Benjamin Dinkel

That’s looking great, very clean fitting cuts for the manifold! I’m impressed.
12cm over the riser is fine.
And 8cm should also work. 4cm insulation and 4cm cob, no prob.
What are those curious chimneys in the background?

Thanks Glenn. Yes, I was counting with another barrel for scrap cuts.

Does anyone have some insight on the (lack of) the bypass? Is a "top of bench" bypass better than nothing?
If I imagine the flow of the gases, I would say theoretically yes.

Here's a first sketch:


The core and a small part of the bench are going to be in the kitchen.
Then the bench goes through the wall and a bigger bench is going to be located in the living room.
At the end of the bench it connects to the existing chimney (the little square on the right). Maybe the chimney will get a metal insert, maybe I'll use it as is. There's no option for a new chimney at another point. The roof was just renewed and we don't want to penetrate it anywhere else.

The biggest challenge I see at the moment is not having any bypass option. I'll be installing an opening where we connect to the old chimney to have an option to prime the chimney.
I could also install an extra exhaust pipe on the top of the bench, allowing the warmest air to exit in the beginning. That could act as kind of a bypass. Although the exhaust would still have to travel all the way to the end of the bench. Just not sink to the bottom.
Any opinions?

Hey Mark,
I'm going to be building a J-tube with a half barrel bench soon. So I was wondering whether you finished it and whether you have some advice, some lessons learned, something you would do differently this time?

How thick did you cover the top spot of the barrel in the end? Is the tenperature comfortable?

Thanks in advance

Unfortunately this build got postponed indefinitely. But I'm planning another, bigger J-tube for this autumn.

Could be fine, I’m not sure. I haven’t used it on the riser.
On the burn tunnel and feed tube it’s fine. And will also be cobbed over I assume.

Thank you Thomas for that update in RMHistory.

5 barrels would be more than enough

Great job Fred! And thanks for sharing.

Excuse me if this has already been discussed, but your barrel looks like galvanized steel to me... I don't know whether that will handle the heat without gassing off pretty toxic stuff. Or is it stainless steel?

I'll probably be building an 8" J-tube with half barrels soon.

My question now is, how many barrels can I use without running the risk of too much condensation and poor draft?
I have gathered that an 8" J is roughly like a 6" BBR, so that would mean a bell surface (CSA) of 5,3m^2.

With an entire barrel exposed on top of the riser (~2m2) that only leaves 3 more half barrels (0.85m2 each, plus two half lids).

In my first design idea I would need 4 half barrels. So maybe I have to partly cover the barrel over the riser?

Any input is welcome.

Hey Fred, how is the bench coming along?