Wood burning stoves tested to destruction

[Spectric]

Many bends?

According to HETAS you are only allowed a maximum of four and there is a limit on what percentage of total flue length is not vertical.

Here is something to think about, the whole objective of having a woodburner is to produce heat to warm your house, so having a length of single wall flue pipe from the stove to the twin wall makes more sense than twin wall all the way to the stove as the single wall pipe will radiate heat. Now older stoves were just cast iron with no firebricks so providing you have no flamable materials nearby the whole stove gets hot and radiates heat. We now have firebricks which seem to me to be about keeping the heat in the stove and keeping the outer surfaces cooler, why if there is only bricks and mortar nearby which will not burn.

 

[Jacob]

..... We now have firebricks which seem to me to be about keeping the heat in the stove and keeping the outer surfaces cooler, why if there is only bricks and mortar nearby which will not burn.

Thermal shock with cast iron. Has to heat up more slowly than steel, so I'm told.
Even without bricks many CI stoves have baffles of various sorts, which burn out and have to be replaced.

 

[Spectric]

Ok so lets replace the cast iron with steel plate, so now why the firebricks ?

 

[Jacob]

Ok so lets replace the cast iron with steel plate, so now why the firebricks ?

Exactly. The Dowlings don't have fire bricks and heat up faster. Might sound like a trivial detail but the fast heat-up saves fuel, especially if you just need a quick blast.

 

[Krome10]

@Spectric - I agree RE the flue. But some people I've spoken to, including installers and stove shop owners, say the opposite and stress the importance of double skinned flue all the way, especially for ED stoves. not saying that's what I think, just sharing what some have told me.

With regards the fire brick issue, I think this was discussed earlier in the thread. I must admit, I still don't feel like there's a clear answer on that. I can see the logic that the hotter the stove body gets, the more heat will radiate. So no bricks is better because the stove gets hotter. But heat is heat, right? So unless the claim is that the heat from stoves with fire bricks is going up the chimney, I can't make sense of the argument. That heat has to go to room one way or another. Modern stoves mostly claim 80%+ efficiency. Burley stoves claim 90%+. Not sure about Dowling, but guess they'll be around the same or lower. So the heat can't be getting "lost" by having fire bricks, can it? Which then begs the question of where and how that heat eminates. My guess would the the glass. Not sure what temps that can reach compared to steel / CI. It would also lend to the idea that the fire bricks (and baffle) are designed to push the heat out the front of the stove.

If I'm missing something - which I most likely am - I look forward to hearing what!

This does touch on something that baffled (pun intended) me when we bought our stove a few years back... In the manual it said maximum stove body temp 230c. Some stoves are significantly higher. So how can they then be assessed to have the same heat output? Never got a direct answer; the best I got then was also that the glass plays a big part....

 

[Spectric]

But some people I've spoken to, including installers and stove shop owners, say the opposite and stress the importance of double skinned flue all the way,

The installers I used said it is better to have single wall from the stove to get more radiated heat providing certain conditions are met. One of those is that if it is within an existing fireplace and there is a wooden mantel that can be a problem which twin wall overcomes or you cannot meet the required clearance for using single wall.

The Dowlings don't have fire bricks and heat up faster.

Which is logical so are we seeing firebricks used because of clearances around stoves and many being used free standing in newer homes using these heat shields rather than having a solid masonary wall.

The thing that baffles me is how we now have DEFRA approved stoves for smoke free areas, so do these types of stove burn hotter to reduce smoke because burning wood must create smoke.

 

[Krome10]

The thing that baffles me is how we now have DEFRA approved stoves for smoke free areas, so do these types of stove burn hotter to reduce smoke because burning wood must create smoke.

AFAIK, the whole DEFRA thing is a stopper which prevents the stoves being able to be closed down too far, i.e. to slumber or "keep-in" overnight. On many stoves the stopper is simply a screw or bolt which can be removed, which makes a mockery of it anyway...

 

[Spectric]

So what is this stopper, I assume it prevents you turning the air right down. So for years people have stacked there fires to keep them going overnight ready for the next morning, this sounds much like the start / stop used on vehicles where they can no longer idle.

 

[Krome10]

Yeah, I guess the analogy works to a certain extent, but I think it's also about the efficiency and emissions... Compare what comes out of the chimney of a fire/stove being started or ticking over, with one running at optimal efficiency...

 

[Jacob]

.... So for years people have stacked their fires to keep them going overnight ready for the next morning, ....

Sort of traditional - hence termed "log" burner rather than "any old wood" burner.
Not really necessary in our mild climate and fire-going-out followed by a quick-startup makes more sense to me. Cleaner too - slow smouldering fire also means more soot and tar in the chimney.
If you look at peasant wood stoves in Russia where they are absolutely essential, they aren't particularly "log" burners either, but use fast burn small stuff (birch etc) and have huge masonry mass as heat reservoir for the cold nights.

 

[Fergie 307]

The installers I used said it is better to have single wall from the stove to get more radiated heat providing certain conditions are met. One of those is that if it is within an existing fireplace and there is a wooden mantel that can be a problem which twin wall overcomes or you cannot meet the required clearance for using single wall.


Which is logical so are we seeing firebricks used because of clearances around stoves and many being used free standing in newer homes using these heat shields rather than having a solid masonary wall.

The thing that baffles me is how we now have DEFRA approved stoves for smoke free areas, so do these types of stove burn hotter to reduce smoke because burning wood must create smoke.

We have a purely decorative oak mantle, and we're concerned about this. We have a plate of stainless steel inside the opening to shield it from the heat. It is not visible unless you crawl about on the floor.

 

[Spectric]

Two ways to look at what are now thought of as potential issues with solid fuel burners. Are we just being way over cautious or were our ancestors being naive. Open fires were once the main means for people to keep their homes warm and having a wooden mantel was probably for the majority with only the wealthy having a stone surround, plus a lot of these homes were also thatched so were houses burning down common ?

Then today we have these holiday tents that have a woodburner fitted, yes a woodburner in a canvas building so maybe we are being far too cautious when it comes to the regulations about solid fuel installations. One thing they come up with is something called pyrolysis where the ignition point of an organic material such as wood will reduce over time if it is overheated and does not need oxygen present which sounds like the process for making charcoal which burns well !

Another issue might be that modern homes are built like fancy sheds with cheap stud walls and minimal brick walls so they pose a higher risk if woodburners are fitted and are too close to a stud wall because plasterboard is not fire proof, not even the pink stuff is A1 rated. When it comes to heat shields just having a metal plate on a wall will not prevent the heat from passing into the wall, a proper heat shield will be spaced away from the wall so there is airflow between it and the wall so this acts likes a barrier.

 

[Fergie 307]

Our concern was primarily that it is oiled, and whether the heat would cause it to start dripping oil.

 

[Glenhyrst]

We have a cast iron Jotul woodburner that we have had for years. Chosen entirely on looks by my wife and does a good job. Can get as hot as hell and have you pinned against the far wall trying to keep cool. What troubles me is that as yet, I've seen no detrimental signs of this much mentioned "thermal shock". What am I doing wrong?

 

[Jacob]

We have a cast iron Jotul woodburner that we have had for years. Chosen entirely on looks by my wife and does a good job. Can get as hot as hell and have you pinned against the far wall trying to keep cool. What troubles me is that as yet, I've seen no detrimental signs of this much mentioned "thermal shock". What am I doing wrong?

it's rapid heat up from cold which can be a problem, I'm told. The advice with a lot of modern stoves is to warm them up carefully rather than opening it up for a full blast. My only experience with this was with a Morso Squirrel, which seemed to need new bricks and baffles every year. Not cheap either.

 

[Glenhyrst]

Interesting and slow start up may be key. But had the beast for maybe 20years and never needed to replace anything at all. I used to like damping it down at bedtime and felt like I'd secured a victory when it restarted in the morning on just opening the "vent". And was still warm.
Now more aware of need to run it at a higher temperature for a more effecient and less polluting burn. So a fresh light up every morning.

 

[BC'er]

The Dowling stoves look like the crude stuff that was welded up in North America in the late 60s and early 70s when the wood stove "movement" was just getting going. Fit to stick in a shed or basement corner I suppose, but in a living space? No thanks.

The ultimate in fuel-consumed to heat-felt is the Russian or Scandinavian "Masonry heater" which extract most of the heat from the flue gasses- where the most heat is lost - before venting outside. As I expect we all know, such heaters were built into the houses, often in the centre of the building and even included sleeping platforms in previous generations.

I had a look at Dowling's videos: nothing of substance I can see, just superficial amusements. If one face of the "pyramid" lifts up to load the stove, a very high draft will be needed to keep smoke from billowing out into the room as there is no space to contain it with the typical "diving bell effect".

There is a trade-off between the speed heat is transmitted to the surrounding room and the need to maintain high combustion temperatures for both maximum heat output and completeness of combustion. Firebrick contains heat and it could be said reflects it back into the combustion space.

The same principle is visible in an open campfire: if your fire is loose and open with spaces between the logs that are too large, the heat at the core of the fire escapes too easily and combustion is slow and heat output is poor. Conversely a well built fire maintains a high core temperature because the heat is not allowed to escape too quickly or too easily.

Firebrick and a suitable fuel load for the size of the combustion space does the same. You can build and maintain an efficient small fire in a large firebox, but it needs frequent attention to maintain. A fire of the same size in a suitably smaller firebox will have it's core temperature maintained by the closer heat containment of the firebrick and burn hotter with less attention and adjustment.

Yes, firebrick takes time to heat up and transmit heat through to the steel or iron body of a stove, but it also holds and continues to transmit heat after the fire goes down, as with the typical masonry heater. Most steel bodied, brick lined stoves have direct exposure of the upper walls, or at least the tops to the flames and that is where most of the heat transfer to the room occurs and where air is typically blown over or past the heated steel.

The Dowling has not even the pretense of secondary combustion, so it will be both less efficient and more polluting than a stove that does. In fact a simple old rectangular cast iron two-hob "garbage burner", preferably with a water jacket would be much more useful and convenient.

 

[Phil Pascoe]

The Dowling stoves look like the crude stuff that was welded up in North America in the late 60s and early 70s when the wood stove "movement" was just getting going. Fit to stick in a shed or basement corner I suppose, but in a living space? No thanks.

The ultimate in fuel-consumed to heat-felt is the Russian or Scandinavian "Masonry heater" which extract most of the heat from the flue gasses- where the most heat is lost - before venting outside. As I expect we all know, such heaters were built into the houses, often in the centre of the building and even included sleeping platforms in previous generations.

I had a look at Dowling's videos: nothing of substance I can see, just superficial amusements. If one face of the "pyramid" lifts up to load the stove, a very high draft will be needed to keep smoke from billowing out into the room as there is no space to contain it with the typical "diving bell effect".

There is a trade-off between the speed heat is transmitted to the surrounding room and the need to maintain high combustion temperatures for both maximum heat output and completeness of combustion. Firebrick contains heat and it could be said reflects it back into the combustion space.

The same principle is visible in an open campfire: if your fire is loose and open with spaces between the logs that are too large, the heat at the core of the fire escapes too easily and combustion is slow and heat output is poor. Conversely a well built fire maintains a high core temperature because the heat is not allowed to escape too quickly or too easily.

Firebrick and a suitable fuel load for the size of the combustion space does the same. You can build and maintain an efficient small fire in a large firebox, but it needs frequent attention to maintain. A fire of the same size in a suitably smaller firebox will have it's core temperature maintained by the closer heat containment of the firebrick and burn hotter with less attention and adjustment.

Yes, firebrick takes time to heat up and transmit heat through to the steel or iron body of a stove, but it also holds and continues to transmit heat after the fire goes down, as with the typical masonry heater. Most steel bodied, brick lined stoves have direct exposure of the upper walls, or at least the tops to the flames and that is where most of the heat transfer to the room occurs and where air is typically blown over or past the heated steel.

The Dowling has not even the pretense of secondary combustion, so it will be both less efficient and more polluting than a stove that does. In fact a simple old rectangular cast iron two-hob garbage burner", preferably with a water jacket would be much more useful and convenient.

The firebricks in the last stove I had (an expensive Clearview, I can't speak for others) were insulators - they stored next to nothing.
I wouldn't change my Dowling for anything else.

 

[Jacob]

The Dowling stoves look like the crude stuff that was welded up in North America in the late 60s and early 70s when the wood stove "movement" was just getting going. Fit to stick in a shed or basement corner I suppose, but in a living space? No thanks.

We've moved about a bit.
Had two in different living spaces during the last 20 years and they are brilliant.
Moved again, now installing a third.
I'll let you know how it goes.

 

[Cabinetman]

The Dowling stoves look like the crude stuff that was welded up in North America in the late 60s and early 70s when the wood stove "movement" was just getting going. Fit to stick in a shed or basement corner I suppose, but in a living space? No thanks.

The ultimate in fuel-consumed to heat-felt is the Russian or Scandinavian "Masonry heater" which extract most of the heat from the flue gasses- where the most heat is lost - before venting outside. As I expect we all know, such heaters were built into the houses, often in the centre of the building and even included sleeping platforms in previous generations.

I had a look at Dowling's videos: nothing of substance I can see, just superficial amusements. If one face of the "pyramid" lifts up to load the stove, a very high draft will be needed to keep smoke from billowing out into the room as there is no space to contain it with the typical "diving bell effect".

There is a trade-off between the speed heat is transmitted to the surrounding room and the need to maintain high combustion temperatures for both maximum heat output and completeness of combustion. Firebrick contains heat and it could be said reflects it back into the combustion space.

The same principle is visible in an open campfire: if your fire is loose and open with spaces between the logs that are too large, the heat at the core of the fire escapes too easily and combustion is slow and heat output is poor. Conversely a well built fire maintains a high core temperature because the heat is not allowed to escape too quickly or too easily.

Firebrick and a suitable fuel load for the size of the combustion space does the same. You can build and maintain an efficient small fire in a large firebox, but it needs frequent attention to maintain. A fire of the same size in a suitably smaller firebox will have it's core temperature maintained by the closer heat containment of the firebrick and burn hotter with less attention and adjustment.

Yes, firebrick takes time to heat up and transmit heat through to the steel or iron body of a stove, but it also holds and continues to transmit heat after the fire goes down, as with the typical masonry heater. Most steel bodied, brick lined stoves have direct exposure of the upper walls, or at least the tops to the flames and that is where most of the heat transfer to the room occurs and where air is typically blown over or past the heated steel.

The Dowling has not even the pretense of secondary combustion, so it will be both less efficient and more polluting than a stove that does. In fact a simple old rectangular cast iron two-hob "garbage burner", preferably with a water jacket would be much more useful and convenient.

Before this thread started I had thought fairly deeply about firebricks and not wanting them, but I must say you obviously know quite a bit about combustion, what you said about camp fires is certainly true.
I obviously hadn’t thought deeply enough as it hadn’t occurred to me that most of the heat comes out of the unbricked roof of the fire, time to get one of those fans I think.
Re the campfire thing. If I can’t work out a solution to a problem sometimes I stretch it to ridiculous lengths and the answer is usually staring at me, so with this, if all the logs were spread about with large gaps between its blindingly obvious that they would soon go out and the converse is that a very hot fire would be the outcome of well packed logs. So thank you for that.
Thing is as well, in the uk, we aren’t like the Russians with bitterly cold winters and certainly in my case the woodburner is for secondary heat and the deep satisfaction it provides burning away giving off a flickering light. Love them.
Ian