Underfiring Smith GB200 Boiler

djthx

I checked my gas meter and was able to calculate that my GB200 4L was firing at 101,700 BTU/HR.  It's input is rated at 110K BTU/HR with a gross output of 88K BTU/HR (66K BTU/HR NET).  My Radiator Heating Capacity EDR is 284 sq ft (68K BTU/HR).  I understand that the firing rate should match the DOE Heating Capacity rating of the system.  And though the boiler is slightly undersized and slightly underfired, it seems to be working fine and heating evenly (especially during this past Northeastern cold spell). 



Should I increase the firing rate to 110K BTU/HR (to match the system Heating Capacity Input)?  If I do, wont I be consuming more energy for the same amount of heat?  Or is it more efficient to match the firing rate?  Are there any possible drawbacks if I leave it underfired? 

Charlie from wmass

Are you a licensed gas fitter ?

Adjusting gas valves is better left to a professional. Air needs to be adjusted along with the gas pressure to assure a proper burn. Combustion needs to be tested as a dirty burn will waste your heating dollars.

djthx

Underfire or Fire at its Max?

Among other things, the GB200 IM provides instruction on how clean the burners; how to adjust the burner air shutters; how to calculate the heating input, and even how to adjust the input via the combination gas valve pressure regulator.  However, I have no problem getting a qualified technician to professionally perfom these functions.  After all, the reason I'm on this site is to assure that my system is working as efficient and as safe as it could.

 

But in general, in a gas-fired steam boiler, is it more efficient to fire the boiler at its maximum rate, or can you save $ by underfiring the system?

Mike Kusiak_2

It depends....

If you are heating comfortably and evenly with your present slightly lower firing rate, I would tend toward leaving it alone.  As long as you can heat all the radiators evenly and quickly,  you have adequate steam generating capacity.



Remember, the net steam rating of the boiler includes a pickup and piping factor which effectively oversizes the boiler by 33%. So even with your slight underfiring, you still have around 25% excess steam generating capacity over what is needed to meet the needs of the actual EDR of the system.



You actually may be gaining efficiency in this case if you are running long heating cycles controlled by the thermostat, instead of building pressure and short cycling by the pressuretrol.