Heat loss over mass

Hello all. I am wondering if anyone knows the approximate temperature of a 5” system exit duct burning at its peak. By exit duct I mean the point closest to the barrel. I am also wondering how that temperate dissipates over the course of the duct. For example if I had a 20’ bench, what would the initial output be and what would the exhaust at the end be. Another question is how heat runs through cob. Will it maintain the temperature of the duct if given enough time? Or does it fall significantly?

Thank you in advance for anyone who knows and would like to share

Cheers,
Dean.

Hi Dean;
Average temps at your transition area entering the mass will be in the 200-400F range maybe 500F max.
The desired exit temperature leaving your mass is 150-200F.
Cob absorbs heat slowly and then releases it the same way.
Your mass ideally is composed mainly of large heavy rock.
The cob is nearly a filler to remove any air pockets or/and as a finished exterior.


At 20' you are nearing the limit for a 5" J-Tube remember each 90-degree turn is a 5' deduction.
I believe a 5" is safe to push 25' horizontally.

Thank you much Thomas! Do you have any idea what the heat loss is over say, 4 inches of cob? Or 2? My reason for asking is I plan to run pex pipe through my cob bench as a method to slowly heat water without boiling it. How hot would cob be 4” out from the 2-500 degree duct? It’s tricky, I’ve got to be under boiling but above cold so it doesn’t take for ever and ever to heat up my water.

Dean Chiasson wrote:Thank you much Thomas! Do you have any idea what the heat loss is over say, 4 inches of cob? Or 2? My reason for asking is I plan to run pex pipe through my cob bench as a method to slowly heat water without boiling it. How hot would cob be 4” out from the 2-500 degree duct? It’s tricky, I’ve got to be under boiling but above cold so it doesn’t take for ever and ever to heat up my water.

Heat transfers through the cob very slowly 1in an hour. If you are running water through that pipe you will pull off heat faster than it can transfer through the cob.