Homemade Stoves

[SteamyTea]

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

[joe90]

1 hour ago, SteamyTea said:

This is why the advice is to burn fiercely for a short time. 

And I think this is why rocket stoves “appear” to be effective, very hot burn. I do fancy making one to heat my garage when I have to work out there (and I have loads of timber offcuts from my wood shop and a forest on my doorstep with fallen timber.) plus I love making stuff.

[G and J]

5 minutes ago, joe90 said:

And I think this is why rocket stoves “appear” to be effective, very hot burn. I do fancy making one to heat my garage when I have to work out there (and I have loads of timber offcuts from my wood shop and a forest on my doorstep with fallen timber.) plus I love making stuff.

Good plan.  Don’t forget the armchair and side table next to said woodburner. Oh and the stovetop kettle.  And maybe a few snacks.  And how about a TV on the wall on the left…..

[ProDave]

And your slippers and your pipe.......

[joe90]

1 minute ago, G and J said:

Good plan.  Don’t forget the armchair and side table next to said woodburner. Oh and the stovetop kettle.  And maybe a few snacks.  And how about a TV on the wall on the left…..

Sorry no room, it’s full of bikes that are mid re build and other projects

[joe90]

3 minutes ago, ProDave said:

And your slippers and your pipe.......

They are in the snug. (Sorry steamy).

Edited January 5 by joe90

[G and J]

7 minutes ago, joe90 said:

Sorry no room, it’s full of bikes that are mid re build and other projects

That can’t be a workshop - there’s some floor showing!

[joe90]

5 minutes ago, G and J said:

That can’t be a workshop - there’s some floor showing!

Not a lot (you can’t see the other side 🤷‍♂️)

[Roger440]

As rants go, not your best. 5/10

 

However, id imagine we will see more of this, as well as more "proper" stoves, once either, there are rolling blackouts, or the remote control of heat pumps is implemented.

 

Im not everyone else, but i really, really dont like being cold. Going solely electric for heating puts me at the mercy of Ed and chums. I will not be part of that experiment, nor a victim.

 

Add in to the above, ever increasing elecricity costs, means that people will use alternatives.

 

Despite being in the "no wood burner" camp, im having to reconsider that position for my barn, especially as im surrounded by free wood. A combined system of oil and wood is probably my best option, with just oil and a bit of solar for the house. Which leaves me independant of the grid for heat.

 

4/10?

 

[Roger440]

17 minutes ago, joe90 said:

Sorry no room, it’s full of bikes that are mid re build and other projects

 

I like the picture of the petrol pump rather than a real one. Very cost effective.

 

Im still looking for a cheap one, because i want to actually dispense tractor food from it. But there are no cheap ones.

[G and J]

1 minute ago, Roger440 said:

As rants go, not your best. 5/10

I’m sorry.  I must rant harder.  
 

(And I am green tinged really, our current house has an oil boiler, a bottled gas hob, and three wood burners and the new one will have an ASHP and only one woodburner and we are debating whether to have a permanent or portable induction hob).

[Roger440]

1 minute ago, G and J said:

I’m sorry.  I must rant harder.  
 

(And I am green tinged really, our current house has an oil boiler, a bottled gas hob, and three wood burners and the new one will have an ASHP and only one woodburner and we are debating whether to have a permanent or portable induction hob).

 

Sorry, was aimed at Steamy.

 

[G and J]

1 minute ago, Roger440 said:

 

I like the picture of the petrol pump rather than a real one. Very cost effective.

 

Im still looking for a cheap one, because i want to actually dispense tractor food from it. But there are no cheap ones.

That’s a petrol pump for an e-bike, you can see the 13a socket by the side.

[Roger440]

1 minute ago, G and J said:

I’m sorry.  I must rant harder.  
 

(And I am green tinged really, our current house has an oil boiler, a bottled gas hob, and three wood burners and the new one will have an ASHP and only one woodburner and we are debating whether to have a permanent or portable induction hob).

 

I just want to be warm, as cheaply as possible. Therefore electricity is excluded on cost alone, before we consider future costs and stability of supply.

[SteamyTea]

49 minutes ago, joe90 said:

Those Numatics are mean suckers.

Tried to do the restaurant carpet with one (410m²), nearly killed me.

Went to buy a new vacuum for home yesterday as I bust my 20 year sold Hoover at work.  Curries had been broken into, so nothing till Wednesday.

 

37 minutes ago, Roger440 said:

Despite being in the "no wood burner" camp, im having to reconsider that position for my barn, especially as im surrounded by free wood. A combined system of oil and wood is probably my best option, with just oil and a bit of solar for the house. Which leaves me independant of the grid for heat.

Then my comments about fitting it outside may be useful.

Wood pellets are about 12p/kWh once delivery, VAT and efficiency is taken into account.  Which is about the same as I pay for my E7 night rate.

32 minutes ago, Roger440 said:

Therefore electricity is excluded on cost alone

Except that electricity prices are artificially high because they are based on gas prices.  This could change, and must change, if we are to tackle climate change, especially if around 70% of our generation is now low carbon.  It is wrong to blame renewable energy on high prices.  It is now the cheapest form of electricity.

[joe90]

3 minutes ago, SteamyTea said:

Those Numatics are mean suckers.

Tried to do the restaurant carpet with one (410m²), nearly killed me.

In the house I have a re chargeable shark which does a great job and very light but may not last for a large area. The numatic is great for the workshop and dog hairs in the car.

[ToughButterCup]

32 minutes ago, Roger440 said:

... Therefore electricity is excluded on cost alone,....

 

'Therefore'  is a dangerous word.

You have three wood burners. Those burners need to be supplied with wood. And the house needs additional cleaning   - smoke produces dust, oils, 

 

How much do you pay someone (a teenager?)  to gather, fetch, stack, chop, restack, supply the fire? How much did your log-store(s) cost to put up and maintain?

How much do you pay a cleaner to cope with the after-effects of burning fuel on a wood burner?

How much do you pay someone to empty the ash from the fire ?

 

Are those costs currently hidden by family good-will?

 

I merely point out that mis-applied,  the word 'therefore' sometimes hides assumptions. 

I would love three log burners: I love the work associated with a fire. But one day (soon), I won't be able to manage that process. But at least until then in our house , I could have every door open all day and all night 

[SteamyTea]

8 minutes ago, joe90 said:

In the house I have a re chargeable shark which does a great job and very light

Getting a corded Shark for home, it is lighter than the rechargeable ones.

They are good vacuums, but I know from experience that we would get though 4 a year at work, because we have just replaced, for the third time, the work Shark in 8 months.  Sooner or later they will stop replacing them under the 5 year warrantee (which has another 4 and a bit years to run).

[ProDave]

32 minutes ago, SteamyTea said:

Curries had been broken into, so nothing till Wednesday.

the thieves got clean away.......

[G and J]

4 minutes ago, ProDave said:

the thieves got clean away.......

Did they hoover out the place?

[G and J]

1 hour ago, Roger440 said:

Therefore electricity is excluded on cost alone

Ummm, with an ASHP with a decent COP lecky will beat gas just about methinks, especially if one factors in servicing.  
 

Oil is still wonderfully cheap, but requires annual servicing and space for storage and deliveries and methinks will soon-ish be targeted to push peeps towards lecky just for political boxticking if nothing else.

 

So, I think given best guesses re future price trends lecky wins.  So there.  Or rather, so not therefore…

[joe90]

2 minutes ago, G and J said:

with an ASHP with a decent COP lecky will beat gas just about methinks, especially if one factors in servicing.  

And standing charges.

[G and J]

33 minutes ago, ToughButterCup said:

How much do you pay someone (a teenager?)  to gather, fetch, stack, chop, restack, supply the fire? How much did your log-store(s) cost to put up and maintain?

I used to do that all myself but got lazy and lost my workbuddy so now I pay a professional who does it properly, with no modern slavery required.

 

34 minutes ago, ToughButterCup said:

How much do you pay a cleaner to cope with the after-effects of burning fuel on a wood burner?

I don’t charge for my time.

 

35 minutes ago, ToughButterCup said:

How much do you pay someone to empty the ash from the fire ?

Honestly, I really don’t charge for my time.

 

36 minutes ago, ToughButterCup said:

I could have every door open all day and all night 

We only have one on at once except anon Christmas Day, the rest of the time walking to another part of the house is bracing like one of those refreshing ice baths the Scandinorwegilanders take after a sauna.  They must be bloody mad lol

 

 

[G and J]

3 minutes ago, joe90 said:

And standing charges.

I don’t charge for my time standing up either.  I’m cheap, me.

[Onoff]

4 hours ago, 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.

 

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.