and draw well. Stop worrying about what the builder did, there is nothing you can do (apart from take it down to inspect it), hot burns and not ticking over is the best way to reduce soot so your doing it right 👍

[zoothorn]

32 minutes ago, joe90 said:

Yes mine takes a while to get going, the pumice takes time to heat up and draw well. Stop worrying about what the builder did, there is nothing you can do (apart from take it down to inspect it), hot burns and not ticking over is the best way to reduce soot so your doing it right 👍

Hi again J, it's not a thing of me over-worrying. It's this..

 

Like an eejet I got too excited wiv me brush rods, & popped the hat off me cowl. Then faffed about ( the rod end stuck in the hat area) panicking. So I fkd the cowl. Needs a new one. Ok, worse mistakes out there.

 

Now, before I buy a new one (Colt birdbarrier std type) I'm wondering you see is it an opportune time to add a metal liner-? I have a strong incling, that my 10" width chimney, at the moment is pulling up & away alot of the heat. As I'm having to stuff it so full ( & generally run it pretty hot continually, to extract room heat from it.. I struggle even so with my back cold all evening on sofa you see). So could be my theory here right, or, could my struggle be entirely due to my very poor room floor mainly simply remaining perishingly cold my stove can't be expected to change). It's impossible to know. Might be 50/50. If so, & lining my chimney now, has a good chance of me getting warmer.. it's a definite must. But who can tell.

 

Also & this I read as definite, having peace of mind that if my pumice chimney is compromised in spots anywhere, lining it is 'safer'. And I think too perhaps, this just seems reasonable to say, cleaning a liner is much easier than my drill-driver-with-rods method. It just seems more sure-footed having 6" to feel a brush cleaning, than 10" you kinda can't feel the brush is in thouragh contact al the time.

[zoothorn]

1 hour ago, markc said:

Soot is a sign of poor combustion, no soot is a good burn. You won’t get stuck on “creosote” unless you are burning rubbish … (even then it won’t be creosote).

Is it difficult to light? Or doesn’t draw well? Gas and oil burners pull in their own air (generally) due to pressurised nozzle effect. A wood burner chimney draw to pull in combustion air. It’s quite possible your chimney is too big or not enough air able to get in through bottom of the burner

Hi markc, ok this is encouraging, as yes I do run it hot. Forced to to try to keep warm. Bent iron grate parts as a result.

 

No it's the opposite perhaps:  it lights fast, & gets going like a train quickly, with the back of box 'door' open  the flames are pulled up (I often wonder whether too much tbh). So the signs are, I believe, that if anything the draw has always been -too much-. I sit up a bit here, end of a small valley & watch weather go sideways in rain sheets for eg, out my side windows: I get pummelled by weather here: so I'm quite sure the wind "across my chimney top" aspect is above-average. I said all this to my builder, & we put in a flue damper, twist it to close a flap thingy. This slows the burn a bit, not hugely, but no idea if it works tbh ( surely if the chimney remains the same, & gap from stove narrowed... the force of air just increaces past this narrowing, equating to a similarity as if it were open.. that's how my mind considers it, & if so, then it's fairly useless; now if foe eg I had the same damper on the -cowl- a hyperthetical sutuation, then this would be different, & the force of air up would be diminished at the stove).
 

I can't really work things out here you see. My builder is a builder, installed lots, but I wouldn't suggest a flue/ stove expert per se. Maybe a liner diminishing the chimney diameter by 4", would result in more heat from the stove, less being pulled up. But maybe a smaller diameter might even -increace- the up draw. Very confused me.

 

Thanks for reading, zh

 

 

[markc]

Morning squire, right a chimney damper is good for reducing draw.  if your fire is raging and bending bars then your combustion is too hot or fierce. Blocking the chimney won’t do it any good and a damper at the top is really bad .. you can reduce draw in windy area with a chimney that spays out at the top like the exit of a trumpet etc but You need to control air into the fire by restricting airflow - thicker bars to reduce air gaps, leaving ash in the bottom or even control fire temp with some green wood (this takes some practice so restricting combustion airflow is best).

[PeterW]

1 hour ago, zoothorn said:

cleaning a liner is much easier than my drill-driver-with-rods method. It just seems more sure-footed having 6" to feel a brush cleaning,

Leave it alone ..!!!! A pumice liner is the Rolls Royce of liners ..!! Do not do anything to it, especially not a stainless liner ..!!

 

17 minutes ago, markc said:

You need to control air into the fire by restricting airflow - thicker bars to reduce air gaps, leaving ash in the bottom

This is your answer - you have to slow the burn at the bottom not the top. Choking the chimney is dangerous and could lead to more issues. 
 

 

[zoothorn]

2 hours ago, PeterW said:

Leave it alone ..!!!! A pumice liner is the Rolls Royce of liners ..!! Do not do anything to it, especially not a stainless liner ..!!

 

This is your answer - you have to slow the burn at the bottom not the top. Choking the chimney is dangerous and could lead to more issues. 
 

 

Aha ok thanks Peter. That sums things upin a nutshell thanks.

 

I can't do anything about slowing the burn at the stove, unfortunately. My fault for agreeing to buy this lemon, once here & found a leg was damaged I agreed a partial refund/ bought new internal parts clearly heat- warped. Then, later I thought to zoom in on the listing.. & -just- saw the leg damage. Dodgy seller then knew it was dmgd when sold. Clearly been dropped on the leg, causing small mishapen gaps all over the shop ( I only found this out later still).. & almost impossible to determine where. Just known there must be some, as it can never be controlled/ rather runs away. A write off, but can't afford 1k min to replace it.

 

Ok so I'll get another standard birdbarrier cowl, without the narrowed liner section in the middle. And stay with my  pumice chimney, albeit 10" which seems not so easy to clean as a smaller one. I don't like this bigger aspect, but if you say it's ok.. I trust you your judgement.

 

I need to consider how better to clean such a big/ wide diameter then. I think I'm scrimping using these drill-driver rods & nylon spinny orange ends. Although this could posdibly be the best way, & I'm doing ok.. I just don't know.

 

Thanks chaps. Zoot

 

 

 

 

[zoothorn]

5 hours ago, joe90 said:

Yes mine takes a while to get going, the pumice takes time to heat up and draw well. Stop worrying about what the builder did, there is nothing you can do (apart from take it down to inspect it), hot burns and not ticking over is the best way to reduce soot so your doing it right 👍

J can I ask, what diameter is your pumice one, & how do you sweep it?

 

zh

[joe90]

Mine is only 6” diameter (but don’t tell @pocster🤣) and sweep it through the stove after removing the inner baffle.