"Only" about 2 feet of exposed stone foundation is a real air leak even if the mortar looks pretty tight, and even the below grade portion will leak air (and radon, water vapor, other soil gases.) A pressurized blower door test would prove it, but consider it a given. An inch (or even two, depending on your climate zone) of closed cell spray polyurethane from the slab all the way up & over the foundation sill and band joist would be in order, with unfaced batt or blown-fiber insulated nonstructural 2x4 studwall tight to the spray foam would bring it up to current code-min. An inch of rigid EPS or XPS (but not polyisocyanurate) under the bottom plate as a capillary & thermal break is usually a good idea for uninsulated slabs.)

Burning 1.10 gph of 138,000 BTU/gallon oil at 85% efficiency is a heat rate of 0.85 x 138,000 x 1.1g/hr= 129,000 BTU/hr. With 390' of radiator that works out to (129,000/ 390'= ) ~330 BTU/hr per square foot of rad. If you look at the nomo graph on p2 of the

__radiator sizing guide__ you'll see that it doesn't even come close to balancing. Even if you cranked the boiler temp to the max you'd have an average water temp of 200 or so, and getting only 200 BTU/hr per square foot out of the radiators. That means it's guaranteed to be cycling on/off during a continuous call for heat, but the thermal mass of the system is probably keeping the burn times above 5 minutes, so it's not losing a ridiculous amount of efficiency to cycling. At the water temps you're running (report back what that temperature is) turn up the thermostat several degrees and actually measure how long are the burns, and how many burns per hour. From that we can estimate the amount of cycling you'd have once you break it up into zones.

1000 gallons/year is a net117.3 million BTU (MMBTU) per year, in a climate of what, 7000 heating degree-days(?), or 16,757 BTU/HDD, which (/24=) ~700 BTU per degree-hour. Assuming a heating/cooling balance point of 65F and a 99% outside design temp of -5F (assuming central PA) that's 70 heating degrees, and an implied heat load of 70F x 700 BTU/F]= 49,000 BTU/hr.

Your radiation is limiting you to about 170 BTU/ft^2 x 390' = 66,300 BTU/hr which 1.35x your approximate heat load, which is fine.

But the boiler is delivering 129,000 BTU/hr (twice what the rads can emit) which is

__ridiculous__. If the boiler can be safely down-fired to 0.8 or lower it will run more efficiently.