Best Of

Not that you asked but according to many people on this site and at least a few low pressure steam boiler manufacturers, all three boilers should not have lasted with the near boiler piping. We see boilers piped in similar fashion often and they often last a long time despite the welded piping. The best example may be the Weil McLain 78 with the steel welded risers welded directly to the header. There is certainly no room for expansion, no flanges, no swing joints, etc. Despite the piping, the boiler appears to have lasted roughly twenty five years. For the record, Weil McLain made the 78 series from 1993 through 2002.

With regard to your question(s), I would not install a gas power burner in the existing 78 boiler. I think you will regret it. Due to the age of the boiler and the controls I think you are on borrowed time. Replace the boiler with a W/M 80 series with a gas power burner. Measure the standing radiation and size the new boiler accordingly. Might want to follow the installation manual for piping to prevent warranty issues. I think the fuel savings will be substantial.

The SGO boilers look to be in better shape, but I believe they could be as old as 1996. If money is real tight, install a gas line and replace the oil burners with gas power burners. When the boilers finally fail, replace them with two atmospheric boilers. You might lose a little efficiency but there are less moving parts and less noise. Oh, and don't forget to follow the installation manual or some of the "Wallies" won't sleep at night.