Assessment and heat-loss sizing first; equipment selection second — matched to fuel, housing, and venting reality. Then the old block comes out, and the near-boiler piping goes in to modern practice: proper air elimination, correct expansion tank sizing and charge, controls that actually control. Commissioning closes the job: combustion tuned with instruments, pressures set, every zone proven. A boiler that leaves without instrumented commissioning is an assumption, not an installation.
The changeover happens in mild weather — the house sits without heat for a day or three, scheduled deliberately. The Quakertown heating guide describes the two housing eras the new unit must serve; across Pennsylvania the sequence is the same in every town.