If the existing steam radiators and distribution piping are sound, a well-tuned one-pipe steam system with a new high-efficiency boiler is competitive with modern forced-hot-water systems on efficiency and significantly less expensive to install — because you keep all the existing radiators. The upgrade cost is mostly the boiler itself. Converting to forced hot water means replacing every radiator with baseboard or panel radiators, which is a much larger project. We'd recommend a steam system assessment first; many Bay Ridge buildings are better served by a boiler upgrade than a full conversion.
Low pressure specifically on upper floors in a pre-war Bay Ridge building is almost always galvanized supply risers that have narrowed internally. The fix is repiping those risers with copper or PEX. In a two-family, that typically means replacing the main riser from the basement to the top floor and the branch connections on each level — a job we can usually complete in one to two days depending on access.
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