I have a burnham holiday boiler no. 8-60 series 2 that recently combustion tested at 80% efficiency. I think the boiler was probably manufactured in 1960 based on the boiler no. It's 172k input and 140k btu output.
All advice is that if the boiler's over 15-20 years old it should be replaced. Why? If it's 80% efficient and has been reliable for 50 years, why drop $10k for something only marginally better? (I'm not interested in ModCon because the extra cost of servicing and shorter lifespan make them uneconomical for my limited needs).
Presumably a new one would be smaller (my heatloss calculation is 90K btu Max) and have sealed combustion, electronic ignition, and perhaps less jacket loss (though hard to tell). Does anyone have any real world experience with the savings expected with a newer smaller boiler?
Right now we're using about 1150 CCF of gas per year or about $2300. I estimate that about 250 CCF of the 1150 are for DHW.