How do I know if my stove is multi-fuel.

[truckcab79]

The stove / woodburner on our boat is a small Helmsman.  Nobody in here seemed to know much about them and Google doesn’t help either.  
 

Until reading a thread on here I’d kind of worked on the assumption that ‘wood-burner’ was a sort of generic term and I could burn wood or coal but someone was being asked if theirs was multi-fuel.  Made me question mine. I’d just assumed I’d burn wood or smokeless fuel as I fancied.  Is there something that makes them able to only  burn one fuel type?  

[Guest]

2 minutes ago, truckcab79 said:

The stove / woodburner on our boat is a small Helmsman.  Nobody in here seemed to know much about them and Google doesn’t help either.  
 

Until reading a thread on here I’d kind of worked on the assumption that ‘wood-burner’ was a sort of generic term and I could burn wood or coal but someone was being asked if theirs was multi-fuel.  Made me question mine. I’d just assumed I’d burn wood or smokeless fuel as I fancied.  Is there something that makes them able to only  burn one fuel type?  

 

Multi fuel stoves normally have a riddle grate in the base.

[Alan de Enfield]

Multifuel stoves hhave a 'grid' in the base to allow ash to drop thru.

Woodburners just have a 'solid' plate for the fire to sit on.

[Jen-in-Wellies]

Wood burns best with air coming in from the top and likes having a bed of ash to burn on. The ash will rest either on a solid surface, or a grate with narrow gaps between the bars. Coals burn best with air coming in from underneath, so need a grate with reasonable gaps in the bars.

A multi fuel stove will have adjustable top and bottom air intakes and a compromise in grate bar spacing to suit both fuel types.

[Tony Brooks]

3 minutes ago, truckcab79 said:

The stove / woodburner on our boat is a small Helmsman.  Nobody in here seemed to know much about them and Google doesn’t help either.  
 

Until reading a thread on here I’d kind of worked on the assumption that ‘wood-burner’ was a sort of generic term and I could burn wood or coal but someone was being asked if theirs was multi-fuel.  Made me question mine. I’d just assumed I’d burn wood or smokeless fuel as I fancied.  Is there something that makes them able to only  burn one fuel type?  

 

Wood tends to burn best on a solid (non-ventilated) base with just top air while solid fuel burns best on a slotted/squared grate with mainly bottom air. Solid fuel stoves also tend to have firebricks or cast iron protection plates around the fire areas to protect the stove body from the extra heat.

 

So if you have a slotted grate and both top and bottom air controls with [potective firebrick/plates it is likely to be multi-fuel

[truckcab79]

46 minutes ago, Tony Brooks said:

 

Wood tends to burn best on a solid (non-ventilated) base with just top air while solid fuel burns best on a slotted/squared grate with mainly bottom air. Solid fuel stoves also tend to have firebricks or cast iron protection plates around the fire areas to protect the stove body from the extra heat.

 

So if you have a slotted grate and both top and bottom air controls with [potective firebrick/plates it is likely to be multi-fuel

Well I guess I’ll give either / both a go.  Have a look at my Springer build blog if you fancy another look but the grate was missing so I made my own slotted one.  There was a ledge for one to sit on.  There is only one controller and that’s at the bottom. There are fire bricks on the three internal sides. 

[Ianws]

5 hours ago, truckcab79 said:

Well I guess I’ll give either / both a go.  Have a look at my Springer build blog if you fancy another look but the grate was missing so I made my own slotted one.  There was a ledge for one to sit on.  There is only one controller and that’s at the bottom. There are fire bricks on the three internal sides. 

Sounds like a multifuel rather than a pur log burner. Log burners can have a bottom air control to help the fire start but once in the control is usually from the top air control. Multifuel fires are usually controlled by the bottom air control. The upper air control (where there is one) helps with secondary combustion and increases efficiency whilst reducing carbon on the stove glass. The grate ledge also suggests its a multifuel stove. 

[MrsM]

7 hours ago, Jen-in-Wellies said:

Wood burns best with air coming in from the top and likes having a bed of ash to burn on. The ash will rest either on a solid surface, or a grate with narrow gaps between the bars. Coals burn best with air coming in from underneath, so need a grate with reasonable gaps in the bars.

A multi fuel stove will have adjustable top and bottom air intakes and a compromise in grate  spacing to suit both fuel types.

What a clear and useful description! I can never quite remember which of the controls (top or bottom) to use on my house stoves but will do now. I also won't be so fussy about clearing the ash from the griddle/grate when I set the fire with logs. Thank you ☺️

Edited December 13, 2023 by MrsM

[DShK]

What's the physics behind wood liking to burn with air from the top? I've never really understood it. From the bottom should work like a rocket stove - air drawn in from the bottom, heated and rising up the flue. This movement causes pressure which sucks in more air, which burns better which increases the pressure. You control this by physically limiting the air intake. What's the process that happens that means wood burns better not this way but from air above?

[Ianws]

I think it would burn fine with air from below, but probably better/quicker than required. Not needed and wasting fuel.

Edited December 13, 2023 by Ianws

[Guest]

Our Charnwood C5 is multi fuel by virtue of the optional riddle grate. Without the optional riddle grate it is a wood burner only. We burn wood on a bed of smokeless.

 

It does however only have a single lever air control and it's at the bottom.

 

So if I was only to burn wood I am unsure as to if this would fare as a wood burner only.

[tree monkey]

6 hours ago, DShK said:

What's the physics behind wood liking to burn with air from the top? I've never really understood it. From the bottom should work like a rocket stove - air drawn in from the bottom, heated and rising up the flue. This movement causes pressure which sucks in more air, which burns better which increases the pressure. You control this by physically limiting the air intake. What's the process that happens that means wood burns better not this way but from air above?

I've wondered about this and I couldn't find anything specific but ...

 

Wood will burn with bottom air but it's difficult to control and you will use a lot of fuel, so I think its more of a control issue than anything else.

 

Coal on the other hand is actually difficult to burn, it needs bottom air, try burning coal in a BBQ or similar and it just goes out.

 

In effect wood is easy to burn but to have any sort of control its best to keep a bed of ash, coal is a bugger to burn and needs the bottom air to support its combustion 

[BWM]

As a generalisation multi fuel stoves are heavier built and many have some form of baffle between fire and flue.

[truckcab79]

33 minutes ago, BWM said:

As a generalisation multi fuel stoves are heavier built and many have some form of baffle between fire and flue.

I’ll just give it a go and see what burns and how well I think.  Appreciate all of the above replies but some applies to mine and some doesn’t so trial and error the only way forward I guess.  

[magnetman]

That fire will burn anything. 

 

Wood if you can get it during the day then a couple of shovels of smoke less briquettes and it'll stay in overnight. With the rope sealed door you might even be able to turn it orf. 

 

I had a similar fire once (Villager Heron) which was so well sealed one could have a roaring fire one minute then close everything up and it went out. Quite handy sometimes. 

 

 

Make up a L shaped tool from something like a 5mm steel rod so you can rake the gaps in the grate from underneath. 

 

 

Something like this. Wants to be reasonably thick rod for durability.

 

3 hours ago, truckcab79 said:

I’ll just give it a go and see what burns and how well I think.  

 

[DShK]

5 hours ago, tree monkey said:

I've wondered about this and I couldn't find anything specific but ...

 

Wood will burn with bottom air but it's difficult to control and you will use a lot of fuel, so I think its more of a control issue than anything else.

 

Coal on the other hand is actually difficult to burn, it needs bottom air, try burning coal in a BBQ or similar and it just goes out.

 

In effect wood is easy to burn but to have any sort of control its best to keep a bed of ash, coal is a bugger to burn and needs the bottom air to support its combustion 

That makes a lot of sense! Thank you for your insight.

[magnetman]

The other thing with wood is that a high proportion of the energy is in the smoke. If you put air in underneath you eject the smoke from the chimney but if you put air (preferably preheated) in above the fire itself the smoke can burn and release energy. 

 

There is an awful lot of energy in the smoke. Any smoke being ejected from the flue is lost energy. It won't burn properly until about 600'C. Proper secondary jets are quite impressive when they get going. 

 

Having said that this doesn't mean a fire with only a bottom air input won't burn wood. It will but you won't get the full combustion and will tend to block the flue more than a fire with the preheated secondary air tubes. 

A fire burning wood at the correct temperature with secondary air won't make any smoke even when a new piece of wood is put on because the smoke is consumed in the firebox. 

 

 

I have two virtually identical fires one with the preheated secondary air and the other without. Their performance when burning wood is completely different. One gets the flue (80mm) blocked often and the other one never gets the flue (70mm) blocked at all despite it being even smaller diameter. 

 

 

[DShK]

Interesting. Also thanks for the insight. What does the setup look like for preheated air?

[truckcab79]

On 14/12/2023 at 11:32, magnetman said:

The other thing with wood is that a high proportion of the energy is in the smoke. If you put air in underneath you eject the smoke from the chimney but if you put air (preferably preheated) in above the fire itself the smoke can burn and release energy. 

 

There is an awful lot of energy in the smoke. Any smoke being ejected from the flue is lost energy. It won't burn properly until about 600'C. Proper secondary jets are quite impressive when they get going. 

 

Having said that this doesn't mean a fire with only a bottom air input won't burn wood. It will but you won't get the full combustion and will tend to block the flue more than a fire with the preheated secondary air tubes. 

A fire burning wood at the correct temperature with secondary air won't make any smoke even when a new piece of wood is put on because the smoke is consumed in the firebox. 

 

 

I have two virtually identical fires one with the preheated secondary air and the other without. Their performance when burning wood is completely different. One gets the flue (80mm) blocked often and the other one never gets the flue (70mm) blocked at all despite it being even smaller diameter. 

 

 

Makes sense.  I build traditional wood-fired ovens for clients (pizza ovens to most people - but capable of far more than that). Once going they emit no smoke whatsoever. Never thought why until I read your post.  All you’ll see from the flue / chimney is heat haze. 

[magnetman]

2 hours ago, DShK said:

Interesting. Also thanks for the insight. What does the setup look like for preheated air?

 

Some fires pull air from the base at the back and route it into the firebox

 

On mine we just put lengths of angle iron welded on each side vertically with a one inch hole in the side of the fire each side and the ange irons capped by a little steel triangle. Little deflectors on the inside to route the air slightly downwards. These tubes start just above the base of the fire.

 

So the air is drawn in at a low level, heated up because the fire is hot and injected above the burning fuel.

 

If you inject cold air into a fire you are discouraging it but hot air, although it contains less oxygen, is very useful. Once hot enough there are little jets of flame from the inlets. Sometimes if very hot these are blue flames because it is the gas in the smoke which is burning.

 

 

 

 

[truckcab79]

Should just add that since restoring it I have lit it only once, to fire the mortar on the new fire bricks. Used some kiln dried ash. Burnt lovely but it’s only small so the size of wood you can put in means it burns relatively quickly.  Hence thinking coal or some sort of man made heat log might be a better option once it finally gets installed.  

[magnetman]

It will stay in for a long time on smoke less briquettes. A lot of people seem to like Excel. I find it too smelly. There are others. Homefire is usually pretty reliable. I expect Phil at the marina office has a stock of coal. 

 

Lignite Briquettes from Mole Valley farmers are quite good as well. 

 

 

[truckcab79]

1 hour ago, magnetman said:

It will stay in for a long time on smoke less briquettes. A lot of people seem to like Excel. I find it too smelly. There are others. Homefire is usually pretty reliable. I expect Phil at the marina office has a stock of coal. 

 

Lignite Briquettes from Mole Valley farmers are quite good as well. 

 

 

 

Cheers. Yep. Always a stock of coal in the chandlery but the stove is currently in my workshop 😂. Won’t be using it for a while.  I’ve always got mountains of kiln dried Ash at home for the wood fired oven so just used what I had at hand for a first burn.  Will try the briquettes.  Doesn’t seem as ‘romantic’ as burning wood but the novelty will wear off quickly if I’m chucking more on every two minutes. 

[IanD]

On 15/12/2023 at 12:30, truckcab79 said:

Makes sense.  I build traditional wood-fired ovens for clients (pizza ovens to most people - but capable of far more than that). Once going they emit no smoke whatsoever. Never thought why until I read your post.  All you’ll see from the flue / chimney is heat haze. 

You do know that PM2.5 particles -- the ones that do the most damage -- are invisible?

[magnetman]

17 minutes ago, truckcab79 said:

 

Cheers. Yep. Always a stock of coal in the chandlery but the stove is currently in my workshop 😂. Won’t be using it for a while.  I’ve always got mountains of kiln dried Ash at home for the wood fired oven so just used what I had at hand for a first burn.  Will try the briquettes.  Doesn’t seem as ‘romantic’ as burning wood but the novelty will wear off quickly if I’m chucking more on every two minutes. 

Yes my fire which is about the same size except tall and narrow needs topping up with wood every hour or so. It does keep the boat toasty even with the doors open. 

 

I like a wood fire and fortunately this one will run okay with the door open. Problem with Boat fires is usually the glass goes black and generally they don't like door being open and smoke into the cabin so you often don't get to see the flame anyway. Some people clean the glass regularly of course. 

 

 

 

 

10 minutes ago, IanD said:

You do know that PM2.5 particles -- the ones that do the most damage -- are invisible?

Its the coughing which carries you off not the coffin they carry you off in.