Net stack temperature subtracts combustion air temperature from the reading. Logged at the same firing rate over time, a rising stack temperature means heat is not getting through: soot on the fireside or scale on the waterside. A common rule is about 1 percent efficiency lost for every 40 degrees F rise. Too low a stack temperature in a non-condensing boiler means condensation and corrosion.
Stack temperature's up 80 degrees since the last tune-up, the tubes are dirty, schedule a brushing.
Also heard as
- stack temp
- flue gas temperature
Related terms
Flue gas
The hot exhaust that leaves the boiler after combustion, made up mostly of nitrogen, carbon dioxide, water vapor and leftover oxygen.
Combustion analysis
Testing a burner's flue gas for oxygen, CO, CO2 and temperature to set it up safely and efficiently.
Scale
A hard mineral crust that forms on boiler heat transfer surfaces from calcium, magnesium and silica in the water.
Punch the tubes
To clean soot from firetube boiler tubes by running a brush on a long rod through each one.