Zone valve selection for hydronic system.

riclyo · 12:04AM

I recently piped in an indirect water heater to my gas fired boiler.

1” pipe leaves boiler and hits manifold for (2) 3/4” pipes with (2) 3-speed circulators (UPS15-58FC) feeding (2) separate hydronic loops.

Back end of manifold (still 1”) drops down to circulator (UPS15-42) that feeds indirect.

indirect return tee’s into 1” return approx 32” below the return of the (2) 3/4” loops.

I can draw this out if needed.

I have gauges at the following locations. Boiler, supply (before manifold), indirect return, 1 for each baseboard return and 1 for baseboards combined return temp.

Indirect fires and all is good. It doesn’t seem that radiator loops have hot boiler water getting pulled into them.

Heat turned on this morning and both circulators firing and I noticed water was getting pulled from indirect based on gauge temperatures.

So isn’t safe to assume a zone valve would solve this? I’ve looked at zone valves previously and noticed there is a CV rating I need to pay attention to?

hot_rod · 1:42AM

All the circulators should have check valves in or right dowstream. That should prevent unwanted flow. Assuming it is piped correctly.

What size boiler? The 1" copper will easily move 8 gpm. Call it an 80,000 btu load you are moving at a 20∆.

80,000 into an indirect is about twice what a typical gas fired tank receives, so recovery will be fairly quick.

So a zone valve with a 7-8 Cv presents a mere 1 psi pressure drop. Most off the shelf 3/4 and 1" ZV are 7.5 - 8 gpm.

The coil size in the indirect comes into play also. Some tanks just have a 3/4 copper finned coil, so that is a bottleneck

A pic or drawing would help. Check valves are cheaper and easier to install than zone valves.

riclyo · 9:45AM

apologies for the mess!

boiler has 112,000 btu heating capacity

hot_rod · 1:48PM

ALL 3 of those circulators need to have check valves to prevent flow from one another crossing.

You can add checks into the pump body itself. If checks were installed you could have a failed or stuck open check.

If the pumps are wired to a relay the indirect may be on priority and the heat circs will not run when the indirect calls.

Air purger, expansion tank, pumps, purge valves, isolation valves, all look to be properly placed.

At least one long sweep copper ell😉

Indirect is piped as a parallel zone, it should get full boiler output on a priority call.

Ironman · 2:15PM

All three of those circulators came with check valves in the box. Whether they were installed … that may require removing the outlet flange and visibly checking.

If you install a zone valve, you MUST remove the check valve from the circulator on that zone. Check valves and zone valves don’t go together as that would cause that portion of the system to be isolated from the expansion tank when the circulator shuts off. Bad things can happen then.

riclyo · 3:25PM

Thanks for the responses!

Yes controller is set for priority and I’m a big fan of using the long sweeps!

Would that mean the (2) 58’s are pulling from the indirects feed side due to a failed or missing check valve vs pulling from its return side?

I didn’t realize the 42 came equipped with a check as there is no “C” in the part #
I will confirm this first.

hot_rod · 4:10PM

I'm not sure what year they started offering checks for the piumps.

There is a date code on the pump. 4 digits show week and year, 2297 would be 22nd week of 97.

The volute needs to be machined for the check to slide in.

Screenshot 2026-10-08 at 10.07.46 AM.png

Zone valve selection for hydronic system.

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