How your steam system works
The path steam takes, from the boiler and back
Low-pressure steam heats most of the older buildings in the borough. It runs at a pound or two of pressure, a fraction of a car tire's. Here is the trip.
- 01
Step 1: The boiler
The burner heats water until it boils. The steam is held at a low pressure by a control that shuts the burner off before it climbs.
- 02
Step 2: The main
Steam travels down the main pipe in the basement, pushing air ahead of it. Main vents let that air out, so the steam can go on.
- 03
Step 3: The risers
Risers carry the steam up through the building to each floor and each radiator. They are why a cold top floor is a pipe problem more often than a boiler problem.
- 04
Step 4: The radiator
Steam fills the radiator, meets cold iron and turns back into water, which gives up its heat to the room. The vent lets the air out so the steam can come in.
- 05
Step 5: The return
The water runs back down the pipe it came up, or down a separate return on a two-pipe system, to the boiler. The pipe has to slope for this to work.
- 06
Step 6: The boiler again
The water goes back into the boiler to be heated, and a low-water cutoff shuts the burner off if the level drops too far.
Reading the symptoms
What you notice, and where we look first
| What you notice | Less often | We check first | Most often |
|---|---|---|---|
| Banging when the heat comes on | Less oftenA valve that is half open | We check firstThe pitch of the pipe | Most oftenA pipe that sags and holds water |
| One radiator stays cold | Less oftenA valve that is shut | We check firstThe vent, then the valve | Most oftenA stuck air vent |
| The top floor is cold | Less oftenA riser that holds water | We check firstMain vents and the riser | Most oftenSteam condenses before it reaches the riser's top |
| Water in the gauge glass swings | Less oftenA leak in the returns | We check firstThe water and the returns | Most oftenDirty water that foams |
| The burner shuts off early | Less oftenA control that has failed | We check firstThe pressure control | Most oftenPressure set too high or a clogged pigtail |
One pipe or two
Which kind of steam system do you have?
You can tell from a radiator. Most brownstones and older walk-ups are one-pipe. If you are not sure, send us a photo of a radiator and the boiler.
One-pipe steam
One pipe brings steam into the radiator and takes the water back out. The vent sits on the side of the radiator, and the valve is open all the way or shut.
Two-pipe steam
A pipe at each end of the radiator: steam in at one, water out at the other through a trap. The valves can be set part-way.
Want someone to read your system?
We walk the building, from the boiler to the last radiator, and tell you what we see.