Boiler Efficiency

I have a boiler which for a certain period of the year has a spesific boiler efficiency, let's call it A. For another period of the year the boiler isn't used that much, and so it now has a different boiler efficiency B for this period. How do I find the overall efficiency for the whole year?

Hope someone can help me...
 Admin Thermodynamic efficiency is pretty much independent of time, unless it degrades due to changes in the system which are time dependent, e.g. build up of deposits. If one has two time periods T1 and T2, and two rates A and B during those periods, then a simple average is (A*T1 + B*T2)/(T1+T2), otherwise one has to integrate A(t), B(t) over the corresponding times and use the appropriate averaging technique. Now as for efficiency, are you sure the problem is not calling for 'availability'. Some plants can be operable, but are not needed, and therefore will have a low capacity factor. Availablity is the time that a plant can operate, and capacity is based on the actual time of operation. A plant down for repairs has no availability.

 Quote by Astronuc If one has two time periods T1 and T2, and two rates A and B during those periods, then a simple average is (A*T1 + B*T2)/(T1+T2), otherwise one has to integrate A(t), B(t) over the corresponding times and use the appropriate averaging technique.
I think he is talking about part load and standby type efficiencies. Using the correct values for these efficiencies and using Astronu's average calculation should give a pretty good overall efficiency estimation.