New high efficiency boilers are able to reach an efficiency level close to 90%, compared to 60% or less for older models. Also old steam pipes are typically wrapped with asbestos insulation. Any pipe without insulation can allow steam to condense before it reaches some radiators, thus rendering it ineffective. If you have steam pipes; be sure to install replacement insulation it will eliminate the asbestos.
Call James Vito for a free estimate for a new boiler.