Heating Help

How do we avoid flue gas condensation in high system volume/content situation?

I have a new 250K Weil Mclain CGa in this ancient gravity conversion house, with three inch mains and the lot. Many big radiators. The previous was a 270k input Janitrol. Scary gas works, w/non-safety pilot.  
Heat loss proves sizing is correct, and the system comes up with time.  However, I am nervous about flue gas condensation in the boiler due to prolonged cold return water.   
I have a bypass between the supply and return, though its only one inch.  Should bypass' be as large as the header/manifold size?
I had originally considered piping this thing with primary/secondary like a mod/con, but changed my mind when I weighed cost/time parameters. I kind of wish I had now.  W/M manual has an option for p/s piping arrangement, but strangely they also show a bypass below the closely spaced tees.  That threw me off. 
I now have a 0010 pushing the load, but I think I'll slow it down w/ a 007.
Anyone every install p/s piping on a standard, high mass setup? Would this help with avoiding flue gas condensation, since its more like injection?
I do see evidence of a small amount of moisture being produced, and the boiler has only been installed for a month.

Check the Thread on the Main Wall

About thermostatic bypass valves.

http://www.heatinghelp.com/forum-thread/133249/Bypass-with-thermostatic-valve

the culprit -

is most likely low returning water temperatures; regardless of gas (NG or LPG) condensation is accelerated once return temps fall below 150 deg F. A bypass would work (adjusted manually) and can be set and left alone but probably not the best. I like the idea of PS; a hot loop injecting into an outdoor reset controlled secondary loop. It adds a pump but then you can take advantage of the mixing capabilities of the control you choose and maybe save a buck or two on fuel. tekmar is your best bet and the one I am most familiar with but there are others as well.

256

I think you're talking about the Tekmar 256. A friend turned me on to it, and I've been offering it to customers since I installed it  on my own boiler. Works great, but you need a second relay to run the pump if its a zone valve, single pump setup. Also gets tricky when you throw a prioritized indirect DHW in there. You then need a single master relay, and a slave that runs the heat zones. 

Really wish I just did the P/S on that big boiler. I have a feeling I'll be back to make it right.