Best Of

You want either a cast iron 3 pass boiler, or a System 2000 by Energy Kinetics. Outdoor reset is useless on an oil fired system that isn't piped for it, with a buffer tank or high mass piping and emitters. Which you dont have. And oil fired boilers use an operating control that doesn't modulate, but fires to limit, whatever that limit may be.

You should have a heat loss calculation done, even though the smallest oil fired boiler is too big for most homes up to 3,000 sq. ft. if you consider a 75K BTU net. That gives you 25 BTU per sq. ft. For 95% of the heating season, that's too much. Unless you see sub zero temperatures often.

Honeywell, Hydrostat, and Beckett all have operating controls with economy settings that work well without using Outdoor Reset.

I don't recommend either of the boilers offered unless there's space or cost issues. They're both pin HX boilers. If space is the concern, Buderus offers a stackable G115 over their indirect water heater, and System 2000 offers the Frontier on a pedestal with their water heater underneath.

Those are decent but low end boilers, they are perfectly fine but not the most efficient. The more efficient boilers that are available in oil are Energy Kinetics, Viessman, and I think certain Peerless models. There may be a few more but the more efficient models have a multi pass HX design of one form or another. You might gain something like 5% to 10% over your old boiler assuming the old and new boilers are set up to not short cycle. If the old boiler was oversized or set up improperly you might gain more efficiency if you size the new boiler more closely to the loss of the house.

The modulating, condensing boilers are only available in gas so the most efficient boilers are not available in oil.

What kind of emitters do you have? Are they cast iron radiators or fin tube baseboard, or convector cabinets or radiant tubing or what?