Mixed hydronic and radiant, same boiler

RicD

The hydronic heating boiler I'm working on was originally configured for 4 zones, although only 2 were used. I have added some radiant floor heating zones that will use the other 2 legs. My issue is that the 4 Taco 007 circulators are all on a manifold on the return side with no room to plumb around them. The best practice for the mixing valves needed for the radiant loops is to put the circulator on the outlet side of the mixing valve. Since the circulators are already plumbed in, I'd rather not move them. My question is, can I use a monoflo tee on the return line to feed the cold side of the mixing valve and leave the circulator in its current return/pull location?

Jamie Hall

no.

To make a mixing valve work at all, you have to pump out of the outlet (zone circulator)

GroundUp

You could use a mechanical mixing valve or injection rather than a thermostatic mixing valve, but otherwise no. Depending on the boiler, you may also need to add some sort of protection from the cooler radiant return temps if they're running without your high temp emitters.

Also, "hydronic" encapsulates all types of water heating and cooling- including radiant.

RicD

Technically, it is on the outlet side. they are pull pumps on the return side. Here's a rough sketch.

hot_rod

The pressure drop of the radiant circuit will be higher than the pressure drop across the 3 port valve. The path of least resistance will be across the valve not thru the circuit.
So you are not really pulling thru the valve from the H&C ports.

Here are 3 options that work well for adding a low temperature zone.

EdTheHeaterMan

You will need to move the pump for that low temperature zone. No Ands, Ifs or Buts if you are going the thermostatic mixing valve route. But that is not the end of the world. Select a convienent location for the mixing valve and place the pump on the outler side of the mixing valve. then just use a circulator flange to connect to the existing circulator flange with a gasket and 2 bolts. That will end up being an impromptu union of sorts.

Here is my impression of what you are dealing with. And the way to deal with it

hot_rod

You can pump through an un-powered circ also, leave the one in, remove the internal check if it has one, add another circ after the mix.

The jumper Ed shows can be easily made with two sweat flanges and a piece of copper tube.

EBEBRATT-Ed

Also, the sketch the OP posted. with the mixing valve.

I always thought a "mixing Valve has two inlets and one outlet and a diverting valve has 1 inlet and two outlets.

RicD

So, I guess it's inevitable I have to move the circulator. Thanks for the comments. Much appreciated.