Wood burners

[SamT]

I was under the impression that the heat in your fire would be pulled up the COLD chimney first before heating up your stove and therefore you're room. Please correct me if I'm wrong but I've had a conversation with a hetas engineer.
And also my chimney is 500 years old and 5 foot x2 which takes a lot of heating if not installed correctly

Not sure what you're getting at.  A cold chimney/flue never draws well, once its warm the hot gases in the flue will all rise, creating a much better draw.  An insulated flue liner heats up quicker, thus produces a good draw quicker.  I remember as a child trying to get fires 'drawing'.  Occasionally ending up with the living room full off smoke from back drafts/down drafts.  Once the chimney is warmed through, no bother. 

To try and visulise it, think if the cold air in your flue as water, and the warm air in the fire box as air bubbles.  Initially, with only a few small bubbles, these will rise up the chimney, fighting against the restriction all the way up, and some of the cold water will sink back down the flue to replace the 'space' the bubble vacated below.  Once up to temp. the whole flue is "all bubble" rising up, with no more water in.

 

[ChrisJC]

And that's where you let yourself down.  That's that attitude that over the decades has gotten us where we are,  the "f*** it" type of attitude that pumps my nads.

Perhaps my point isn't clear. What I am trying to say is that just having a well meaning piece of legislation to 'green' something isn't good enough. It must take a holistic view of what it is trying to achieve. In the case of Drax, the idea of running a power station on biomass is laudable. However, if it comes from green timber chopped down in the US, kiln dried with gas powered kilns, then shipped 3000 miles to the UK on lorries and ships, then burned, perhaps the overall CO2 emissions from the process are actually worse than the coal that it is supposed to replace. So the net effect is worse for the planet, and worse for the coal mining industry.

Sadly we have a habit of making well meaning legislation that fails to look at the big picture, particularly environmental legislation.

Chris.

 

[SamT]

It must take a holistic view of what it is trying to achieve. In the case of Drax, the idea of running a power station on biomass is laudable. However, if it comes from green timber chopped down in the US, kiln dried with gas powered kilns, then shipped 3000 miles to the UK on lorries and ships, then burned, perhaps the overall CO2 emissions from the process are actually worse than the coal that it is supposed to replace. So the net effect is worse for the planet

We can certainly agree on that.  Hence my comment re the Port Talbot plant.  (the stuff burnt at drax was local).  But its still no excuse to be burning coal and whilst you may have some whistful sympathy for the coal miners of the 80s, that industry is (in this country at least), and in my view rightly so, consigned to the history books.  We have the technology, the economic means and just lack the government wherewithal to implement low carbon alternatives.

 

[Fulk]

SamT:

Ideally, you should use a small 4" flue liner (for a small 5 or 8 kW stove) to keep the velocity of the flue gasses higher, ensuring they get up and out the top of your flue before cooling.  However, building regs stupidly says its got to be 6 inches, for some unknown reason.

Well, we have a wood-burning stove rate at a nominal 4 kW; the manual that came with it specified that the flue should be 5 to 6 inches in diameter.

 

[Fulk]

incidentally, ours is an 'inset' stove (not what we really wanted, actually), but it's very efficient at heating our siting room.

 

[SamT]

SamT:

Ideally, you should use a small 4" flue liner (for a small 5 or 8 kW stove) to keep the velocity of the flue gasses higher, ensuring they get up and out the top of your flue before cooling.  However, building regs stupidly says its got to be 6 inches, for some unknown reason.

Well, we have a wood-burning stove rate at a nominal 4 kW; the manual that came with it specified that the flue should be 5 to 6 inches in diameter.

Shrug  -  principal still applies, narrower the flue the greater the velocity of the flue gasses, less the chance of tar a nasties building up.  Obviously it has to be suitably large enough to cope with the volume of gases being produced.

 

[SamT]

Just as an aside - can everyone stop using the word 'efficient'  incorrectly.   

I have to deal with it every day at work and it pisses me off.

Your stove is very 'effective'  or 'good' at heating your room.


To use the word efficient, you always have to be considering two quantities, a ratio, a percentage.  In this case, its raw energy in (logs), heat energy out.  I suspect your log burner is not at all "efficient" as a large proportion of heat energy goes up out the flue, not into the room, especially if its an inset.

But that's not to say it doesn't effectively heat up your room to a nice cosy temperature, since the proportion going into the room is sufficient to heat it.

[/rant]

Also - human thermal comfort is a funny and fickle thing.  We actually feel quite comfortable when presented with 'radiated' heat.  The warm sun on your face, even though your on top of a ski resort at 3000m  in the alps,  stood in front of a bonfire on Nov 11th, even though the air temp all around you is only 3 deg.

Big black iron stoves 'radiate' the heat straight at you (and the surounding walls furniture), which in turn heat faster.  We 'feel' that heat on our skin/face etc and it makes us 'feel' cosy and warm.  Whereas a white central heating radiator (Ha!) radiates virtually nothing, especially when its hidden behind the couch, and warms the air in the room (slowly) which convects around the place(can lead to drafts) and doesn't necessarily make the occupant 'feel' warm.  Stone walls will still feel cold to the touch, and thus an occupant can 'feel' cold as heat radiate from them, out to the walls.

 

[cavemanmike]

You do like a rant don't you Sam 

 

[ChrisJC]

Just as an aside - can everyone stop using the word 'efficient'  incorrectly.   

Are we allowed to say that the woodburner is much more efficient than an open fire?

And out of curiosity, are they more or less efficient than a gas or oil boiler?

Chris.

 

[pwhole]

My physics teacher at school used to regularly rant that if everyone painted their radiators matt black instead of gloss white, they would be so much more efficient. Anyway, I have central heating, and it takes 15 minutes to warm up my entire (2 bedroom) flat for about three hours before it's noticeably chilled off. And I have the window open much of the time when I'm smoking. I just put a jumper on if I'm cold. The last winter quarter gas bill (Jan-April) was ?72.19, and that also includes all my cooking and all my hot water. Between April and October I never have the heating on as it's too warm.

 

[SamT]

You do like a rant don't you Sam 

Are we allowed to say that the woodburner is much more efficient than an open fire?
Chris.

Yes, much.

And out of curiosity, are they more or less efficient than a gas or oil boiler?

Oil boiler ~ 90%
Mains Gas ~89%
Log burner ~65% (some manufacturers have claims about 80%, but always good to be skeptical) 
Open fire ~40%

 

[cavemanmike]

What about bio - lpg

 

[SamT]

"Bio LPG" is a contradiction of terms, unless you're talking about two separate things,.

LPG stands for Liquid Petroleum Gas.  Its essentially butane/propane, either straight from the ground, or as a byproduct of oil refraction.  In a modern boiler, its about 90% efficient.  Its a fossil fuel and not 'bio'.

(I think its slightly higher efficiency than Mains gas (90/91% vs 89%) , because I suspect its got a higher humidity content than Mains Gas, which means in a condensing boiler, the condensing technology of it squeezes a tad more energy out of it).  (but I could be wrong on that)

Bio gas, is methane, usually captured from digestion (composting).  I expect that in a condensing boiler, it'd be about 90% give or take.

If you want to take into account primary energy efficiency, i.e. the energy it takes to get it to the point of use, from digging it out the ground, we're into a whole different kettle of fish.

 

[SamT]

Beechwood fires are bright and clear
If the logs are kept a year,
Chestnut?s only good they say,
If for logs ?tis laid away.

Make a fire of Elder tree,
Death within your house will be;
But ash new or ash old,
Is fit for a queen with crown of gold.

Birch and fir logs burn too fast
Blaze up bright and do not last,
it is by the Irish said
Hawthorn bakes the sweetest bread.
Elm wood burns like churchyard mould,
E?en the very flames are cold
But ash green or ash brown
Is fit for a queen with golden crown

Poplar gives a bitter smoke,
Fills your eyes and makes you choke,
Apple wood will scent your room
Pear wood smells like flowers in bloom

Oaken logs, if dry and old
keep away the winter?s cold
But ash wet or ash dry
a king shall warm his slippers by.

 

[mr conners]

MDF, if it is free
Chuck it on,
and warm you?ll be.

 

[owd git]

https://youtu.be/h7HiPFnyoac

 

[cavemanmike]

https://www.liquidgasuk.org/about/biolpg

 

[SamT]

Yeah.. fair enough, Daft name though.  You'd have thought they'd want to drop the "petroleum" bit and distance themselves from the fossil fuel industry.

Its still going to be 90% odd efficient in a condensing boiler is its just Butane/Propane.

Problem is supply,  how much agricultural land are you going to give over, away from food production, to grow crops for biogas.

The topic probably needs a new split if we're going off on a 'renewables' tangent.

 

[cavemanmike]

There probably importing the stuff which doesn't make it very green

 

[ChrisJC]

Problem is supply,  how much agricultural land are you going to give over, away from food production, to grow crops for biogas.

And do they factor in all the Diesel burned by the farmer producing the crops...?

Chris.