Wood burning stove 'wash' and stuff...

Bendy_House

Hi.

About to collect a gas-burning stove - a 'Yeoman Exe' - bought cheaply (that's me) on t'Bay, with a view to converting it to 'solid'. No idea yet how the current model is air-supplied - eg from underneath, or front or whatevs - but it has a conventional flue like most of the models in the range, regardless of fuel type. And the general physical construction is the same - ie cast iron, with a large opening front door with glass (but with a 'hidden' lock on the gas model).

I'll need to add a method of controlling the incoming air supply for the log-burning conversion. I've read folk talk about air 'wash', which seems to be an air supply from 'above', and others even saying that wood fires should ONLY be fed from above, which strikes me as being weird - I currently burn timber in an open fire, so that gets its supply from below, I presume. Tho' air gets to it from everywhere...

Soooo, anyone know the science around air flow to a log burner?! Will a 'bottom' air supply be enough, or will it also need air to the burning flames?

Ta

QrizB

In very broad terms, I understand wood is usually fed air from above but solid fuel needs a raised grate and airflow from below.

You can burn wood on a grate too (I did for years) but don't try burning solid fuel without one.

I'm not at all familiar with gas-fired cast iron stoves so don't know quite what you'll find with the Exe.

It sounds an interesting project. Good luck and keep this thread updated with progress - and photos if you can!

Bendy_House

Thanks, Q, and will do.

Burning wood in my normal open fire is also on the standard raised grate, so it clearly works. But I do appreciate that a, perhaps, secondary air flow from above helps the timber to burn more efficiently, presumably as the gases being released need this to burn fully. Probably better environmentally too. 

As you say, it'll be interesting! 

Apodemus

Yes, interesting project.  I would have thought it might be possible to track down some airflow diagrams for the models that you are working with, to see what the differences are? 

Most woodstoves have a primary air feed from low on the front door (or on the ash panel, if it is separate) and a secondary air source from higher up, for the air-wash.  The air wash is partly cosmetic - you want to be able to see through the glass, without having to wash it every few days - and partly to improve secondary combustion,  But I believe that the newish DEFRA regs mean that all stoves have to have a secondary air flow that can't be completely closed off.  The change to the DEFRA approval was to stop people closing the stoves right down overnight, leaving them slowly smouldering and releasing particulates into the neighbourhood.  The downside is that it it is much more difficult to get a modern woodburner to stay lit overnight.

When I was trying to repair an old wood burner (early 70's model), I found that our local stove shop was really helpful.  Their parts store was full of all manner of parts that you wouldn't even know to look for and the guys there were happy to wander around with me (and a measuring tape) trying to work out which parts from other stoves might be pressed into service.

The funny thing is that I had been wondering about putting a gas burner in the old woodburner for use as a workshop heater!  

Bendy_House

Cheers.

I suspect there will be a sizeable opening on the underside for the gas burner, so first task will be to seal that off and add some form of draught control to it. I'll see how that goes, and then consider some additional vents higher up if it looks as tho' it'll be of benefit, but I suspect these would need to be on the sides as front space is very limited.

Anyhoo, we'll see

Apodemus

Bendy, you should be able to see an exploded diagram at Yeomanspares.com and track down your particular model, then compare with the nearest wood-burning version.  From what I can see, there is a substantial difference to the internals and the carcase between gas and wood.  Gas seems to have ceramic plates instead of firebricks.  But more importantly it looks as if it has an internal metal box which includes a floor and the outer casing lacks the main floor that the wood burning equivalent has.  So, once you have removed the internals, it looks as if you might have to fabricate and install a bottom plate for it.  

Bendy_House

Thanks Apod - I did check out their site, but obviously missed a lot of stuff!

Yes, I anticipate a bit of work. I am expecting to have to fit fire bricks, block off the underside in a 'regulateable' manner, and fit a cast basket at the very least. Possibly even a metal deflecting plate above the flame to direct it around before exiting the flue. 

I'm not too concerned about getting it spot on, as wood has burned successfully in our open fire, with just the standard cast iron grate. My main issues with the open fire are the loss of heat up t'flue when the fire isn't being used (most of the time), and I can't be bothered to plug the flue to prevent this. And also spitting from the fire, which often necessitates the use of a screen - a hateful device. I expect this to be a significant improvement.

The actual overall construction is the same, I believe - solid cast iron body, door and flue.

Apodemus

Bendy_House said:

The actual overall construction is the same, I believe - solid cast iron body, door and flue.

Are you sure it's cast?  I thought I saw welded steel on one of the bits of that Yeoman site, but that might have been a different stove.  With a bit of luck it will be the same casting as the wood version and you can fit the standard top baffle plate.  In most stoves, the baffle plates take most of the heat and eventually warp, needing replaced, so they are normally quite easy to source.  This is where a trip to your local stove spares shop will be useful, as you will be able to measure the plate you need and find one that is a reasonable fit - potentially from some other unrelated stove.  The same with firebricks, standard pieces that you cut to shape will probably work out cheaper than the pre-shaped ones for the actual stove.

As an aside, I never use the primary air-flow reguation on my woodburner.  Door slightly open until it is burning well, then regulate it with the secondary air-flow lever (this is actually the recommended way with my stove and you see the same advice for other stoves).  So you could probably get away with only a single air vent higher up, which might make construction a bit easier.  (Although a top vent will need to cope with heat, while a bottom one could be in a cold part of the stove).

Apodemus

Oh, another thought!  On my old wood stove, the top baffle plate was simply hung on a couple of threaded rods with the back resting against a ledge on the stove - the rods were bent at the top to hang from lugs on the underside of the stove top and then passed through a simple hole in the plate and the weight of the plate hanging against a nut on the bottom of the threaded rod.  This loose arrangement allowed for differential expansion of all the parts without it falling off or cracking.  That sort of system might be quite easy to replicate if you find that your casing doesn't have the slide castings for the "correct" baffle plate. 

Bendy_House

Cheers, Apod.

Yup, not sure if the body is cast - I was going by the pic, and the door looked to be, but I don't have the stove yet - picking it up next weekend.

Cheers, good info. I recall such a plate in another stove we had many moons ago - it just sat on two points (bolts coming through from the rear) at the back, and leant on the front at a slope, above the door.

Effician

Don't know if you have the manual for the yeoman exe wood stove but found one here just in case,

 https://www.woodburnerwarehouse.co.uk/media/wysiwyg/pdf/Yeoman/Exmoor_Exe_Devon_CountyMk2 Installation & User Instructions.pdf

For the gas one,  https://manualsdump.com/en/manuals/yeoman-pr1145/44844/20

About 33kg weight difference between wood & gas stove so will be interesting to see exactly how much you need to add.