HVAC in Boston is a cellar full of old heat trying to serve three floors through one system. Steam radiators knock in triple-deckers from Dorchester to Charlestown. Hot-water baseboard shows up in later houses in West Roxbury and Hyde Park. Window units cool one bedroom and drip onto a porch roof. Start with what is actually down there.
One boiler for several households means a no-heat call is a building call. Air in the steam mains, a failed vent on the top-floor radiator, and a water line that is wrong can leave the third floor cold while the first floor bakes. Oil tanks in basements sit next to finished rooms that were never supposed to be bedrooms. A smell of oil or flue gas is not a filter problem. Say what you smell and which floor is cold.
Outdoor condensers for ductless heads end up in side yards that are already full of meters, bins, and a bulkhead. Salt air in East Boston, the Seaport edges, and South Boston is hard on coils. A head in a finished attic does not fix ice dams, and it does not replace a boiler that is cracked. Summer humidity in a brick row on the South End loads the air even when the temperature is moderate. Ask whether you need heat, cooling, or a system that is unsafe.
Chimneys that once served a coal boiler may be the wrong size for the appliance now tied to them. Spillage at the draft hood, soot on the front of the boiler, and a CO alarm that chirps are reasons to stop guessing. Radiator valves leak onto hardwood and look like a roof leak to the people downstairs. Know the difference when you call: a wet ceiling under a bath is plumbing, and a wet ceiling under a radiator is heat piping. Describe the location.
Have the fuel, the type of system, and the floor that fails. Say whether the building is a triple-decker, a brick row, or a freestanding house. Mention a recent shutoff, a burned smell, or a tank that is low. You do not need the model plate if you cannot reach it safely. Call the number on this page.