Cross over heat transfer

Wfrcrownbwf · October 25

I have a cast iron boiler serving three zones of radiant floor heating loops. The boiler has a feed pump and each zone also has a circulator pump. Two loops are downstairs (main living space) and one in upstairs master bedroom.

The problem: when I run the upstairs zone to a comfortable temp, the system backs up flow into one of the downstairs zones causing severe over heating.

Each zone has a temp mix valve, but at 115°F and unchecked flow thru the non-active loop, it can get 75° in the family room... very uncomfortable.

Any thoughts on a solution?

HVACNUT · October 25

Check the Checks.

EBEBRATT-Ed · October 25

Check valves are in the pump, or you could have separate flow check valves. Pictures may help

Wfrcrownbwf · October 29

Check valves would stop reverse flow on the pump feed side, but how do you stop flow coming from return side back into the mix valve and thru the pump in the correct flow direction?

mattmia2 · October 29

flow checks stop forward flow unless the circulator for that zone is running.

Wfrcrownbwf · October 29

Wfrcrownbwf · October 29

Check valve can't stop forward flow at all only reverse flow. Forward flow from the pump is same as forward flow coming from the return and thru the mix valve and the thru the pump.

mattmia2 · October 29

a flow check valve is designed to prevent forward ghost flow in zones that are not on when a system is zoned by circulator. the pressure differential from the pump i that zone os more than the pressure differential in that zone from the pump in an adjacent zone. unless your system is piped wrong and the zones aren't reasonably isolated.

https://www.supplyhouse.com/Bell-Gossett-107037-1-NPT-Bronze-HydroTrol-Flow-Control-Valve

https://www.supplyhouse.com/Taco-0010-025RP-IFC-Replacement-Kit-for-Select-Taco-00-Series-Cartridge-Circulators

hot_rod · October 29

https://forum.heatinghelp.com/discussion/comment/1869846#Comment_1869846

Spring checks used in hydronics have a spring with a 1/2 psi "pop" opening. Weak enough for even a small circ to push open.

That is enough to prevent gravity or ghost flow induced by the buoyancy difference between hot and cold fluid. Which is the concept the the old gravity systems operated under.

Screenshot 2025-10-28 at 10.09.29 PM.png

Older style cast iron flo checks had a tapered weight inside that acted as the spring does,

Screenshot 2025-10-28 at 10.11.00 PM.png

Screenshot 2025-10-28 at 10.12.16 PM.png

Cross over heat transfer

Comments

Categories