Prior posters seem to confuse combustion air with convection air heated by the
pumping of hot water throughout the house - just sayin'.....
Now, MY EXPERIENCE: I have a 4-year old Baxi Duo Combi condensing boiler. Heat
and hot water. GREAT, when it works, quiet, more than adequate for our 2500 sf
home in central New Hampshire. BUT this POS has failed more times in 4 years
than our prior conventional American Standard/Carlin cast iron boiler in 39
'nuff said ? 5 different service trechs, 3 different companies and still a POS
! looking for a sensible replacement at this time.