Two homes on the same NYC block can have completely different heating systems in the basement. Knowing whether you have a steam boiler or a hot-water (hydronic) boiler helps you understand the noises it makes, the problems it has, and who should work on it.
How to tell which one you have
- Steam: radiators are usually tall cast-iron units, often with a small air vent on the side that hisses. There’s typically one pipe (one-pipe steam) or two pipes (two-pipe) into each radiator. The boiler has a sight glass showing a water level, and a pressure gauge reading in low numbers.
- Hot water (hydronic): heat usually comes from baseboard units along the wall, or from radiators that stay fully warm top to bottom. There’s a circulator pump on or near the boiler, an expansion tank, and the system runs under steady water pressure (often around 12–15 psi).
How they heat
A steam boiler boils water into steam, which rises through the pipes on its own and gives up heat as it condenses back to water and drains down. A hot-water system never boils, it heats water and a pump pushes it in a loop through the baseboard or radiators and back.
How they fail differently
- Steam problems tend to be about pressure, water level, and venting: banging pipes (water hammer), cold radiators from stuck vents, and low-water cutoffs shutting the boiler down. Steam runs on ounces of pressure, and a system set too high wastes fuel and bangs.
- Hot-water problems tend to be about circulation and pressure: a dead circulator pump, a stuck zone valve leaving one area cold, a waterlogged expansion tank, or air trapped in the loops causing gurgling and lukewarm baseboard.
Steam is a specialty. A tech who’s great with hot-water systems isn’t automatically good with steam, and vice versa. If you have steam heat, it’s worth getting someone who genuinely knows it, that’s a big part of why NYC steam systems get misdiagnosed.
Which is better?
Neither is “better” in the abstract, they’re just different, and most NYC buildings have whatever was installed decades ago. Hot-water systems are generally easier to zone and control room by room. Steam is simpler mechanically and extremely durable, which is why so much of prewar New York still runs on it. When either one reaches the end of its life, a licensed installer can walk you through your replacement options.