Hey Pete;
I see we have another mad rocket scientist in the making here!
Keep wearing your regular clothing until your Lab coat and dorky glasses arrive... mail service is slow with the current medical problems!
So why would someone still make a J tube and piped mass?
To start, a J tube is so easy to build and a batch box requires some metal fabrication. Many choose to start with the J and later they will upgrade to a Batch.
Now in my opinion, a piped mass is outdated, and bells are a much better idea!
But many folks worry that a bell surely would leak
carbon monoxide into their home. Other than maybe a little smoke at start up nothing leaks indoors.
Installing a "bypass" gate eliminates any cold chimney (draft) problems.
Is an empty bell as warm as a solid piped mass? There is some debate about which is longer lasting.
I think that the solid mass once it is completely warm would hold heat a little longer... but not
enough for me to build one anymore.
We lived with an 8" J tube and solid mass for 7 years, They work outstanding but you must pop in to add wood every 45 minutes or so.
Our is in an uninsulated
greenhouse in Northern Montana, we keep it heated all winter with no fire at all from 9pm - 7am. -10 F outdoors and 40F indoors in the morning!
Feeding it all day was no big deal, just another chore.
Last year I removed the 8" J tube and replaced it with a 6" batchbox. I still utilize the 8" pipes and solid core, but now we have a much nicer, hotter burning stove that will last 2+ hrs before needing wood added.
My shop had an 8" J tube going into a large brick bell. I converted it into a 7" batchbox! I love it, Much warmer with a batch and less adding wood.
Next ceramic board (CFB) versus fire brick)
In my opinion the CFB works super as long as it is nowhere near the wood.
The CFB is to easy to damage, any wood that bounces off a wall or roof WILL dent/ damage the CFB. Let that happen a dozen times and suddenly you need to replace your CFB.
When a batchbox is up flying (we call them Dragons) it is very similar to a forge... white hot, when you open the door to add wood either you wear a welding glove OR you quickly toss in wood and shut the door... that is when you will damage your CFB.
When you build with firebrick you have no issues with damage unless you are brutal.
But you must allow those bricks to get up to temperature before you can expect your
Dragon to soar.
Rules about bell size.
Yes there are definite size limitations listed on Peter Bergs site. ISA internal surface area of the bell.
However by installing a bypass to heat the chimney and start the draft you can exceed those ISA numbers.
With several bypasses installed a person could have an enormous series of bells. Most of us stick close to Peters numbers but we still install a bypass to eliminate any startup draw issues.
Matt's tiny cookstove with the glass top really throws quick heat just like a barrel and it can be plumbed directly into a bell or bench to mass heat or it can be run as just a stove for those days when you just want to take the chill off not bake yourself out of doors!
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