How to Identify Your Hydronic System

Ciculator pumps.

There are good reasons to understand the basics of your hydronic heating system, even if it’s just knowing how to identify what type of system you have. It helps the service technician when you can tell him what type of service call he’s responding to and he can troubleshoot more effectively. It also helps you weed out the inexperienced service technician or contractor. I’ve even seen home inspection reports that went into great detail about a home’s hot water heating system that turned out to be steam. True!

Starting with the question, Is this steam or hot water?, let’s go down to the boiler room.

A hot water heating system usually works by pumping heated water through a system of pipes, to the radiators, and back to the boiler. A dead giveaway to the hot water system is the pump. There are a few old hot water systems out there that don’t use pumps, but by-and-large, most have a pump. And frankly, if you have a hot water system that’s old enough to be “gravity” operated (without a pump), you should be thinking more about identifying its replacement.

Steam boiler with gauge glass.

A steam system would rarely have a circulating pump. There are some steam systems that use the hot water below the boiler’s water line as a heat source for a domestic hot water circuit or small heating loop, but they’re fairly uncommon.

A steam boiler should always have a gauge glass on the side of the boiler. This allows you to see the water level in the boiler. A hot water boiler doesn’t need this because the whole system is (or should be) full of water.

Now let’s say you’ve straightened out your home inspector on the fact he’s actually looking at a steam boiler. But now he’s too intimidated to ask if it’s a one-pipe or two-pipe system. You’ll want to volunteer this information. We need to get out of the boiler room and head upstairs for this.

You can usually tell a one-pipe from a two-pipe steam system simply by looking at the radiator. One-pipe will have just one pipe connected to the radiator and two-pipe will have two. It’s that simple. But it’s an important distinction. The two systems operate very differently and require a different mindset for troubleshooting.

One-pipe steam radiator.

Another distinction between the one-pipe and two-pipe steam system is that the one-pipe should have an air vent on the side opposite the steam inlet. But you need to be careful with this one — I’ve seen some underperforming two-pipe systems “fixed” by adding a vent to the radiator. It’s a bad idea, but they’re out there.

Most (not all) two-pipe systems will also have a steam trap on the radiator outlet. This is the device that can fail and cause the inexperienced service technician to put an air vent on a two-pipe radiator!

Two-pipe steam radiator.

So there you have it. Now when you call for service, you can tell your service technician exactly what type of system you have and help them better diagnose your service problem. (Or impress your home inspector.)

Heidronically yours,

Wayne