Pete Johnson

Hi Kevin.. yes, it should be pulling more heat down the bench. We were going to try and carry the pipe on round the bench corner, but more turns and longer flue pipe would reduce the draw too much.
We used a design from Matt Walker (who was brilliantly helpful all the way through!).. Best.. Pete

Thanks so much for the replies and kind comments!
The slit along the bottom + blocking the end for more stratification sounds like a great idea.. I'll def have a go at that when I open it up.
I've got alot more to learn about testing the moisture levels too - Matt said moisture levels using a meter are taken by splitting the log and testing the inside. I was getting 20% on the outside which means the wood is wetter than that in real terms.  
I've split a couple of loads up (mostly ash) and will leave it stacked under a roof for next year.
Using the heatlogs is quite different. They're really dry, so burn well and no smoky start-ups now, but they're designed to have a really high BTU, so I can only really put a few in at a time.. don't think I could fill the batch as I was with wood - it feels like that would be too much heat - we can get the batch about 1/3 full max.  We do then also end up dropping one or two 5" heatlogs on to the embers of the last and keeeping it ticking. This feels a bit more like conventional woodstove use, and although the body and bench do get really hot and stay hot, I know that's not how these systems are designed to run. Although the heatlogs are also designed to smoke as little as possible, I'll need to open it up and see how dirty it is inside.
As soon as I do that I'll report back...
Thanks again for everyone's feedback!

Hi Satamax
Sorry for the delay in getting back on here.. busy times!
I've messaged Matt about it and his take was to definitely leave wood to dry for multiple years (minimum 3) and possibly removing some insulation from the chimney flue where it runs near to the heat riser to help with smoky start-ups. He also gave me ALOT of info on different ways of measuring and issues around putting a number on wood moisture. Of course there's lots more to it than I understand!

I do want to try and keep the system retaining as much heat as possible, so I haven't removed chimney insulation.. instead I bought a 1/2 pallet of compressed sawdust heatlogs as locally as possible and paper wrapped. They work really well. Our smoke problems are pretty much gone (now just puffs a tiny bit from the kindling when it's starting up from really cold).  

I didn't extend the chimney flue round into that 2nd section of bench, and the back wall of that bench is a solid internal wall of the house (bathroom on the other side). It works really nicely as a very low level radiator in the bathroom to take the edge off the cold, but I realise I might be at the limit of what I can expect from this configuration.

I did wonder - I should be trying to burn as quick and hot as possible right?  As I understand it, hottest fire combined with coolest chimney = most efficient use of fuel.
With the door on now, and using the heat logs, it is possible for the fuel to burn slower and cooler.. I guessing that might cause build up of nastiness in the system? Anything I really need to watch out for here?
I'm hoping to open it up in the coming weeks to see what's happening inside...

Thanks!!
Pete

Hi.. should add that we insulated the chimney flue..
Thanks!
Pete

Hey Satamax
Thanks for that.
I don’t know the ISA or exact internal measurements (I’m away working atm so can’t measure - can do when I’m back).
Design is a Matt Walker 6” batch heater with a 6” chimney flue.
We started with a single leg of bench heated.. it worked great, so we added the second. I think it still worked well, but quite shortly afterwards we ran out of 2 year seasoned wood and started running into problems.
We could try and go back to one leg heated and see what difference that makes.
I’ve attached some pics of the build in case anything jumps out at you..
Thanks again!
Pete

Hi.. thanks for that.
I'm thinking restrictions are any narrow sections or bends in the system and any irregular shapes inside. Not sure I'll be able to change the shape of it much, but we could block off the second leg of bench at the point the bench turns the corner. That would reduce the overall bench leg by about 1/2 and also take out a 90 degree bend. Would that make a considerable difference do you think?
I'll open it up and make sure there aren't any temporary restrictions (bit of insulation fallen off, a pile of ash, etc) inside too..
Thanks again for your help!

Thanks for the kind words!

Phil - the flue runs vertically down to floor level through the bell then 90 degrees to horizontal and then turns 90 degrees and into the first section of bench. It stops about 1' from the wall at the far end of the first bench at the moment. We may extend it round the next corner depending on how it performs over the winter.

SA - oops..  didn't mean to imply that. We fired it up for the first time about a month ago. I had some wood that was a couple of years old (that burnt really well!). I'm planning to open the bench up to reinforce the concrete slab tops with more angle iron (mainly for piece of mind) soon, so will have a look and a good clean out then.

Thanks as ever for all your input!

Hi all
Thanks for the replies!
I’ve built a Matt Walker batch heater with a bench. Our bench is maybe on the ambitious side.. it’s 10’ long and L-shaped (round a 90 degree corner). Photos attached.
The whole experience was brilliant - Matt’s support throughout has been invaluable.  I did email him earlier and his take was similar to yours John - that wood like ash should really be seasoned for 3 years before it’s optimum for burning. Given that our heater was working really well on the 2 year seasoned it seems it will just be a case of storing enough wood to use in the years ahead.
Phil - I’ll look into measuring exhaust temp. Our chimney is about 13’ of twin-wall insulated flue in total, with about 5’ of that above the roof. There’s a 1.5’ section of single wall flue just after it exits the bell - I’m typically measuring 135 degrees F on the surface of the single wall flue, around 1’ above the bell top.
Thanks again!

Hi all
I suppose I'm just wondering if other people experience the same thing I am...

To work really well my RMH seems to need the wood to have a moisture content 10% or lower. It seems I can't buy local air-dried wood much less than 20% (although there are laws about how dry firewood should be), and buying kiln-dried wood defeats the point of why I built my heater.
My local firewood is mostly ash, due to dieback.

At <10% my stove is rockety and blazing.. vapourising wood very quickly into loads of brilliant heat.. but anything getting towards 15% and I get smoke, mass not heating up enough and a pretty weak fire.
When I first fired it up I was burning last winters firewood (so down maybe 2.5 years and undercover for probably 18 months) - it ripped!
Now I'm onto new stuff that is closer to 20%. I'm having to split it right down and dry it on the bench and bell top to try and keep the drying cycle going.
Obvs now I know this I'm stocking up and will be able to work a year ahead from next winter.

Just wondering if other people find the same? Realise that the drier the better probably, but maybe my RMH is a bit fussy somehow?

Thanks all!
Pete

Thanks for the replies! I've been loving working with the clay (non-caustic, re-useable, etc) so I think I'll give the clay / sand / toilet paper mix a go..