Mixing Logs & Coal?

[Witterings]

I've got a multifuel stove but believed you should either burn logs OR coal but not mix them. From memory I think part of the reason was your meant to use the vent underneath if it's logs and the vent in the door if it's coal.

 

Anybody know if you should / shouldn't and the reasoning behind it?  

[Peasgood]

I think the reason is the mix can cause acids that eat into the metal quite aggressively.

 

[GarethM]

Primarily coal also contains sulphur, so sulphuric acid and such.

[openspaceman]

30 minutes ago, GarethM said:

Primarily coal also contains sulphur, so sulphuric acid and such.

It would be sulphurous acid.

 

My main reason would be I would not risk coal ash on the garden whereas I do put wood ash on it.

[GarethM]

14 minutes ago, openspaceman said:

It would be sulphurous acid.

 

My main reason would be I would not risk coal ash on the garden whereas I do put wood ash on it.

It's good for keeping slugs off things tho.

[peds]

You should start a gardening tips podcast.

[Steven P]

Coal needs air through the grate, wood works best with top air. However it will all burn on a fire set for coal. If you have a coal fire with no airflow from underneath you can burn through the grate. I reckon coal is also bad for the fire bricks.

 

Coal gives of sulpher (dioxide, acid, whatever) which if it gets damp can turn into sulphuric acid / sulphurous acid (sorry, GCSE chemistry was a while ago, sulpher + moisture -> acid) which could condense onto the chimney or flu walls if the flu walls are still cold or cooling at the end of the day. When everything is warmed up you'll get minimal sulphuric acid condensing.

 

Coal ashes can contain nasty stuff so shouldn't be spread on a garden like wood ash.

 

If it was me, I'd start with a good hot wood fire to get everything warm - mid winter though, my chimney rarely cools enough to be a problem, and then switch to coal burning. I might have a mix of both if I wanted better flames (showing off for having company in the house perhaps), rarely burn them both at the same time but might swap from 1 to the other part way through a day (for example, a coal fire if I am going to the shops, lasts longer, and then a wood fire in the evening).

 

If burning both, I'll set the bottom air as if it is a coal fire and adjust the top so that the wood burns well.

 

Ashes, I have a separate pile for coal ash which sits for a couple of years and the nasties leach out - then I think it is OK to use kind of like a sharp sand. It is also pretty good to go on the road when it is iced over (cold of course), gives extra grip, black colour absorbs sun energy and warms up quicker, sawdust also goes on the road if I want to be more green about things/

[openspaceman]

43 minutes ago, Steven P said:

Coal gives of sulpher (dioxide, acid, whatever) which if it gets damp can turn into sulphuric acid / sulphurous acid (sorry, GCSE chemistry was a while ago, sulpher + moisture -> acid) which could condense onto the chimney or flu walls if the flu walls are still cold or cooling at the end of the day. When everything is warmed up you'll get minimal sulphuric acid condensing.

Just to remind you of your CSE; sulphur in coal burns to sulphur dioxide,SO2, if there is liquid water in the flue this combines to form  sulphurous acid, H2SO3. This can, and does, eat through a stainless steel liner by reacting with the protecting chromium oxide layer and then attacking the iron content. Bone dry wood produces water as a product of combustion whereas coal produces little and of course wood at 20% mc produces much more.

 

As you say as long as the dew point of water in the exhaust gases is not reached it will not condense and the sulphur dioxide will stay as a gas and be exhausted.

[Witterings]

Cheers for everyone's replies, think it's made my mind up as I have quite a lot of wood and would have to pay for coal I'll probably stick with wood although I did fancy not having to top it up quite so frequently hence why the coal appealed.

That said, if coal ash is a slug killer I could be awfully tempted to have a change of heart as we're plagued with the bloomin critters 😄

[peds]

Recommend trying to control slugs using methods that won't render your soil incapable of supporting life.

Encourage frogs, hedgehogs, songbirds into your garden. 

Consider ducks.