Oversizing ISA on DSR2 with a bypass?

Hi folks,

I'm working on a design for a DSR2 based masonry heater/boiler, which I will post more about when I get a bit further.

For now, I want to understand more about ISA calculations for bell sizing, and what exactly happens when you oversize it.

I understand I will need a startup bypass, and I intend to have one. With that in mind, how far past the "limit" can you go?

For example, I'm looking at a 9" core, which should have an ISA of 123 sq ft. If I don't mind using a bypass for cold starts, can I double that?  Or even more?

Has anyone been experimenting in this direction?

I'm certain you will get better answers, probably from everyone :) but I thought the reason was that sizing the bell up too much won't allow it to get hot enough that the stove draws well.

I think if you have a bypass, it may not matter much how big your bell is.

Hi Chris;
Matt Walker suggested that you could have several bells, which you would open one at a time until they rise to temperature, and then open the next bell and the next.
This of course has you burning your batchbox non-stop. I call this extreme burning batchboxes, I am currently running two like that.
My third Batchbox however  I am burning as they were intended to be burned.
I only need two fires a day to keep our old house warm from end to end. I call it heating with bricks, not wood.

If you oversize the bell on a 9" you will need to keep the bypass cracked open, for quite a while.
Meanwhile, you will be sending hotter air out of your chimney and not getting the "heat" efficiency you would with a spec—sized bell.

There is no "rule" on how much oversize is allowed, as Peter does not recommend using bypasses with the first-generation batchboxes.

Once warm a batch will draft with no bypass, no problem.