Floor channel conversion

Hey just wanted to share my conversion of my batch rocket 8”. I originally built this stove 5 years ago and it has ran very well with a p-channel in place.

However this year I decided to replace the barrel oven door with a nice glass door and at the same time take out the p-channel and replace with a floor channel.


Finished up the door and cob last night and did a test burn this morning. This is when I realized that I forgot to adjust the port height after the floor got raised!  

Ran the right direction but wasn’t the cleanest of burns to say the least. I’ll make sure to report back once it modify the port to the correct size. Anyone else have info from their conversions?

Looking good Daniel!
Thanks for sharing.
Easy to forget port height and hard not to notice with the first fire!
Keep us posted as you improve.

Hi Daniel,
Sorry I don't have any specific information but can give you the link to my conversion.
I know somewhere I was playing around with the port height (from Peter's recommended 9.5" high reduced to 9" so I didn't have to make the cut in the firebrick).  I don't recall experiencing much difference, of course I didn't have a gas analyzer also.

https://permies.com/t/132799/tube-Batch-Box-Conversion

Good luck with your experiments and do keep us posted of your findings

Yes I don’t think the half inch will greatly change it. Mine went from 13 to 11. The 15% reduction  seems to have made much more of a difference. I’m going to let it cool down a bit more and the cut the port two inches taller.

Port fixed and now this thing is roaring again. Took off so much better and no smoke back. Thanks everyone. Will post photos once the plaster is on.

That glass door adds a whole new dimension to lighting a fire doesn't it Daniel?
Good job on the upgrade

For sure. Love the glass.  For those interested this one is from firespeaking.com. Expensive but really great quality.

Daniel Ray wrote:Port fixed and now this thing is roaring again. Took off so much better and no smoke back. Thanks everyone. Will post photos once the plaster is on.

Thanks for the update report. It feels so good that the proportions I came up with about 11 years ago are still valid today. You were able to tell the difference, fixed it and the thingy worked again as it should. Lots of people doing their first build didn't know how it should work and kept the thing, fighting it every winter.
Question: how 's the p-channel's detoriation in 5 years? Just curious.

Peter, not actually much at all. I tossed it or else I would post a photo, but I would say it deteriorated about 6mm at the most.  It wasn't much, though with my house I was only burning about 2 cords a year.

A huge thanks to your ever handy proportions table which I've used probably a thousand plus times in these last five years.

Those interested, the floor channel is a product of https://dragontechrmh.com/ and uses the RA330 stub which shouldn't deteriorate anytime soon. I'm also going to be building a 6" batch in a friend's house soon and will document and post accordingly.

Because I'm here typing and didn't see it any other place, what is the recommended floor space in the batch between the main air inlet and the floor channel where the cool air pools? Have the greater RMH minds figured out a percentage for that to use between different size stoves?

Daniel Ray wrote:Because I'm here typing and didn't see it any other place, what is the recommended floor space in the batch between the main air inlet and the floor channel where the cool air pools? Have the greater RMH minds figured out a percentage for that to use between different size stoves?

In my heater, which has been used as a test bed for the floor channel, this distance between the main air inlet and the floor channel's mouth is about 50 mm or 2". Translated to your 8" model, that could be 30% linear distance more, totalling 65 mm or 2.6". Your setup as it is now has the disadvantage of ashes that are tend to fall out of the heater as soon as the door is opened.

May I recommend a threshold, the piece of flat or angular steel on top of the floor channel's feed? Right at the beginning of the feed, ash will be kept inside and fuel won't roll out easily. Starting up will be a bit slower, depending on the height of the threshold. While the core is heating up, the shift to more secondary air is more pronounced due to the increased volume of the cold air pool. Height of the threshold isn't fixed as such, mine is about 60 mm high. The ash bed can be allowed to grow in volume, next fire on top of the ash bed. Until it's too much, some but not all can be scooped out. There's a tendency to leave more charcoal at the end of the burn. Leave this in and start the next fire on top, this will ignite the lower down logs much easier.

Thanks Peter, I think Ill add that in as I was already identifying that as an issue. I wasn't initially sure about the spacing, but I do have it at 2.5 inches so that is pretty darn close.

Plaster done. May follow up with a milk paint for color and protection.

A++ Daniel
Thank you for the updates

Nice job on that rebuild! So, instead of using the RA330 material for the stub, why not just use a 6" piece of sacrificial exhaust pipe (for a few pennies) and plan on annual replacement (or more frequently if needed) as we do our normal inspection and maintenance. That RA330 stub has no cobra head. Has it been determined that that deflector is not actually necessary? --and is 6" enough length to get the secondary air where it needs to be? By the way, I'm working on an 8" build.

I'm assembling materials for an 8" BBR heater with a floor channel. I've got  2x4" rectangular steel channel and 2" SS 304 SS exhaust tubing for the stub. I've also gotten a 316 SS handrail base flange allowing easy stub replacement when needed. How tall does the stub need to be for an 8" system? I see someone selling 6 inch pieces of RA330 material for the stub. Is that tall enough? -- or should it be "Peter's recommended 9.5" high" that I'm seeing here in a previous post? I'm not seeing dimensions for the stub height. Maybe I've just overlooked it?? And does it need that cobra hood or can it just vent straight up in front of the port?

Also, what is being used for the roof of the firebox? I've got 12x24" ceramic floor tiles that would work if they'll hold up to the repeated heat/cool cycles. Seems like they should be OK?

Edit: Now I'm reading on Peter's site, "air is supplied halfway up the port which in turn keeps the double vortex low in the riser on average." I guess that would make the stub about 6" tall.

Hi Leslie;
Indeed the air stubs are optimal at 6".
The open top seems to work as well as the cobra design.

Batchbox tops can get hot fast.
I use a cast iron top on my 7" and a 2" thick 12x24" heavy firebrick on my 6".
The cast iron has changed color and warped at the hottest portion of the box.
The heavy firebrick is as good as new.
Some folks use Kiln shelves as a roof and they seem to work well.
Your ceramic tile hopefully will perform as well.

How long you burn your batch will affect roof longevity.
My batches both get extreme burning,  a normal batch (inside an insulated home) is only burned once or twice a day.

As your tile is an unknown roof material, I suggest having a backup plan if it suddenly chooses to crack/break this winter.

Batchbox roofs do not have to be flat, they can be built with conventional size firebricks if needed.

I dont think a ceramic floor tile will last 5 minutes!

I did an experiment with a 24" square x 1" thick ceramic  ( tile- solid piece- flat plate, what ever you want to call it) perhaps even call it porcelain. something I would never think of being able to drill through, but considered tuff as heck used as a tile.  

I thought it would be perfect as a top for batch box.. and I did a pre-test with fairly spread out heat, but intense. In the 1000 F range..

it was on my test box, and I was out of the room when it exploded.  I can only guess, that the center was trying to expand before the edges had a change to expand at the same right. it was spectacular, with perhaps 3-400 pieces all over the room. Was feeling good I was not in the room, but even better that I tested it first. before building into the stove.  

Of course there are many products and types of these tiles, some might work, but how they expand might be the problem to deal with..  Not saying they are right wrong for the task, but as a outside shell with the capability to  expand and contract might be a better use.