(Intake-heat exchanger --- Outlet) / (Intake-heat exchanger --- Intake boiler inlet).
We can apply corrective factors with specific heat and condensation, but the essential is in this basic formula.
All the exchangers are undersized, the gases come out too hot in the evacuation (except condensation) at full flow and therefore it is in the interest of reducing the combustion flow and therefore of the gases in the exchanger to greatly increase the efficiency while leaving the time for the gases to cool down against the exchanger before leaving. It is simple to measure the temperature in the gases at the outlet and reduce it as much as possible. The efficiency can thus be doubled and even more at low speed by heating slowly .
This avoids complex measurements and calculations and can be adjusted efficiently.
Reducing the power of operation greatly reduces its heating bill especially in mild weather where there is little heating. In very cold weather with cold water returning from the radiators the gases are more cooled and the flow can be increased by keeping the same temperature of the evacuated gases.
My heating bill is thus improved.
With a chimney and the inserts the yield becomes ridiculous with outbreaks too strong because all the heat goes into the chimney! We can burn wood for nothing.
Ordinary boilers do not regulate their performance by controlling the temperature of the exhaust gas.
