[Bldg-sim] Steam Boiler Efficiency Ranges

Davidson, Tom TDavidson at DLBASSOCIATES.com
Tue Jul 21 07:35:41 PDT 2015

Dear Bldg-Sim list,

We are trying to determine the efficiency of an old gas-fired steam boiler that we plan to replace with a high-efficiency hot water boiler. We asked a company that tunes burners to take two combustion efficiency measurements - one before tuning and one after. Unfortunately the burner was operating so poorly prior to tuning that it messed up the combustion efficiency analyzer; it gave no readings and our opportunity to obtain a pre-implementation combustion efficiency value was lost. We do know that the burner was being starved of combustion air, but we aren't sure by how much, or how low the efficiency of a gas-fired boiler can drop before its safeties shut it off.

If anyone has successfully measured the efficiency of an operating boiler that is starved of combustion air, and is willing to share this efficiency, I would be quite grateful. I am looking your 'worst of the worst' efficiency measurements. The rest of our energy model Is nicely aligned with facility usage, but we would need to drop the overall efficiency of this boiler to less than 50% to align with utility data, and even this value assumes that we are generous in terms of modeling warm winter temperature setpoints, high infiltration rates, etc.

For reference the steam boiler we looked at is about 45 years old, made by the Federal Boiler Co. (Model AST 6 350).


Thomas A. Davidson, PE

DLB Associates  |  265 Industrial Way West  |  Eatontown, NJ 07724
tdavidson at dlbassociates.com  |  732-927-5108  |  f: 732-774-5000
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