Thermal store/Wood Burner Update (are you sitting comfortably? Then I'll begin)

[www.GymRats.uk]

After what seems like the whole year... possibly because I started when the combi. properly died in April; after much head scratching and many challenges, I have sucessfully ignited the wood burner and it now feeds the thermal store downstairs with hot water for DHW and Central heating.

If you remember my flue dilemma, I eventually went "solid" twin-wall from stove top, up 1000mm then 2 x 30 degree bends into the corner to give clearance to ceiling and roof joists/trusses then a further 3000mm through the attic and out to the sky giving 1500mm protruding above the roof. (about 1200mm above the ridge tiles) Even the tile battens aligned almost perfectly only needing a bit of a trim with the jigsaw to get the

50mm flue clearance. Flashing done beautifully and tiles trimmed sweetly around the flashing boot.

But... there's a story of misadventure to be told as all was not as happy as it should have been.

Attempting to light the stove was impossible, there was zero draft and the acrid smoke spewed into the lounge. Shutting the stove door simply extinguished the weak flames. I spent a week trying to work out what was wrong. I dismantled most of the fire to check air ways and all looked good, poked a tape down from the top of the flue and it want down to a measured 4.5m no blockages. Tried to light it a few more times, putting blowtorch up the stove throat to try and start the draw process, all to no avail. Then started looking at flue fans for the top. Finally out of greater curiosity, I dismantled the firebox once again (so much for worrying about taking the blocks out to sweep!), this time taking out the final baffle plate; all looked fine, so I put my hand up inside the now filthy stove spiggot and felt something soft. Grabbed and pulled, and out came the 4" thick foam plug I'd put in to stop the crap (and tools) dropping into the stove when cutting out the ceiling! What a complete knob!

Re-assembled laid up a pile of wood and fired it up. POW, just like the flue chap had promised, it pulled like a train. Oh frabjous day calloo callay. Smoke billowed out the chimney top as the fire raged and burnt off all the shit deposited from the failed lightings. We were in action.

Had to drill a hole half way up the first section of twin-wall flue to make a pocket for the flue 'stat and now when the inner flue wall hit's

50 degrees the circulation pump kicks in and power to the gas boiler is removed until the fire dies down and gas boiler can take over again.

Still yet to use it in anger with the central heating being on properly but so far it's looking good. chances are that the heat from the wood burner in the open plan living areas will mean the UFH won't actually need to come on while the fire's on at least, certainly not in the big rooms. Might add a bit more of a delay to the gas boiler timer in the morning so initial heating pulls the thermal store temp (at the bottom) right down... A bit more fiddling as the colder months arrive.

Cheers - Pete

[John Rumm]

Yup its a mixed emotion moment isn't it... part joy you have finally fixed the problem, part annoyance when you work out the cause of it in the first place. :-)

(I am sure we have all done similar!)

[SH]

After installing wood burner and flue, did you have it checked out by a competent person who then notified building control and got sign off and give you a HETAS cert?

Buildings insurance can decline a fire claim if there is no valid HETAS cert or if its not been signed off by building control.

[SH]

After installing wood burner and flue, did you have it checked out by a competent person who then notified building control and got sign off and give you a HETAS cert?

Buildings insurance can decline a fire claim if there is no valid HETAS cert or if its not been signed off by building control.

The 4 inch foam plug would have definately been picked up as part of teh smoke pellet test.....

[Brian Gaff]

So how long before the smokeless zone police visit you? That is why around here you will seldom see any open fires or woodburners in use these days. Brian

[SH]

After installing wood burner and flue, did you have it checked out by a competent person who then notified building control and got sign off and give you a HETAS cert?

Buildings insurance can decline a fire claim if there is no valid HETAS cert or if its not been signed off by building control.

The 4 inch foam plug would have definately been picked up as part of teh smoke pellet test.....

[Chris George]

[SH]

Its not clear to me where you are based, but for the purposes of this post, I am going to assume England:

The is a map of the smoke control zones:

If you do fall into a smoke control area then teh following rules apply:

The stove MUST be DEFRA approved model, the approvals list is here:

And any coal you burn MUST be SMOKELESS coal, so normal house coal or bituminuous coal is out.

and any wood you burn MUST be fully seasoned with a moisture content below 20% (use a moisture meter) or buy certified wood:

[www.GymRats.uk]

One or more replies must have have been hidden by my filters, but since January 2022 wood burner stoves must meet the "EcoDesign 2022" regulations which ensures stringent emission and smoke levels are met and must have a minimum efficiency. My own stove is rated at 85% efficient.

"Until the 1st January 2022 if you live in a smoke controlled area and want a wood burner or multi fuel stove you MUST have a DEFRA Exempt or DEFRA Approved stove. After that date the stove must be EcoDesign Approved."

I can confirm that after the initial (cold) lighting that produces a bit of fine smoke but after the main logs have caught alight you can't tell by looking at the chimney whether it's burning or not provided you're burning properly seasoned wood with minimum moisture content there is no visibly nor smell-ably detectable smoke.

There are a couple of air holes towards the top of the back of the fire box which introduce combustion air "into the flame" which I believe helps burn off gases and stuff that would otherwise go up the chimney.

I believe the "Smoke Police" work in the same office as the "Part-P police", formerly known to have driven around in "tv detector vans" They'll not be bothering you although, if your flue outlet routinely blows smoke into your neighbours windows when you're burning freshly cut green wood from the garden then I think the neighbours are justified in making a complaint to the council for "investigation" and the garden-bonfire police might pay you a visit.

I did read somewhere the councils were going to try and urge folks to register their wood burners with them. My rule of thumb is don't tell the council anything, nothing at all. The council is a business, a corporate entity like the police, schools, governments, prime ministers ad. infinitum. They thrive on contractual self incrimination, just like the television licence "fines".

Cheers - Pete

[Chris Green]

What on earth does 85% efficient mean for a wood burning stove? It could be all sorts of things:-

Burns 85% of the wood Extracts 85% of the energy from the wood Loses only 15% of the heat up the chimney

I *suspect* it's the last but even then you're left with the problem that it might not burn the wood efficiently even though the heat it

*has* extracted is used efficiently.

[Tim+]

But what does not burning wood efficiently look like? Lots of unburnt fuel at the end? I think in practice all wood burners will reduce wood to non-combustible ashes so they’re pretty much 100% efficient at burning all the fuel. Obviously burning wet fuel is inefficient but anyone with any sense tries hard to avoid that.

Tim

[www.GymRats.uk]

What does ANY "efficiency rating" mean for any fuel burning device with variable output, variable input, and operational parameters?

I would expect it's down to energy extraction from the known "calorific value" of a specific volume of fuel meeting a specific "operational" criteria running at the typical operating temperature and not under nor over fuelled. Nominal output for mine is quoted something along the lines of 1.2kg <20% moisture log added every 45 to 50 minutes.

" The output listed as the nominal heat output is the nominal output as stated by manufacturer. The lab tests confirm that this output is possible and the efficiency at which the stove runs at this output."

Another less commented upon aspect of the "EcoDesign 2022" stoves is that to minimise emissions to comply with legislation it isn't possible for the air supply to be limited to the point that fuel can be left "smouldering" overnight etc. Therefore more energy is extracted from the wood and less unburnt fuel sent up the chimney as soot etc.

[Chris Green]

No, absolutely not. It *could* burn to very little ash but on the other hand it could leave a lot of charcoal which, in itself, is quite a good fuel. You'd need to analyse how much carbon was left to test that out. Our wood burner usually burns everything but there is always *some* carbon left over.

[Andrew]

well after a few lighting attempts that plug might have caught fire and whoosh, away it would go :-)

[www.GymRats.uk]

I was thinking that if I'd installed a flue fan on the top of the stack as a "last resort" measure to the hidden blockage, potentially it /might/ have overcome the resistance to allow the fire and heat to burn long and hot enough to melt the foam and resolve the problem without me being any the wiser but I think that once the foam started to melt, combined with the high density of smoke the blockage would become impermeable.

Still, it all worked out well in the end.

One other thing I didn't mention:

The stove also has an external air supply spiggot which I've plumbed into a sort of internal riser created when we had a wall knocked out that connects directly to the loft (used to bring all network cables etc from atic into the house).

External air supply is to ellimnate internal air/heat consumption/migration, more relevant to a tightly sealed "passiv" house than an extended 70's bunga-house. This too was a great unknown experiment as to whether strong wind would create a negative pressure in the loft and draw backwards against the flue but having had some high wind days with winds blowing from both sides of the house (prevailing South Westerlys and cold Northerlys) no such effect has been observed. It might be that gusts are cancelled out by simultaneous reduction in pressure at the flue top/cowl but there was no change to the flames upon gusting or prolonged high wind so I'm pretty sure I don't need to worry about backdraft and flame reversal.

Even with the flue now pulling like a train and no fire to feed it's appetite no heat from the house is sucked out and no internal draughts are created so the external air supply appears to have been a great addition. Worst case I could add a hit-and-miss vent to the riser to balance internal and external pressures effectively turning the air supply to an internal source.

Is it a bit strange that in times of spiralling gas prices I'm waiting for some really cold weather to hit so the central heating decides to come on in anger. So far even though I have all room 'stats set to 19 degrees the house hasn't yet dropped below 20 in any room so I've still yet to see how effectively the wood burner and thermal store can cope under full demand and whether I'll have to allow the gas boiler to interject if heating demand gets too high...

Cheers - Pete

[Tim Lamb]

Kindly contain your disappointment!

[The Natural Philosopher]

I have a woodturner in the bedroom with a hole punched straight from the fireplace to the loft, coveerd with a grille. No draughts. Stove draws wonderfully

[SH]

A woodturner? Is that a device for turning logs over to ensure they are seaoned evenly allo ver its surface areas?

[Fredxx]

Yes, I did wonder the need to have a hole in a ceiling for a woodturner. I have a hole too for loft access but have a cover that's left in place rather than leaving it open.

My woodturner can't draw. Perhaps NP has a AI model?