stove and chimney

[StudWall]

Hello everyone.

I've got an FDC 5kw ti multifuel stove which was fitted in the summer of last year to my existing chimney (apparently liner not required) and have been well and truly chuffed with it so far.

When it was first used it would kick out heat like mad, getting the room so hot I'd have to turn it down through the risk of melting my face off!

In about October / November I had the chimney swept by a pro and he said all was good but I should stop burning house coal in the stove because it produces a lot of soot, although the amount swept was 'reasonable' and apparently 'good quality soot' this advice I have since followed.

Since then I have burned just seasoned wood and some offcuts of timber from work (untreated) all measured to be around 20% or less moisture, except at the weekend when I also use some smokeless coal.

It gets lit most evenings and Saturdays starts earlier

Over the last month the stove seems to be underperforming, getting the room warm, but not scorching (OK it has been a bit chilly recently but after 4 hours of burning the temperature raised by about 5-6c whereas it used to be about 15c hotter than when I started)

Last night I lit it up again and it pretty much wouldn't burn anything, good seasoned hardwood just sat there smouldering and even nice dry offcuts failed to flame more than youd expect from a zippo.

My first thought was air supply, so I opened a window to provide some clean air, this didn't help, I played around with the vents (even though I'm pretty happy with how they usually work) and this didn't do much either, opening the primary air on the bottom gave a bit more flame but nothing substantial, so this evening I decided to give the chimney a sweep and this is what I produced:

View media item 89813
There was some more which I vacuumed up and a little more which ended up in the carpet despite my best efforts (must buy a Vax) is this amount of soot normal???
Its all very fluffy black, almost like talc, but a whole bucket full after a couple of months doesn't seem right to me, of course it could be that my pro sweep a few months ago didn't do a very good job (it only took him about 15 mins which does seem quick, I spent about an hour and a half sweeping all that out)

And could this be the cause of my poor stove performance?

Your thoughts would be much appreciated

 

[Burnerman]

Just a couple points if I may....
Are you removing the baffle from within your stove, or sweeping through an access door
Is there a register plate fitted to seal the flue pipe where it enters the chimney
Can you see the brush actually reach the top of the chimney pot, or is there a cowl up there?
John

 

[StudWall]

I removed the baffle from the top of the stove and used a standard chimney brush on drain rods through this opening.
There isn't a register plate because it sits into the existing Milner chairbrick.

Yes it did definately reach the top, I saw it come out the top of the chimney when I went outside to rescue my cowl which I pushed out

 

[Burnerman]

Ha yes, we've all done that
The scenario that I find with stoves without a liner is that for example, the stove pipe is 5", yet it pokes into a void much larger, say 16" traditionally.
So, my 5" brush sweeps the flue pipe fine, yet just rattles around in the chimney void above - can you see my drift?
Also, the register plate needs to be sealed to avoid air going up the flue but not through the stove....preventing any small soot fall and unnecessary draughts.
Anyway - your chimney must be clear to a large degree ( where did that extra bucketful come from?) so maybe it's the damper inlets are blocked or not opening to the extent they used to.....try vacuuming around them, maybe?
Personally I use ovoids rather than house coal which has a high bitumen content hence more soot, but that's up to you.
I guess you could try a smoke bomb in the stove to see how that draws, and also see the damper function working.
Has the top baffle distorted badly?
As the stove initially performed well, and there's been no interference with surrounding buildings and so on, I fail to see why it can't perform again..... Bit of a mystery!
This stove doesn't draw combustion air from below or from the lower sides, does it?
John

 

[StudWall]

I see your point, mine has a 6" flue spigot which at the moment just goes into the existing cavity, so I can just get my big brush through this hole and sweep as if it were an open fire.

The bucket of soot is what I swept out yesterday, and is what has built up since it was swept by a pro a couple of months ago, since then I've only burned clean dry wood and a bit of smokeless.
I suspected that it seemed a lot for such a short time and burning good wood, especially as I've a bungalow so a short chimney already.

The stove has 3 air vents. First at the bottom of the door which is the primary air, second is at the top of the door which is airwash and a third which is self regulated air intake for the secondary combustion which enters under the door and flows to some vents at the back, all seem clear and I gave it all a damn good vacuum yesterday too.

 

[Burnerman]

Just at risk of stating the bloomin' obvious here, but if air can enter the stove, and there aren't any obstructions within then the fault must lie with the flue.
Presumably there's no difference in combustion with the ash box or main door open?
In situations like this, (no liner ) I do sweep down from the top - single storey of course!
Do you ever get smoke tumbling back down, as in a down draught situation?
John

 

[StudWall]

opening the door did make it burn a bit better, as did opening the primary air vent, but not overly so, never had a downdraft situation, some smoke comes into the room when the door is opened but thats all.

I initially suspected a draw issue after the glass turned black, just from lighting kindling, which I never had before.

I haven't fired it up since I swept it, so will do that tonight and see how it goes.

Is that amount of soot normal for 3 months (ish) use?

 

[Burnerman]

Soot quantity wise, I guess it's impossible to say but now that you know the flue is clean, you can see how much you produce from now on.
I'd say that was a fair bit of soot for a single storey building!
Are you game to sweep from the top? (at least you'll be able to pop the cowl back on ) Hopefully it is a cowl suitable for solid fuel?
John

 

[StudWall]

i could give it a sweep from the top, might as well if i go up there to refit the cowl.

on that note the cowl is one of these

i started the stove this evening, 6 bits of smokeless on the bottom (homefire at the moment, used to use blaze) and plenty of kindling and firelights, got roaring to start with the door open, when all burning well, put a small log on top and left it to catch, when it was burning, closed the door (leaving the vents open) and bam, almost immediately stopped burning and just smouldered and blacked up the glass,

so i can pretty much narrow it down to either:

- wood not seasoned enough (measured around 15-18%)
- airflow problem with door closed
- wood may still be too big with stove still relatively cold and no buildup on the grate yet

this evenings plan is to try some more scrap softwood and also try cutting up a few of my hardwood logs into smaller bits and see if that burns any better

 

[Burnerman]

It's an airflow problem....has to be.
Of course, if smoke can't get out, air won't go in!
My own stoves (Morso Squirrel 5 kW ) are responsive to the air door at the bottom....even if the wood is damp (and yours isn't ) it would at least show some glowing attempts.
I leave the air wash damper fully open always.
The cowl looks ok - mine has a bigger mesh area - but as it's not on now anyway that doesn't matter.
I'd go for damper dismantling, I think.
John

 

[StudWall]

i got a toothbrush around the airwash intake, a little soot swept out but nothing major so i know that is clear, the lower (primary) air i can see is clear.

I tried some softwood offcuts and boom, it roared like it was new, did a couple of those and seems to be working fine.

I also split some of my hardwood into small peices and put some on, instantly i can hear hissing and, what looks like steam, coming off these peices. after a while they caught on nicely and are burning well also.
It seems that although my hardwood measures under 20% it somehow has a lot of moisture

 

[Burnerman]

Maybe your meter isn't all it claims to be....mine is made by Stihl but any cut wood is left for at least a year, and longer if it's hardwood.
Personally I don't think I'd change back from ovoids to coal but that's entirely personal preference.
Keep warm!
John

 

[StudWall]

that is possible, its a brennenstuhl from Amazon, about £15.

thanks for all your advice

 

[geraldthehamster]

What sort of wood are you burning and how long has it been seasoned for?

Cheers
Richard

 

[richardrich79]

Your problem definitely sounds like an air supply problem so checking out the air wash controls should sort it out.
Have you made any changes to either the air supply for example blocking airbricks or fitting double-glazing. We once had a big old monster of a stove that starting behaving in a similar manner to yours after fitting new windows and solved the problem by fitting a new air vent in the floor.
Whilst I would advise avoid burning house coal as in my experience it can burn too hot and distort baffle plates etc, I'd be tempted to try a shovel of coal to see if the stove performs as it did when new.