one riser or two?

DD_2

I have a Utica PEG 150C. I am going to have the
near-boiler piping redone due to a poor job by the
plumber who installed it. The piping has 2 risers as
per the manual, but the takeoffs are between the
risers rather than after the last riser. Two weeks
ago I had water coming out of my radiators.

My new plumber, who knows his stuff, is offering me
two options: complete repiping while keeping the 2
risers, or a smaller repiping that eliminates one of
the risers. The difference in price is $500. He says
that he rarely sees Uticas with 2 risers. I
understand that with a single riser the boiler runs
less efficiently, but how big would the difference be?

There are 2 takeoffs from the header. I suppose in
the worst case my gas bill doubles because the boiler
has to run twice as long to deliver steam, but I
assume the actual number is somewhat below this. Any
ball park estimate of the percentage change in my
monthly gas bill (currently about $225 for heat) would
be appreciated.