I can't tell much without knowing the unit costs in your location. Around here natural gas always wins in cost per btu compared to electricity and oil.

If your oil fired boiler is in good operating condition there may be no reason to remove it. You can probably without too much trouble leave it in place and intall the new gas fired boiler beside it. Probably a heat exchanger to boost your electric hot water heater would make sense too.

I would go with the 93% effecueint unit and either save the oil for future use or burn it in my diesel car or truck.

Good luck.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.