Details grasshopper details. I'm referring to the load side only with the 1.25" headers and zones. I don't think I mention anything about the boiler side circ.... when headers are sized right a bumblebee might be maxed out there, but they can flow that much. I doubt he will ever see a demand that requires that much and if so not for long. If his calculations come out different he's still a minor change away from still providing variable speed control. I like how this guy has planned and isolated his system for better performance and longevity..when you know darn well many skip or ignore that part. Just by that little detail he won't have the air/circulator associated problems and enjoy longer equipment life, while others will come on here and ask why am I still having problems.
And absolutely yes it doesn't matter where the circ is located when installed correctly. This means NOT installing a circ above boiler waterline, NOT without bleeding or isolation hardware and proper sizing calculations,,,,etc. you just can't slap a system together , fire it up and run , like we see so often. ( Not implying you do this in any way) Far too often all these pump problems are a direct result from poor installation and sizing. Just like the recent post and pictures of the eroding brass fittings in a few months. All they see (mezzmorized actually) is that initial cheapest price and never calculate the seasonal or 5-10 year costs. There is absolutely no reason these circs shouldn't last a minimum of 10 years in an open system. OWB's are not the only application that's not pressurized. Food, chemical,farm....
It sounds like atleast your supply side system is good, just by the fact that you are using a small circulator 007/15-58/bumblebee) for system supply. Less than a $100 pump for the non ECM version, Versus the guy who has gone thru 3 very large and expensive $350 plus circulators and still doesn't know why.
There isn't enough good guys like you Scott to ensure everything is done right. But by having a place where accurate info and methods can be shared, hopefully fewer bad situations can be avoided. Protecting the wood burning hydronic industry name and efficiency helps everyone.