Humming/groaning sound when boiler kicks on

[BadgerBoilerMN]

This bears repeating; "Uninsulated exposed poured concrete foundation is good for about R1. Uninsulated band joists no more than R2. The air leak at the band-joist/foundation sill in most homes is bigger than all of the window & door leakage combined."

There is no such thing as DIY condensing boilers...I know, I know; but come back and tell us how it is going in 5 years or so.