Replacing Burnham 140,000 BTU Gas/Hotwater system

[cpeters]

I'm thinking about replacing my Burnham 65W circa 1977 boiler with a newer
model. The boiler had a tankless heater which is deactivated and was originally oil fired later converted to gas.
I can't believe that the effeciency is of 60% because of the oil chamber and
the flue size. I would like some of good quality like a Burnham or Weil Mclain with about 85% effiency.
Can I repipe the system using M copper instead of the iron with 50/50 solder or do I need 95/5.
My local dealer recommended a Crown Boiler?Cabo2. But $2400 seem a little pricey.
Can I get rid of the flow controls? I have 2 circulator pumps.
Thanks for your help.

[hj]

An oil, or coal, conversion to gas is always less efficient because of the larger flue passages. We used to install baffle material to force the gases to slow down and stay in closer contact to the heating surfaces. Only an on site inspection could tell which, if any, devices are not needed.

[jadnashua]

There is something to be said about a cast iron boiler with straightforward commonly available controls. There is also a market for more sophisitcated boilers that can achieve higher efficiencies. Some of the newer boilers can exceed 94%. Weil-Mccain makes their Ultra line that is close to that. One neat thing about this type is that it has a modulating burner - mild day, you can run the burner at a low setting (which actually increases the efficiency even more) and decrease the on/off cycles which wear thing too.

The tradeoff is more expensive and more complicated vs simpler and less efficient.

Look at Viessmann, too. They are German(?) but have a factory in Rhode Island.