Dear Supermax,
Do you need the answer only for this type of design or substitute will do.
We have a indirect type natural gas heater which maintains the outlet gas temp to the required setpoint.(55 DegC)
in this water is heated by using the same gas in the burners and water is heated up to @70...
Dear Jabonet,
To answer fully to your question it is necesary to know the thermal conductivity of the material using for the construction of the furnace. if it is known then the following formulla can be used to calculate the heat transfer through the wall.
(T2-T1)
Q = K*A* -------...