This study, see link at bottom, from Denmark explains stratification and some of the concepts being used inside the tank. It is for solar storage but the concepts apply to wood boilers
I'm sure some of these ideas could be homebuilt.
If you have a system that can take advantage of those stratification layers and principles I think a vertical tank would work best.
If your system requires 180 supply and you run the tank at 180- 190, really the stratification levels don't do much for you.
In a typical Euro system they may use the upper, highest temperature, layer for DHW generation. It's rare to see any heating device, over there require over 140F supply. It may be code in some areas in fact. Early Euro imported boilers were set to a max. 75C (167F) on their controls. Some still are. So the next stratification level down would supply panel rads, which are more common than radiant floor in much of Europe.
Then the lowest level of temperature could supply a radiant floor with 100-120F supply.
Then of course the coolest part of the tank, the very bottom returns to the heat input device. Condensing boilers excel at low return temperatures, as do solar arrays, so that bottom cold temperature really drives the efficiency of the heat supplier up.
I think it would be hard to layer a 20" diameter horizontal tank as effectively.
I know long term heat loss from a large tank is hard to model. I've asked some engineers and tank manufactures to do that
![Smile :) :)](/talk/styles/default/xenforo/smileys/grin.gif)
As the temperature is ever changing inside the tank at those stratification levels. Tanks can easily vary 30F or more from top to bottom. The heat loss changes as the temperature levels change and the ambient air and infiltration changes. Even in a lab setting with sensors every 2" on the tank it's hard to pin down exact numbers. So they tell me.
www.preheat.org/fileadmin/preheat/d...bo_Heat_storage_for_solar_heating_systems.pdf
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