Homemade Stoves

[joe90]

8 minutes ago, markocosic said:

Not buying it as the 'ultimate' option.

Oh I agree in reality, 

10 minutes ago, markocosic said:

Spark ignition CHP running on methane from the cow shed / naerobic digestion plant plus syngas from wood gasification.

No cows and ,”the other stuff”

12 minutes ago, markocosic said:

PV for offsetting demand for fuel entirely.

Most definitely 

[Onoff]

Say you had unlimited access to the waste steam of 60 cattle. I know someone who has who otherwise struggles with fuel poverty. Can't help thinking that's an untapped resource. 

 

Just don't how you'd go about tapping it. 

 

 

[joe90]

2 minutes ago, Jilly said:

What about biogas? I know of people who have constructed homemade bio digesters which run off compost and animal poop. I’m sure it’s not perfect, but has fewer downsides than wood burning. 

All these options have up sides and down sides, most people would not entertain any of them but I find it all very interesting, from straw bale construction which I was interested in 30 years ago through self generated lekky to home made diesel. And, the start of this thread (which I am sorry to have miss directed) home made stoves and a rocket stove which I might make for my workshop just because I can. Yes biogas is yet another alternative but you need either the animals, compost or other “fuel” to run it so that would depend on your lifestyle. 

[Jilly]

27 minutes ago, Onoff said:

Say you had unlimited access to the waste steam of 60 cattle. I know someone who has who otherwise struggles with fuel poverty. Can't help thinking that's an untapped resource. 

 

Just don't how you'd go about tapping it. 

 

 

Look up Biff the Biodigester

[joe90]

33 minutes ago, Onoff said:

Just don't how you'd go about tapping it. 

Requires money up front to buy the kit to harvest the “fuel” and if she is struggling with fuel poverty how would she afford the kit?

 

[SteamyTea]

Large dairy farms already collect waste and process it into methane, that is then injected into the gas grid.

It is not as simple as putting it into a container, letting it rot, and piping the gas away.

Below is an example of a small scale one in India.

https://www.biocycle.net/india-dairy-farmers-install-small-scale-digesters/

Note that they are claiming carbon credits, which is often the main income from them.

 

There were a couple of conmen based in Devon that convinced someone on the Green Building Forum to buy their unproven design.  All it was was an underground storage cylinder connected inline with the household sewage.  They claimed more energy out than in.

I went to see them, on the insistence of Viking House's Seamus and the Architect Tom Foster.

The whole setup was a farce.

7 hours of my life I will never get back.

 

Just followed a link in the Indian Article to a smaller bio-digester.

https://www.biocycle.net/food-waste-to-biofertilizer-using-home-digesters/

 

Edited Wednesday at 05:09 by SteamyTea

[Onoff]

5 hours ago, joe90 said:

Requires money up front to buy the kit to harvest the “fuel” and if she is struggling with fuel poverty how would she afford the kit?

 

 

I was more thinking IBC tanks...

 

I know, 100% that bio gas is* a huge thing in Nepal. Both the Gurkhas engineers (late 50s, early 60s) I work with say about their mum's feeding a few shovels of buffalo dung into an underground, domed tank each day. They would cook with the resultant, piped gas and do their homework by gaslight.

 

https://www.build-a-biogas-plant.com/PDF/NepalBiogasPlant.pdf

 

I say is, as more recently there has been a state sponsored move to run electrical supplies to properties. Apparently you get a connection box on your property whether you like it or not and are charged. 

 

It's all about control I guess, taking the power away from the people 😉

Edited Wednesday at 05:22 by Onoff

[SteamyTea]

31 minutes ago, Onoff said:

It's all about control I guess, taking the power away from the people

Another way to think of it is that the government is improving people's quality of life as Nepal moves towards full democracy.

(I know nothing about Nepal except the best 'Indian' restaurant I have found in Penzance is seems to have some connection to Joanna Lumley, and that is good enough for me)

[Onoff]

18 minutes ago, SteamyTea said:

Another way to think of it is that the government is improving people's quality of life as Nepal moves towards full democracy.

 

Poor sods, they'll have heat pumps foisted upon them next before they get windows and doors! 

[MikeSharp01]

On 05/01/2025 at 08:28, SteamyTea said:

even though we all hate legislation

Rule of law is a good thing in a liberal democracy perhaps not so much in an authoritarian regime I agree - but we are not there yet. Poorly formed laws that pay no pre-emptive attention to unintended consequences should be challenged.

[markocosic]

9 hours ago, Onoff said:

Say you had unlimited access to the waste steam of 60 cattle. I know someone who has who otherwise struggles with fuel poverty. Can't help thinking that's an untapped resource. 

 

Just don't how you'd go about tapping it. 

 

 

 

You build traditional balkan houses.

 

Ground floor? Where you overnight then pigs/cows/sheep in winter. 

 

First floor? Where you overnight then humans for most of the winter. 

 

The solution need not be sophisticated.

 

You have more choices in the UK though. There isn't a real winter. There are plenty of economic opportunities should you choose to follow these rather than following passions.

[markocosic]

9 hours ago, Roger440 said:

 

And near enough (as can be achieved) government proof. And cheaper. Well so long as i dont run the genny outside of power cuts. Sadly seen a lot of use lately. I think 7 since november. Including one over 48 hours. 

 

And you wonder why i posted what i did?

 

Agree that it's upfront easy.

 

It's just efficiency ugly is all.

[LnP]

On 05/01/2025 at 08:28, SteamyTea said:

As usual, when the weather gets chilly, people start to think of getting a wood burning stove and extracting as much energy out of it as possible.

Now there are many reasons to not use a WBS which are well documented on here, and it seems to me there is only one reason to have them.

But regardless of all that, my concern is that people think they can successfully make their own, or modify existing ones.

 

A bit of physics.

When a carbon based fuel is combusted in air, there is a rapid rise in temperature as the carbon atoms in the fuel (usually a molecule of carbon, hydrogen and other trace elements) combine with the oxygen in the air mixture (around 21% oxygen, 78% nitrogen, 1% argon and traces of the rest).  This mainly produces carbon dioxide, some water vapour and a lot of nitrogen.

Because these gases are at a high temperature, they have a lower density than the surrounding air, so rise up the flue and are expelled to the atmosphere.

 

What really happens.

As a combustion process is not 100% efficient, temperature is not even, the fuel is not homogenous (randomly lumpy) and the airflow is turbulent, many other chemical reactions take place.

There are three reactions to be wary of.

Carbon Monoxide.  This is a killer.  Now many things produce CO, car exhausts being a major concern.  A modern car produces about 5-15 ppmv (parts per million by volume), and WBS 5000 ppmv.  The LC₅₀ number (lethal concentration to kill 50%) is 3614ppm.

Nitrogen Dioxide has an LC₅₀ of 176, this does not seem particularly high.  The problem is that NO₂ is a secondary by-product that is created from nitric oxide (NO, aka NOX).  This gas has an LC₅₀ of 1739.

Then there are the PM10 and PM2.5 particulates.  This is a huge problem with about 22% of the total emissions coming from domestic stoves and fires.  There is a lot of nonsense spoken about them i.e. the levels where higher in the past (when people frequently died from heart attacks in their 40s) to "I only use properly dried timber" (particulates can form after combustion though chemical reactions), and my favourite "I live in the countryside" (as if there are no pollution problems there).

 

A problem when extracting energy.

As a rule, you cannot extract all the energy from combustion, entropy (a fascinating subject) does not allow it.

With thermal combustion, and especially with small domestic burners, the incoming air is at a higher density than the outgoing gases (they are not as as we think of it any more).  This difference is created by the higher temperature in the grate and is what 'draws the gases up the flue'.  Energy is effectively extracted from these gases after the combustion process has taken place (though there is a small radiative effect from the points of combustion).

If too much energy is removed, the difference between the incoming air and the outgoing gases temperatures, and therefore density, is reduced.  This stalls the airflow though the combustible material, creating more pollutants. This is why the advice is to burn fiercely for a short time.  This does not happen in reality though.  The initial period of combustion is slow (maybe an hour) and the tail end is slower still (grate is still warm in the morning), maybe several hours.  This means that optimum combustion times are very short, and the more energy extracted, the longer the partial combustion periods are.

 

Concluding.

There are many DIY stove designs available, then someone comes along and suggests adding a water jacket to heat water, adding mass around the stove increases the efficiency (it does not), then someone else suggests that more energy can be extracted from the 'waste' flue gases ("my exhaust temperature is only 26°C, how good is that").  These are, without proper understanding and design (which generally does not come from a bearded sage on the internet) potentially deadly heating equipment.

So if you really must, usually for vanity purposes, fit a WBS, get a properly designed and built one, fitted correctly (even though we all hate legislation), maintained properly (we spend hundreds doing that to our cars, and are thankful that aeroplanes are services), use only small amounts of timber, that is properly dried (not just one end and assume the fire will dry the rest out).

I have suggested in the past that WBS could be fitted though the wall, with a sealed window on the inside.  You get your focal point but all the shit is kept outside for the rest of us to enjoy.  It is a similar idea to fitting out ASHPs, PV modules and Wind Turbines outside

On the subject of wood burning stoves and health and safety, be sure to follow the guidance on separation from combustible materials. I have a relative in Canada whose house burnt down because his stove was too close to some wood panelling. The radiant heat from the stove raised the temperature of the wood above its autoignition temperature and it ignited. Autoignition - you don't need a spark or a flame, just get it hot enough and it will burst into flames, like a chip pan fire.

[ProDave]

4 minutes ago, LnP said:

The radiant heat from the stove raised the temperature of the wood above its autoignition temperature and it ignited. Autoignition - you don't need a spark or a flame, just get it hot enough and it will burst into flames, like a chip pan fire.

Distance to flammable materials was one aspect that BC checked meticulously on their final inspection.

[sgt_woulds]

Back to the original subject, and regarding the efficiency of the wood burn, (which requires a short, high temperature burn) and the need to remove the combustion process from the internal environment I agree that Iron WB stoves are a non-starter and definitely shouldn't be DIY modified.

 

So we should be installing masonry stoves, (Kachelofen, steinofen, pystyuuni, kakelugn, other names depending on where you are in the world) all of which are easily DIY-able - although the best ones with special ceramic burn chambers and venturi ventilation to boost burn temperatures above 2000°C do require special components. 

 

Most of the ones I've seen and used in Hungary had external firing chambers for easy loading and cleaning.  Some did have a window inside where you could see the flames but as the burn typically lasts less than 60 to 90 minutes it's not worthwhile.

 

Even the most basic designs will effectively use faggots of thin sticks, (not inefficient logs), leave very little ash and produce very low waste gases and particulates, (and low-temperature exhaust) from the chimney.  They have efficiencies heading towards 90%.

 

I have looked in the inspection holes and there doesn't appear to be any tar or other deposits in the chimney and I'm told they rarely need cleaning unless wet fuel or logs are used.

 

Rocket stoves, a combination of a fire barrel, flue and cob - are a poor relation masonry stoves - but are quicker, easier, and cheaper to build.  I don't have experience with them, but some say the indoor air is less pleasant due to dust scorching on the barrel, similar to modern iron stoves.

 

I have lived with an iron WBS and although the sight of a simmering fire was soothing on a dark evening, that was pretty much the only plus point I could see.

 

A true masonry stove produces low-temperature radiant heat, and many have in-built seats or day beds so you can snuggle right up.

 

In the depths of winter, our relatives fire their stove twice a day, using two faggots at a time.  In the shoulder months, 1 burn a day is sufficient.

 

 

[Wil]

Any images of these masonry stoves? I’d love to incorporate a masonry stove in our renovations (especially if my existing inglenook could be repurposed…)

[markocosic]

7 hours ago, ProDave said:

Distance to flammable materials was one aspect that BC checked meticulously on their final inspection.

 

I set fire to a dark towel over the back of a chair placed over a metre from the fire when using it for the first time.

 

Sub 200C double walled convection stove it might be. Doesn't prevent numpty from lighting it up, arranging their wedding shoes and towel a comfortable distance from it at startup temperatures, then coming back 15 minutes later to a secondary fire from the radiant heat!

[Beau]

1 hour ago, Wil said:

Any images of these masonry stoves? I’d love to incorporate a masonry stove in our renovations (especially if my existing inglenook could be repurposed…)

I saw  this firm https://www.cornishmasonrystoves.com/about-us  selling custom masonry stoves at the Royal Cornwall show a few years back. 

 

 

[SteamyTea]

22 minutes ago, markocosic said:

I set fire to a dark towel over the back of a chair

What were the particulate emissions?

[Beau]

Not really a stove but it does burn logs.

 

My home made charcoal retort with the lid up. Had one of these up to 900C which was a tad exciting!

 

 

Edited Wednesday at 17:31 by Beau

[ProDave]

41 minutes ago, markocosic said:

 

I set fire to a dark towel over the back of a chair placed over a metre from the fire when using it for the first time.

 

Sub 200C double walled convection stove it might be. Doesn't prevent numpty from lighting it up, arranging their wedding shoes and towel a comfortable distance from it at startup temperatures, then coming back 15 minutes later to a secondary fire from the radiant heat!

Ours is also a convection stove and has very small distance to combustibles figures from the back and the sides of the stove.

 

But the front is a normal door, with a large glass window, and that is just like any other stove, it radiates a LOT of heat and not at all surprising it could set fire to something with a low flash point close to it.

 

Oddly enough there seems to be no requirement to publish a "distance to combustibles" figure for the front of a stove.

[SteamyTea]

2 hours ago, Beau said:

Had one of these up to 900C which was a tad exciting

A good laugh as it will have produced so N₂O.

[LnP]

14 hours ago, ProDave said:

 

But the front is a normal door, with a large glass window, and that is just like any other stove, it radiates a LOT of heat and not at all surprising it could set fire to something with a low flash point close to it.

 

It's not the flash point you you have to think about, it's the autoignition temperature. They're not the same.

 

Flash point is the temperature you have to heat something to so that when you hold a naked flame over it, the vapours coming off it will ignite. As you raise the temperature, the concentration of the vapours in air increases until it gets to the lower flammable limit and a flame will ignite them. Autoignition is the temperature you have to heat something to so that it ignites without the presence of a naked flame.

 

Not being pedantic, just want to highlight that it wasn't a naked flame which caused markocosic's towel to catch fire. It just got too hot.

[SteamyTea]

1 hour ago, LnP said:

It's not the flash point you you have to think about, it's the autoignition temperature

Yes, they are different, and different between, what seems on the face of it, similar 'fuels'.

 

Gasolene and diesel may seem similar.

Gasolene has a flash point of -42.8°C and an autoignition temperature of 246 to 280°C.

Diesel has a flash point of 37.8 to 65.6°C and an autoignition temperature of 210°C.

 

(those temperatures can vary depending on the blend)

[sgt_woulds]

The flammable vapours released might also play a part depending upon distance and the presence of exposed flames.

 

I used to work on the Goodyear blimp.  Once, in France, we had an Avgas spillage - about 80 - 100 litres. 

 

I can't remember which airport it was, but it was a fairly major one and their response was extraordinary.  They closed the airport and evacuated an enormous area down-wind of the spillage, (at least half a km.  Mostly fields although they had to ask a farmer to switch off his tractor and put out his cigarette - for a French farmer this must have been like asking him to chop part of his face off!)  

 

Within 15 minutes a team of engineers, diggers, and lorries had arrived, excavated the site of the spillage down to a depth of about 2m and a diameter of about 6m and carted the offending material away.  A new team arrived on their heels, filled the hole and laid new turf.

 

All in the whole process took less than one hour from when we reported the spillage to the tower!

 

Seems extreme, but the incident team leader, (possibly the angriest chap I've ever met -quite an achievement as the French are good at simmering resentment) said that another airport in France had had an Avgas fire and the ignition source was outside the airfield boundary!