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Jul 19, 2023

Dan Holohan: Circulators or zone valves

nimis69 / E+ via Getty Images Back in my rep days, half a lifetime ago, I sold

nimis69 / E+ via Getty Images

Back in my rep days, half a lifetime ago, I sold Bell & Gossett circulators. We didn't have a viable zone valve available at the time, and when the factory finally showed up with one, it ran on a wax-filled heat motor that was about as slow as I am now at 73 years old.

It seemed like Honeywell had most of the NYC/Metro market sewed up for zone valves back then. Their unit opened with a motor that pulled a ball away from a seat. They claimed that this was a great way to go because the ball rotated in the flow of water and always changed the way its rubber surface met the valve's seat. That had a lot of appeal to the trade because it made sense. The zone valve should last longer if it's taking advantage of the entire surface of the rubber ball.

The problem, though, was that the valve closed when the thermostat cut power to it and two springs had to drag that rubber ball toward closure, working against the onrushing water. The circulators we were using at the time were all single-speed, and when the water-lubricated circulators showed up in the 1970s with their steep performance curves the Honeywell valve tended to slam shut because the velocity of the water moving between the ball and the seat was way too much. When the valve finally shut, there was a water hammer that could wake you from a deep sleep. I know this from personal experience.

B&G's Series 100 circulator fared better with the Honeywell zone valve because it operated at 1,750 rpm and had a much flatter pump curve, compared to the new kids on the block. The Series 100 didn't produce nearly as much head pressure as the zone valve seated itself.

However, most of the contractors liked the newer circulators because of their lower cost and water lubrication (oiling circulators is often neglected). They solved the water hammer problem by disconnecting one of those two closing springs inside the Honeywell valve, or by just moving the zone valves to the return side of the system, where the circulator pressure was lower.

But that's all history. We have much smarter circulators these days, so I was wondering whether today's contractors preferred using circulators or zone valves. I posed the question on The Wall at HeatingHelp.com, which is a place where some of the smartest hydronic-minded people meet to discuss such things. They are never shy when asked a question. Here's some of what they had to say:

"I think the availability and broad options of Delta-P circulators when it comes to size are allowing the pumped-zone bunch to rethink zone valves. Thermostatic radiator valves also seem to be gaining some popularity. They’re a great match for Delta-P circulators."

I have to agree. A circulator that can sense the difference in pressure across itself as a result of zone valves opening and closing will respond by lowering the pressure it produces at times of low flow, and that is a very good thing. Not only does it save electricity, it also solves the water-hammer problem. And TRVs do seem to love those circulators.

Another Wallie said, "I have used zone valves mostly. Honeywell was my choice. I liked the Erie Pop Top when I put my own system in, but found after 25 years there were issues with the Pop Top body leaking and the valve not closing completely. I changed to Honeywell exclusively a few years back. The heat-activated, hydraulic-piston models take too long to activate, which plays havoc on the recovery of indirect water heaters by adding another minute or two to the call for hot water from the tank thermostat until the boiler water actually is hot enough to start to heat the water in the tank. If there are more than five zones, I might split the zone valves between two circulators."

And here's an exchange I wasn't expecting: "I like to zone with circulators because low-voltage wiring doesn't hold up as well against the coat hangers."

Ahh, the real world of homeowners enters the mix. But fear not, another Wallie almost instantly added this solution: "So, run heavier wire to the zone valves. Something that can hold wet quilts."

Aren't they adorable?

Then, a Wallie said this about his own system: "I have seven zones on my radiant-floor system. I’m using one circulator and seven zone valves (with actuators) on the return side. The up-front cost of going with seven circulators, along with the electricity to run them, would have been much higher. With the original, single-speed circulator, it took quite a bit of time for me to play with the supply-side zone valves (using them as restrictors) to balance things out during random, multiple-zone calls because I have a wide variety of zone lengths. Once I switched to a differential-pressure pump, things got much smoother."

A circulator that can sense the difference in pressure across itself as a result of zone valves opening and closing will respond by lowering the pressure it produces at times of low flow, and that is a very good thing.

A West Coast Wallie commented, "I use mostly Delta-P circulators. I zone my radiant systems at the manifold with telestats, if the customer requests them. I have no issue with using zone valves since the availability of Delta-P pumps is now widespread, and I no longer need to install a pressure-differential bypass valve."

So Delta-P pumps are looking good these days.

"I do design assistance for contractors," another Wallie chimed in. "We had a whole bunch of people switch to zone pumps with Delta-P circulators during the past few years. The Electric Company was offering big bucks for each pump. The offer was so good that the circulator was actually free. I like them because the Delta-p function seems to work well and eliminates a lot of the over-pumping that many systems around here experience."

A Chicago-area Wallie likes to use an old-school method that has two circulators sharing the load. When it's not too cold, you get away with using just one of the two circulators. "I prefer to use both circulators and zone valves on larger jobs," he said. "We install two circulators in parallel with outlet flow checks that can handle the full flow needed when the two operate together, and then use zone valves to control the zones. I now have backup built in on the pumping side; and I can often use small, residential-size circulators for commercial applications because I’m parallel pumping. That usually cuts the costs of the circulators, and makes replacing one, when necessary, much easier. We use full- or nearly full outdoor reset, so the zone valves are open almost all the time. That does away with the need for a variable-output circulator."

Another Chicago Wallie said, "I’m against any kind of over-zoning, but there are lots of jobs, such as apartment buildings, that require it. I prefer using a minimum number of zones and a minimum number of supply-water temperatures. When zoning makes sense, using zone valves with a Delta-P is my first choice."

Finally, a Western Wallie had this to say:

"When I see a wall covered with residential zone circulators I always wonder how many, if any, of those circs are running mid-curve. To use one of these on a radiant circuit requiring 1 GPM is ridiculous, but rarely do installers plot a system curve, much less lay it over a pump curve to see what's happening. I will say this, though: The new electronic circulators can eliminate most of the improper-sizing issues. Also, ECM circulators with DC motors have much more starting torque, so the problem of circulators getting stuck on start-up, which was once as common as failed zone-valve motors, is now a thing of the past. With a wide array of ECM circulators now available, one should be plenty for most any job. A Delta-P circulator with zone valves pretty much nails flow rates to exactly where they need to be.

So that's what the smart kids are thinking these days. I hope it helps you figure out what you want to have in stock for them.

Dan is the hydronics contributing editor for Supply House Times. He founded the popular www.HeatingHelp.com web site where you'll find just that - Heating Help. Post your technical challenges on The Wall bulletin board and get input from some of the best in the business. You can reach him at [email protected]. He loves hearing from you!