Approaches to multiple heating zone control for hydronic (hot water) heating systems:

Heating zone circulator pumps versus heating zone valves: which approach is better for controlling multiple heating zones in buildings?

Page top photo: eight hot water or hydronic heating zones, each served by an individual circulator pump and circulator relay control.

This article series describes how to diagnose & fix circulator pump problems on hot water or hydronic heating systems.

Which is better: heating control using zone valves or heating control using individual circulators?

Heating circulator pumps or "zone circulators" are used to force hot water from the heating boiler through radianting devices such as hot water baseboards or radiators.

The circulator is switched on as needed or in some designs may be wired to run continuously.

Here we discuss the two principal or alternative methods of multiple heating zone control:

1. One circulator pump, multiple zone valves & thermostats:
   
   Individual heating zone controls operated by thermostats that in turn operate multiple zone valves, typically all serviced by a single circulator pump
2. Multiple circulator pumps, switching relays & thermostats: (no zone valves)
   
   Individual heating zone controls operated by thermostsats that in turn operate multiple switching relays that each turn on or off individual circulator pumps, one pump for each zone.

Each approach has its advantages and dis-advantages.

I remain unconvinced that either approach is always the "only" right answer to the heating needs of a building

Our photo above illustrates the use of six individual zone control valves to manage six heating zones in a building.

Arguing whether multiple circulator pumps (photo below) or multiple zone valves is a better approach to heating zone control is like arguing religion.

Some heating contractors prefer using individual circulator pumps, one per zone, perhaps because they recall the history of unreliable zone valves which tended to clog or jam in some models by some manufacturers.

The "zone valve" gang retort that modern heating zone valves are as reliable or more reliable than [some models of] heating circulator pumps and that a zone valve costs a lot less.

On occasion we may find a third and in my opinion uncommon or hybrid case:

3. Split one or more multi-circulator zones by adding zone valves:
   
   Multiple circulator pumps and heating zones with one or more of those individual circulator pump zones "split" by using one or more zone valves.
   
   We may see this in a larger building in which more complex heating zone piping allows one of multiple circulator-opeated zones to be split into "sub zones" by adding zone valves.

Adding zone control to an existing heating system to support a building addition or to split off a heating sub-zone may be less costly by adding a zone valve than by adding a circulator pump.

Article Contents

• WHY MULTIPLE CIRCULATORS vs WHY MULTIPLE ZONE VALVES?
• AVOID INADVERTENT HOT WATER CIRCULATION in MULTIPLE CIRCULATOR SYSTEMS
• PRIORITY HEATING ZONE DESIGNS - to assure the domestic hot water supply

...

Which is Better: Multiple Zone Valves or Multiple Circulators?

The fans of heating zone valves argue that the valves are easier to install, less expensive, and require less maintenance than individual circulator pumps. You'll read below that not everyone agrees with this view.

Those less enchanted by zone valves argue that zone valves jam, stick, don't work reliably and are thus annoying. In my experience, older zone valves that I encountered in the 1970's and 1980's were often a budget model that did not perform well and were not long lasting.

But modern zone valves have in my experienced proven reliable and easy to repair.

The disenchanted also point to pumping capacity or flow rates possible with multiple circulators or variable speed circulators, and the use of circulators to operate the separate heating "zone" used

with INDIRECT FIRED WATER HEATERS.

Even when multiple circulators are in use to control heating zones in a building it may be easier to use a zone control valve if you decide to split a heating zone into two separate loops or control areas.

Details about how zone valves are installed, wired, and when needed diagnosed and repaired or replaced are given in a separate article found

at ZONE VALVES, HEATING

Reader Reports Experience with Multiple Circulators vs. Multiple Zone Valves for heating zone control

I have tried both multi pumps and motorised valves and I would like to make a few points.

Firstly, the cost of modern 60-30 or 50-30 pumps are not that much more costly than the more popular motorised valves.

When you consider the failure rate of the seemingly most popular Honeywell and their copies (normally cheaper)motorised valves the multi-pump approach is probably cheaper.

This is because of the Honeywell type design which depends on a synchronous motor running to hold the valve open and eventually the synchronous motor fails.

They are not teribly expensive but a hastle to change and if you can't do it yourself it costs a plumber/heating man.

There are better designs such as the Satchwell but are still very expensive. I use Grundfos pumps and in particular the Alpha 2 model.

It is surpurb.

My system uses 5 Alpha 2's 60-30 pumps where I have removed all the motorized valves. I have bought some on mine on Ebay which are new and work fine.

[Image at left, Grundfos alpha series variable speed circulator pump - Click to enlarge]

Another point, many heating engineers are full of s--t in saying you have to use a larger pump on large systems. I have talked to Grunfos technical people and as long as the pump is able to meet the water volume load the smaller pumps are fine.

I use the Alpha 2 rather than the Alpha 2L pump becaause of the display showing the Load being taken in Watts.

My circuits are running at between 9 and 12 watts which over a period of time represents considerable savings in electricity over the lower cost and more older 35 watt cheaper traditional model.

A couple more points to answer some of the comments made and questions.

No, you do not have to use a relay as most if not all 230 volt thermostats can cope with the small current requirements including startup currents of most modern pums like the Alpha 2.

Anonymous is wondering about water backing up into the other zones.

I wondered also and installed at the end of each loop a non-return valve.

Very simple device and very cheap from BES in the U.K. Hope this helps somebody! (Aug 17, 2012) Barney

...

How do we control hot water flow when using multiple circulator pumps?

How do we make sure hot water only enters the zone calling for heat?

Our reader asked:

When using multiple circulator pumps for zoning, what stops the water from enterning the other zones? (July 3, 2012) Anonymous

Reply: the flow control valve vs zone valves

Anon:

In a multi-circulator hot water heating system,

the flow-control valve, a check valve usually found at the boiler hot water riser pipe(s), prevents water from circulating through zone piping until the circulator for that zone begins to spin - causing a more significant pressure difference across the zone.

That check valve also prevents hot water from circulating into a zone by natural convection when the thermostat is not calling for heat.

See details of heating zone control using multiple circulators at

• CIRCULATOR PUMP MANUALS
• MULTIPLE CIRCULATORS HOW TO HOOK UP

In a multi-zone valve hot water heating system,

each room thermostat causes each individual zone valve to open in response to a call for heat.

When the zone valve is fully opened, and "end switch" in that device turns on the common circulator (which may already be running if other zones were already calling for heat).

When the call for heat ends the zone valve closes (there are several designs that make this happen), ending hot water flow through that heating zone and stopping that zone valve's request for the circulator pump to run.

See details about controlling multiple heating zones by zone valves at

• ZONE VALVES, HEATING - home
• ZONE VALVE MANUALS & WIRING INDEX

While zone valve type heating systems may also include flow control or "flo-control" check valves, it is the "closed" zone valve that assures that heat to that zone is turned off.

See CHECK VALVES, HEATING SYSTEM for details about flow control valves.

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Using Zone Valves to Control Priority Hot Water Heating Zones

Above: notice my yellow arrow pointing to the top valve ahead of the green Taco circulator and thats partly closed?

The service tech closed the valve part way to prevent one zone from becoming too hot when multiple zones are all calling for heat at the same time.

That gives a bit less flow in GPM of hot water through that zone, causing it to heat up more slowly.

Why might we do this?

Usually the total lengths of various hot water heating zone pipe loops are not identical in buildings, and it may also be the case that heat loss rates also vary among different building areas. So when multiple thermostats are all screaming "I'm cold, gimme heat" we don't want the people in the longest coldest zone to freeze to death.

Often these flow balancing valves are small and hard to spot, as we illustrate

at HOT WATER HEAT FLOW BALANCING VALVES

Another approach to balancing the heat delivery in hot water heating zones in a building is to change the circulator pump speed, as we explain in more detail

at CIRCULATORS VARIABLE SPEED 

A different approach when we want to be sure one zone is never short on heat is to use a priority heating zone set-up.

How & Why to Set up a Priority Heating Zone

What the heck is a Priority Heating Zone System?

In some buildings we may want to give priority of use of the heating boiler to a particular zone, such as when one such "zone" is used to heat the water in an indirect-fired hot water tank used to provide hot water for washing and bathing.

That's to say, we'll give heat priority to the fellow in the shower rather than the kids in the playroom.

Note: this is NOT the same as our partly-closed circulator zone flow balancing valve that we illustrated above.

That case allows heat to flow to all zones at once but reduces the flow rate through zones where a manual valve is partly closed.

In contrast, a priority zone as we explain here will turn OFF other heating zones until a call for heat from the priority zone is satisfied.

Below, using the TACO SR503-4 four zone switching relay we illustrate a Multi-Circulator Heating Zone Wiring Diagram that provides the ability to make zone 3 a priority zone.

Excerpting from the instruction manual for this control:

When any thermostat calls for heat, the appropriate circulator is energized and the isolated end switch (X and X) will start the boiler.

Priority Operation:

When the priority dip switch is set to ON and the priority zone is actuated, all other zones will stop operation until priority zone is satisfied.

When not switched to priority, all zones will operate independently.

Notice that a simple ON-OFF switch at the upper right in the schematic allows the user to specify making Zone 3 a priority zone.

This heating zone controller is more sophisticated than you might first think. More details are in the manual I'll cite below, but notice this excerpt that makes sure that a domestic hot water demand doesn't cause freeze damage elsewhere in the building.

Priority Protection Operation:

When the dip switch is set to ON, and if the priority zone calls continuously for more than one hour, power is returned to all the other zones, allowing each zone to function independently.

Once the priority zone is satisfied, the control's auto-reset is activated and the priority zone is again allowed to have priority for up to one hour starting from when it calls next.

The illustration above is excerpted from the instruction manual below where you'll find more-detailed instructions and wiring diagrams.

• TACO SR503-4 SWITCHING RELAY INSTALLATION INSTRUCTIONS [PDF] (2010) and wiring diagrams
  
  

Also see INDIRECT FIRED WATER HEATERS 

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

My plumber doesn't know how to wire the new circulator to the boiler controls

Hi,
I’m adding a new zone for a finished basement. I have a hot water heating system that presently has 4 zones: 1st floor,2nd floor and 2 radiant heat zones.

The plumber has installed the new circulator and the thermostat is in place.

Neither the plumber or electrician seem to know how to wire it all to the boiler. I’m a retired building engineer and would like to take it on. Could you offer assistance if I send you photos? On 2021-02-03 by Richard A Leto

Reply by (mod) -

Richard:

Most likely your installer simply needs to add another circulator relay that is switched by the thermostat and that is in turn wired out also to the boiler aquastat. It'd duplicate wiring already in place. Perhaps there's something we are missing here.

After decades of field investigation and forensic lab work, with exception of a few pro-bono or research assignments, I have retired from field work and also from forensic laboratory analysis work to concentrate full time on pure research and writing for InspectApedia.com.

I must send my regrets that our workload as well as the urgency of your situation preclude telephone, in-person, and any lengthy email consulting, whether pro-bono or paid, concerning the question(s) that you have raised.

It's also the case that far more reliable, safer guidance will come from having an on-site expert discuss your concerns, take a thorough case and building history, inspect the building exterior, interior, mechanical systems thoroughly if that's required, perhaps provide a bit of ancillary testing (never rely on tests alone), provide findings in writing, and answer your follow-up questions.

For environment and health related worries it's usually best to start with guidance from your own doctor.
In five decades of building, environmental, and forensic work it has been my experience that at every case in which I was able to actually visit and inspect a property there were critical observations and conditions that simply were not obvious to a normal home owner, buyer, realtor. It's not that the inspector is necessarily smarter, but rather that they have different experience.

E-text, reports, photos, phone calls are never a substitute for an on-site expert.

CONSULTANTS & EXPERTS DIRECTORIES - at https://inspectapedia.com/Expert-Consultants-Directory.php may be of some help to you.
InspectAPedia.com provides building and environmental diagnostic and repair information. Many basic questions you may have can find a better-organized and more-complete written answer at our website than we can provide with a new off-the-cuff reply.

Try the on-page search-box found at the top or bottom of any of our website pages.

One of "zone valve" legs isn't running water or getting hot. It's not an airbound zone issue.

I have a 4 legs coming off my boiler, each with a separate circulating pump.
3 of them control a single zone.

The 4th leg splits and has a pair of Taco zone valves.

Everything was fine until late spring this year, when part of one stopped heating.
Then COVID, turned off everything, and promptly forgot about all if it until this week when I needed to fire up the boiler to keep the kids warm.

One of "zone valve" legs isn't running water or getting hot. The other seems fine.

I have flushed out air and am confident it isn't an air issue, no valve issues at the other end.
If I manually pull the lever on the suspect Taco valve, water seems to flow but never shuts off and leaves the circulating pump running 24/7.

Is this actually a zone valve issue? Or a pump with too low pressure? Or wiring to the zone valve?
Thanks for any ideas - On 2020-10-31 by Mark

Reply by (mod) -

If the zone valve is open and the circulator is working water should flow through the zone;

IF it does not, beyond being air-bound (that can be subtle to find all air blockages), the circulator impeller could be damaged so even if the circ motor runs it may not be pushing water,

OR

The zone valve lever may make us think the valve is open but it could be actually shut in the valve itself (uncommon)

If problem were one of low pressure in the hydronic system you ought to see that on the pressure gauge; for a residential system at typical house height, the COLD pressure in the system is 12 psi and it
goes up to under 30 psi when hot.

You can check zone valve wiring by eliminating the thermostat from the equation - remove those wires and jump those terminals at the zone valve and watch to see if it actuates the motor and opens the valve.

When the valve is fully open the end switch on the valve closes between the valve's other two wires that turn on the circulator.

If the zone valve isn't opening when it should the valve itself may be jammed or the control head motor could be bad.

by Mark

@ - by (mod) -

Daniel Friedman, thanks much for your reply. When I went to jump the terminals, I realized I could quickly check both the suspect lever and the power head at the same time by just swapping power heads.

Sure enough, the end problem followed the head, so the lever is good and theromstat is functioning properly.

I'm starting with replacing the head. If that doesn't do it, I'll swap in a temporary circulator to check it, too. Thanks again.

Why do I get heating water flowing through zones that are OFF ?

I installed a three pump controlled system with check valves in pumps

When one zone activates I get flow through all three but more flow on the zone with pump that is suppose to be heating.

What can I do to isolate the three zones so no bleed over to other zones accuring? On 2019-11-02 by Alan

Reply by (mod) -

Alan

Start by checking the position of the control knob atop the check valves; those valves, detailed at

CHECK VALVES, HEATING SYSTEM

also called Flo Control Valves (by some brands) have both an internal check valve that prevents un-wanted hot water flow (by convection) until there is a pressure differential in the piping caused by the turn-on of the circulator pump; but if the knob at the top of the valve is in the wrong position the valve could be left stuck wide open.

Also post a photo of your boiler showing the circulators and check valves (one photo per comment) and I may be able to comment further.

Daniel Friedman

 

How do I Solve the problem that one circulator for four zones isn't heating my house correctly?

I have four heating zones, one circulator and four zone valves.

First question: Say each zone is 3 gpm. If the pump is sized for times when all four zones are calling for heat - say 12 gpm - won't that cause a problem, like noisy pipes, when only one or two zones are calling for heat? Second question:

Three of the zones are roughly the same head, but one of the zones is much longer and has at least twice the head of the other three. Won't this zone suffer when it calls for heat at the same time as the other zones?

I should add that the below was recently installed (along with a new furnace) by an HVAC company.

Previously each of my four zones had it's own circulator. On cold nights with the new setup the heat didn't keep up and the house got progressively colder, which it did not do previously.

The HVAC company says it's not the furnace because the new one has more BTU.

They are coming to replace the circulator with a more powerful one, but I am trying to understand how the one circulator can properly serve the four zones. Thanks On 2018-01-24 by Andy

Reply by (mod) -

Andy

Typically a circulator is indeed sized to handle the case of all heating zones calling for heat at the same time.

Once you've got hot water from the boiler circulating through a zone, the main difference in time to warm that zone will be the zone size and the zone area's rate of heat loss. Upping boiler temperature, increasing water flow rate, and other tricks can improve the heat delivery rate somewhat.

Other choices are available but are more trouble:

1. install baseboards rated for a higher BTUh output per linear foot

2. install larger diameter piping if your plumber, like our very disappointing one in Pougheepsie, saved a dime on the installation by using 1/2" rather than the usual 3/4" diameter heating supply piping.

3. install a variable speed or higher speed circulator

4. Find and fix points of heat loss in the cold zone, starting with drafts

Keep in mind that the zones will not be equal in size, heat loss, or other parameters - just as your case describes.

However since each zone is individually regulated by a thermostat and in your case zone valve, that means in essence that the colder zone should simply call for heat longer until satisfied.

You can play with zone balancing by closing the outlet louvers on the shorter-zone baseboards to handle the case you describe.
Also check that the long zone is actually really finned copper tubing baseboards, not just naked pipe (that has a much lower heat output rate) and check that air flow through the baseboards is not blocked in the long zone.

Just looking at the boiler's BTUh capacity is not enough. Your long zone could be partly air-bound, or there could be some other obstruction in heat outlet.

Adding a "more powerful" circulator will run water faster through all of the zones, thus somewhat increasing the delivery rate of btus to each area.

How do I control one room that's too warm when they're all on the same hot water heating zone?

Just added three hydronic radiators to the basement.

I find my basement too cold and main floor is warm.

Problem is I only have one thermostat on the main floor to control all heating. What can i do to solve this problem? On 2017-05-17 by Jae

by (mod) -

Jae,

I think you want a heating system installer or technician to take a look at the piping of your existing hot water heating system.

Typically we can split off a sub loop of an existing zone and install a separate thermostat for the loop.

See details at ZONE VALVES, HEATING

When adding zone valves and sub-zones on a hot water heat system where do we hook up the zone control?

If i decide to add a zone valve to my boiler do i have to hook it up to the relay on the boiler? (July 16, 2012) kenny

Reply:

In this installation a thermostat operates the zone valve on a call for heat, causing the zone valve to open to allow hot water to flow thorugh that zone piping loop. Then the zone valve's end-switch that closes to turn on the circulator relay.

Kenny - as you'll see in the wiring instructions for your zone valve, the thermostat causes a low voltage motor in the zone valve to OPEN the valve so that hot water can flow into the zone. When the valve is fully open, an "end switch" in turn talks to the circulator relay to tell it to start the boiler's circulator pump.

...

Continue reading at MULTIPLE CIRCULATORS HOW TO HOOK UP or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CHECK VALVES, HEATING SYSTEM - flow control valves.
• CIRCULATOR PUMPS & RELAYS - home
• CIRCULATOR PUMP RELAYS & OTHER CONTROLS  - to control hot water heat circulation
• CIRCULATOR PUMP MANUALS
• CIRCULATOR PUMPS vs ZONE VALVES
• CIRCULATORS VARIABLE SPEED - another way to manage heat delivery
• MANUALS & PARTS GUIDES - HVAC - home
• MULTIPLE CIRCULATORS HOW TO HOOK UP
• MULTIPLE HEATING ZONE CONTROL
• ZONE VALVES, HEATING - home
• ZONE DAMPERS - warm air heating system zone control.

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MULTIPLE HEATING ZONE CONTROL at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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