Trying to get ahead of the curve here. Heating season is approaching
and my boiler is old. I doubt I will replace it until absolutely
necessary, but when it happens, I will need to decide what kind to
get. House is about 2400 sq ft and climate is fairly severe
(Chicago). Hot water heat, natural gas fired. Have separate water
heater for domestic uses. The boiler I have now is a Peerless unit
from the 1980s.

I see you can get units that are 95% efficient, with sealed combustion
chambers and stainless steel heat exchangers. All of those sound like
good ideas, but how are they in practice? Do your fuel bills drop?
Do they give trouble? Do they last? Are they worth the extra $$? --
H