When More Power Isn’t Always the Winner

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The Daytona 500 is all about speed and power and getting to the finish line first. Hydronics is basically the opposite — but you’d never know that from the way most hot water heating systems are installed these days.

Historically, North American hydronic designers and installers have specified and installed circulating pumps that pump more water and use more power than what is actually needed. It’s called “over-pumping.” And if a system underperforms, the first reaction of many technicians is to install a bigger, more powerful pump. But this almost never solves the problem.

It’s a chicken vs. egg thing. Installers either don’t have the knowledge or won’t take the time to calculate the pumping requirements for the system, and wholesalers don’t stock more than a few different pump models. I’ve heard installers justify their pump choice by the “bigger is better” mentality. And wholesalers have told me that they’d stock a wider variety of pumps but the installers aren’t asking for them. That’s a shame.

In hydronics, like stock car racing, the object is to go round and round until you cross the finish line and meet your goal. But unlike stock car racing, the winner in hydronics gets there with as little effort and speed as possible. The goal is delivering the right amount of heat from the boiler to the heat emitter (radiator, radiant floor panel or baseboard heater, for example). Pushing the water faster doesn’t make that happen any better. It just wastes energy!

Over-pumping can also create a condition known as velocity noise, which is caused by the water traveling too fast through the pipe and fittings. It can also cause erosion corrosion — a wearing away, or eroding, of the pipe wall due to the scouring action of high-velocity water flow.

But there’s hope. A new generation of circulators uses variable-speed technology and highly efficient electronically commutated (ECM) motors to vary their output to the specific needs of your system. If a zone valve closes, the pump slows down. If another opens up, the pump speeds up. Some are

Variable-speed ECM circulator

designed to operate on a pressure difference. Others operate on a temperature difference. But either type delivers just the flow necessary to heat the space, and either will consume much less electricity to accomplish the same results as compared to a bigger pump.

I’ve been using these variable-speed ECM pumps for several years now and have found them to be incredibly energy-efficient and versatile — especially for systems subject to changing flow-rate requirements. But they’re not the answer for a poorly designed system. While these pumps are capable of responding to a wider range of conditions, they still have their limitations. The application of solid design principles will determine the best application for these new-generation pumps.

You could compare great hydronic pumping to the tortoise and the hare. A bigger, faster pump will just wear out your system while a slower, steadier, variable-speed pump, like the tortoise, will win the race — every time.

Heidronically yours,

Wayne

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

It's a Numbers Game

A heat-loss calculation is where it all starts. It’s the basis for sizing any new or replacement system. It’s a roadmap to a well-designed, high-performing and comfortable heating system. And it’s not hard to do. It just takes some time and a little patience.

First, I measure each room ­— length, width and height. I also measure windows and doors and categorized them by construction type. Then I check the quantities and location of insulation. Usually I make a sketch to scale. For the average home, it takes about two hours to accomplish.

Next, I enter those measurements into a worksheet or use specialized software to produce a room-by-room and whole-house heat-loss calculation. The resulting numbers are the amount of heat lost by your house on the coldest days of the heating season.

These calculations tell me (or another heating designer) what size boiler or furnace is needed. It gives me the information I need to determine how much heating element or how many ducts are needed in each room — or how hot the water needs to be. Or what the flow rates need to be. And the pump sizes, pipe diameters, tubing spacing, panel size, and on and on and on.

Without a heat-loss calculation, it’s all guesswork. Luck. A wing and a prayer.

This is your heating system. The one you’ll be living with and fueling for the next 15, 20 — even 30 years. Ask for it. Demand it. Accept no shortcuts.

Heidronically yours,

Wayne

Get to know your steam boiler’s probe-type low-water cutoff.

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Last week I discussed how to check the mechanical low-water cutoff on your steam boiler. However, more and more new steam boilers are equipped with “probe-type” low-water cutoffs that use an entirely different mechanism to detect a low-water condition and shut down your burner before an unsafe condition occurs. (For more on that, see this post on the evolution of the low-water cutoff control.)

The typical probe-type low-water cutoff is threaded into a port on your steam boiler provided by the boiler manufacturer specifically for this purpose. It’s below the normal water level but just above the level of the bottom sight-glass port. This type of low-water cutoff operates by monitoring the electrical continuity of the boiler water. Simply put, when the probe is exposed to water, it allows the burner to operate. And when it’s exposed to air (as in a low-water condition) it does not.

McDonnell & Miller PSE-800

Some probe-type low-water cutoffs allow the burner to operate for a little bit after they sense a low-water condition — usually about 30 seconds. This is to prevent nuisance shutdowns due to temporary conditions, such as foaming or slow return of system condensate. A flashing light on the low-water cutoff control enclosure usually indicates this type of condition. If the probe senses water again within the 30-second window, the light will stop flashing and the burner continue firing without interruption.

Probe-type low-water cutoffs are either manually or automatically reset. Most residential steam boilers use automatic reset to let the boiler continue heating once the low-water condition is corrected — as when an automatic water feeder is used. A manual reset would require human intervention — a strategy that may not be in your best interest if the boiler were to shut down on low water when you’re away for a few days during the winter.

With either type, you can periodically check the device’s electronics by pressing and holding the test button while the burner is firing. A light will usually flash for a period of time and then the burner will shut down. Releasing the test button should start the burner and return the system to normal operation.

A probe-type low-water cutoff doesn’t require the same weekly maintenance as its mechanical cousin. But during the annual maintenance of your system, I’ll check your cutoff by lowering the water level to simulate an actual low-water condition. And every five years, I’ll remove the probe for cleaning and inspection. If your probe is older than 10 years, I should replace it for you.

With just a little attention, your probe-type low-water cutoff should provide years of reliable protection for your steam heating system.

Heidronically yours,

Wayne