Baffles??? Flyash??? Well, I never cleaned it since Oct 09 install and initial fire up... so I am betting yes, it is probably dirty
Not sure on what the baffles are.
Now we're getting somewhere. A buildup of flyash on the plates and other boiler surfaces will certainly increase the stack temperature.
The baffles hang inside the boiler to make the flue gases travel the full length of the heat exchanger before leaving the base. Here are some pictures of the baffles used in the current DF520. There are two baffles like the one shown in picture #1, and they hang on hooks welded to the heat exchanger. There should be one baffle like shown in picture #2, it hangs on two V shaped brackets at the top rear of the firebox.