If you’ve just moved into a Boston condo or brownstone, there’s a good chance you’re staring at a large metal fixture against your wall wondering what it does and how to use it. Radiators are the primary heating system in thousands of Boston’s older buildings, and while they might look intimidating, they’re actually quite simple once you understand how they work. Here’s everything you need to know.
What Is a Radiator?
A radiator is a heat distribution device connected to a central boiler system, most commonly found in Boston’s older multifamily buildings, brownstones, and condos. Rather than blowing warm air through vents like a forced-air system, radiators use steam or hot water to generate and distribute heat throughout a unit. If you’re living in a pre-war building or a classic Boston triple-decker, you almost certainly have them.
How Does the System Work?
In a steam radiator system, a boiler, typically located in the building’s basement, heats water until it becomes steam. That steam rises naturally through pipes into the radiators in each unit, warming the metal and radiating heat into the room. As the steam cools, it converts back into water and flows back down to the boiler to be reheated and circulated again.
The system is controlled by thermostats located in common areas or outside the building, not inside individual units. A computer monitors outdoor temperatures and triggers heat cycles automatically, which means you don’t control when the heat turns on the way you would with a traditional thermostat.
Key Parts of Your Radiator
There are a few components worth knowing:
Steam Valve: Located at the base of the radiator, this valve must remain fully open at all times. It is not a temperature control. Partially closing it causes water to collect inside, leading to banging noises and potential leaks. If you’re too warm, opening a window is the right solution, not touching this valve.
Steam Trap: Sits on one end of the radiator and prevents steam from escaping through the return lines. It opens once steam condenses back into water, allowing it to drain back to the boiler.
Air Vent: Allows air to escape as steam enters the radiator. Some are adjustable, some are not. If yours is painted over or clogged with dirt, it may affect performance.
Common Radiator Questions
Why is my radiator making a banging noise? This happens when steam hits standing water inside the radiator. First, make sure your steam valve is fully open. If the noise continues, the radiator may not be properly pitched toward the valve — contact your building management for help.
Why isn’t my radiator hot even though it’s warm in my unit? In many Boston buildings, heat rises naturally, so upper floors may warm up without radiators running at full capacity. The system is typically designed to maintain 68 degrees during the day and 64 degrees at night, which meets City of Boston requirements.
Can I control the heat myself? Not directly. Since thermostats are in common areas, your best tools for temperature control are opening windows when it gets too warm and keeping them fully closed when you need heat.
One Important Note for Homeowners
If you own your unit, you’re responsible for the condition of your radiators and any damage they cause to neighboring units. Have a plumber inspect your radiators, valves, and connections every couple of years and check regularly for leaks around the steam valve during heating season. Catching a small drip early is far less costly than water damage to the unit below.
Thinking about buying in Boston and have questions about what to look for in older buildings? The 617 Living team knows this market inside and out.
