Steam vs. Hydronic Boilers: What's the Difference?

Steam boilers heat water to steam and push it up through pipes to radiators, where it condenses back to water and returns. They're common in older Bay Ridge homes. They run at higher pressure and need the water level, the low-water cutoff, and the air vents to all be working — when one of those is off, the heat gets uneven or the boiler short-cycles.

Hydronic (hot water) boilers heat water and circulate it through loops of pipe to radiators or baseboard. They run quieter and at lower pressure, and their main enemy is air in the lines and sediment in the loop. Bleeding the air and flushing the system keeps the heat even and the circulator happy.

The maintenance is different for each, and so are the warning signs. A steam system that's short-cycling or heating unevenly usually has a water-level or vent problem. A hydronic system with cold spots usually has air in the loop. Tell me which you have and what it's doing and I'll tell you what it needs.